Genchem1 Flashcards
(165 cards)
0
Q
what is an atom made up of?
A
Protons Neutrons and Electrons. The number of protons is the atomic number which it has on the periodic table.
1
Q
how many atoms would fit across the width or your hair?
A
about a million thats how small they are.
2
Q
how does electron neutron and protons masses compare?
A
neutron and proton are the same electron is about 1800 times less
3
Q
what is the number of protons + the number of neutrons?
A
The mass number
4
Q
if youre talking about a specific atom for example carbon. Can the number of protons change and still be considered carbon?
A
No they cant, the number of protons never changes. However the number of neutrons can change and the atom is still considered carbon just a different form. these are called isotopes
5
Q
how are electrons arranged around the nucleus?
A
There are energy levels in which these electrons fall in. They will always try to fill the closest orbital first. Which is closest to the nucleus
6
Q
how do you know how many electrons are in a atom?
A
The number of electrons is equal to the number of protons which is the atomic number on the periodic table
7
Q
how many electrons can the first three levels hold?
A
2 , 8, 8
8
Q
what does the group number the atom is found in on the periodic table tell you about that atoms electrons?
A
The group number will tell you how many atoms are located in the outer energy level.
9
Q
what happens to the energy level of electrons as they are further away from the nucleus in there orbitals
A
The energy goes up.
10
Q
Just a note
A
circles around the nucleus to represent energy levels mislead us. Electrons dont actually orbit the nucleus
11
Q
what hold nuclei ( protons and neutrons ) together?
A
Strong nuclear forces bind nuclei together. Electro static pulls them away
12
Q
how could you represent an atom to show how many protons it has and how many protons and neutrons it has?
A
12C
6
the C should be much bigger a lot of the times the mcat will represent the A as the mass number (protons + Neutrons) and Z as the atomic number (number of protons)
13
Q
what is the bohr model?
A
the bohr model is the representation of how the atom is set up. The nucleus is in the middle with pros and neutrs. There are then electron levels in which the electrons reside in. They dont orbit the nucleus however.
14
Q
what is an isotope? Do they all have odd mass numbers?
A
an isotope is basically just a different version of that atom. The atomic number (# of protons) will still be the same but the change in the number of neutrons is what gives an isotope. No they dont, for example carbon 14 has 7 protons and 7 neutrons. Making the mass number 14 which is even .
15
Q
what is a cation? what is an anion?
A
A cation is a positively charged atom ( less number of electrons than protons). An anion is neg charged ( more elec than pros)
16
Q
do metals form cations or anions?
A
metals from cations. non metals for anions.
17
Q
A student introduces a particle of unknown identity between two oppositely charged electrodes and notes that it accelerates toward one of the two electrodes? what could this particle not be?
A
A neutron. Cation and anion both have charge and so do pro and elc
18
Q
what happens to atomic radius as you go down a column on the p table?
A
The radius gets bigger. This is obvious because the atomic number increases as well as do the electrons making the radius bigger.
19
Q
What happens to radius as you go across the periodic table?
A
The atoms get smaller which in turn decreases the radius of the atom. However, you have to ignore the noble gases they DONT follow this rule.
20
Q
what is ionization energy?
A
The energy required to remove an electron from the neutral state of an atom or turn an atom into a cation
21
Q
What is the trend of ionization energy on the periodic table?
A
The ionization energy goes from left to right. As the you to the right the energy required to remove an electron is far more than the atoms on the left side of the table. This is because an atom is in its most stable form when the outer most shell of that atom is full. So the atoms in the first column, if they lose one they have there outer most shell full. Also as you go down the table the number of electrons increases for each atom. This means that they are further away from the nucleus so they are even more willing to give up there electron because the nucleus isn’t attracting them as much as the electrons that are closer to the nucleus
22
Q
what is electronegativity?
A
it basically the hogging of electrons. If you have a water molecule there will be more electrons around the oxygen than hydrogens.
23
Q
What would be the periodic trend for electronegativity?
A
Well think about ionization energy. The atoms that want to hold on to their electrons more because they are stable with how they are are going to be more electronegative.
24
what is metallic nature or character?
This is very similar to the ionization energy of an atom. When something has a metallic character it gives up its electrons easier. So the atoms in the bottom left that have a single electron in its outer most shell which is far ways from the nucleus because it has so many protons, will have a higher metallic character than say Fluorine that doesn't give up its electrons easy
25
what is the atomic radius?
The atomic radius is basically just how big the atom is. The atom doesnt have a perfectly spherical shape so this is hard to measure. Sometime people measure it by taking some two atoms bonding them and then diving that length of the bond by two.
26
whats the periodic trend for atomic radii
As you go from left it right the atoms get more protons and thus more electrons. The electrons however stay in the orbital and don't get further away so this cause the nucleus to pull and the electrons and decrease the size. Top to bottom however gains electrons too but these electrons aren't in the same orbital so they get further away from the nucleus making them bigger.
27
how atomic radi trends work
From lithium to fluorine, those electrons are all in the 2-level, being screened by the 1s2 electrons. The increasing number of protons in the nucleus as you go across the period pulls the electrons in more tightly. The amount of screening is constant for all of these elements.
28
what is electron affinity?
Its basically the energy release when an atom gains an electron.
29
Whats a good way to determine if something has a high electron affinity?
If the atom has a stronger attraction toward electrons. When they come in contact more energy will be released.
30
where is electrons affinity mainly happen? what groups on the periodic table?
Mainly 6 and 7. As you go down electron affinity decreases but Florine is an exception. You would think Florine is higher than Chlorine but Florine is less.
31
Metals
```
Usually have 1-3 electrons in their outer shell.
Lose their valence electrons easily.
Form oxides that are basic.
Are good reducing agents.
Have lower electronegativities.
```
32
Non metals
```
Usually have 4-8 electrons in their outer shell.
Gain or share valence electrons easily.
Form oxides that are acidic.
Are good oxidizing agents.
Have higher electronegativities.
```
33
Where are the alkali metals on the p table?
Alkali i think of basic, so like sodium potassium. This group is on the far left. don't count hydrogen though.
34
Alkaline (earth) metals p table?
the group right next to the alkali metals. This will have like magnesium ect.
35
where are the transition metals?
the middle of the periodic table
36
The lanthanides p table?
these is the first row down under. Should be inserted in as one but took it out so they could group it. look at atomic number.
37
actinides?
right below the lanthanides. look at atomic number and it will show where it should be located .
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noble gases?
far right. Helium ect
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halogens?
Florine and down
40
s d p f blocks?
s is the far left, it includes helium as well. d block is all the middle elements. p is the elements on the right. f is the lower two rows (lanthanides and actinides)
41
what is a good way to think of metals?
metals are large atoms with loosely held electrons. These electrons are held loosely because metals like to form positive ions.
42
what are some good characteristics of metals?
lustrous, ductile, malleable, and good conductors of heat and electricity .
43
how can you think of non metals?
non metals are just smaller atoms that like to hold on to their electrons.
44
do non metals form anions or cations?
anions, they hold on to there electrons which makes them more so to gain an electron
45
do metals have a higher melting point than non metals?
no
46
what kind of bond do non metals form with non metals?
covalent
47
why does size matter?
all the trends can base off of the atomic radius of an atom. Smaller atoms nuclei is closer to there valence electrons so those electrons are held more tightly to the positively charged nucleus. which causes an atom to be more electronegative, have higher ionization energy, greater electron affinity, and less metallic character than a larger atom.
48
Are larger atoms better at stabilizing charges? Why or why not?
?
| and larger atoms have d orbitals where they can "house" extra electrons
49
Families in the same column will behave similar in what ways?
both physically and chemically SiH4 and CH4 will behave similar.
50
why when atoms increase in size do the electrons in the valence shield feel less of a effective nuclear charge?
because the electrons in lower orbitals are blocking this nuclear charge. (basically pulling in on is what effective nuclear charge means)
51
Electron affinity- down and up and across what happens?
As you go down it decreases and as you go to the left it decreases.
52
Electronegativity trends?
As you go down it decreases as you go to the right it increases.
53
Ionization energy trends?
?
54
atomic radius trend?
as you go down it gets bigger, as you go to the right it gets smaller.
55
metallic character trend?
as you go down it increases. As you go to the right it decreases.
56
do electrons orbit?
no they inhabit a space know as an orbital
57
whats a good way to think about orbitals?
a region of space in which an electron or electrons live. We know that depending on the orbital in which its in it will have different amounts of energy
58
what does the 1 and s mean orbital 1s?
1 refers to the energy level that is closest to the nucleus and the s tells you about the shape of the orbital .
59
what does a p orbital look like?
it looks like two balloons tied at the nucleus
60
at any one energy level is it possible to have three p orbitals?
yes, but not at energy level 1 this one has s character.
61
d orbitals.
In addition to s and p orbitals, there are two other sets of orbitals which become available for electrons to inhabit at higher energy levels. At the third level, there is a set of five d orbitals (with complicated shapes and names) as well as the 3s and 3p orbitals (3px, 3py, 3pz). At the third level there are a total of nine orbitals altogether.
At the fourth level, as well the 4s and 4p and 4d orbitals there are an additional seven f orbitals - 16 orbitals in all. s, p, d and f orbitals are then available at all higher energy levels as well.
62
orbitals
You can think of an atom as a very bizarre house (like an inverted pyramid!) - with the nucleus living on the ground floor, and then various rooms (orbitals) on the higher floors occupied by the electrons. On the first floor there is only 1 room (the 1s orbital); on the second floor there are 4 rooms (the 2s, 2px, 2py and 2pz orbitals); on the third floor there are 9 rooms (one 3s orbital, three 3p orbitals and five 3d orbitals); and so on. But the rooms aren't very big . . . Each orbital can only hold 2 electrons.
63
Electron Configuration
For example, although we haven't yet met the electronic structure of chlorine, you could write it as 1s22s22p63s23px23py23pz1.
Notice that the 2p electrons are all lumped together whereas the 3p ones are shown in full. The logic is that the 3p electrons will be involved in bonding because they are on the outside of the atom, whereas the 2p electrons are buried deep in the atom and aren't really of any interest.
64
what are the two short cuts you can use when writing out electron configuration?
you dont have to write out 2p 2px 2py 2px unless 2 is the outer most energy level. Also you can start from Ne to shorten up the line
S 1s22s22p63s23px23py13pz1 [Ne]3s23px23py13pz1
65
electron configuration
There is strong evidence for this in the similarities in the chemistry of elements like sodium (1s22s22p63s1) and potassium (1s22s22p63s23p64s1)
66
what does the period of the row tell us about electron configuration?
This tells us what energy level it goes to 1,2,3 ect
67
what electrons are in a higher energy state Ti 1s2 2s2 2p6 3s2 3p6 3d2 4s2?
d orbital electrons are going to contain a higher energy than the 4p orbital ones. But the 4s2 are the valence so they are going to react if they do.
68
what is an energy level?
The energy level represents the energy level of the electrons in atoms. The bohr model explains this. These are quantized meaning that they look like stair steps. Electrons can be in energy level 1 or two but never in between.
69
how does an electron gain or loose its energy?
usually through a photon of light. Because electrons are quantized they can just move from energy level to energy level. They have to be struck will an amount of equal to the difference. So in other words if an electron is at the lowest state with 0 energy and it wants to move up to an energy level that requires 4ev then thats how much energy of light photon it must absorb.
70
will electrons absorb an amount of energy that isnt equal to the difference in energy between the two levels?
No, it will pass through it. The energy that strikes the photon must be equal to difference in energy between the two levels. so say 0 and the next level you need 4ev. If an electron is struck by a photon with an energy that is lower other than the difference in energy between two energy levels in that atom, the photon will pass through the atom without being absorbed. If an electron drops to a lower energy level, energy is released and the amount released is the exact same amount in the difference between the two energy levels.
71
what is the photoelectric effect?
when light is shown on a metal surface this can cause electrons to escape because it gives them energy
the kinetic energy of the electrons is linearly proportional to the frequency of the incident radiation above a threshold value of ν0 (no current is observed below ν0), and the kinetic energy is independent of the intensity of the radiation.
-the number of eimitted electrons (i.e. the electric current) is proportional to the intensity and independent of the frequency of the incident radiation above the threshold value of ν0 (no current is observed below ν0).
72
what is the energy called that is expended when an electron escapes the metal in the photo electric effect?
This is called the work function of the metal. the energy of the electron is then the energy of the photon-work function= energy of electron
73
What is the work function?
If you bomb certain metals with energy, this can cause the electrons to be ejected from there outer most shell ( the valence electrons). The amount of energy required to do so is called the work function. This only relates to metals so dont get it confused will ionization energy.
74
what happens if you add less energy than the work function? more energy than the work function?
the electrons wont be ejected, the excess energy will be transferred into kinetic energy.
75
what is the equation to see how much KE an electron may have when it get ejected from a metal?
KE = E-Φ E is the amount of energy added and KE is the KE of the ejected electron. E can also be replaced by hf to give E=hf
h=planks constant (which is alway given) and f= frequency
76
how could you calculate the energy of a photon only by knowing the velocity and wavelength?
if you know the velocity and wave length you can find the frequency because v = wavelength * frequency then you know planks which would give you the energy
77
A certain metal is know to have a work function of 500J. If a photon strikes the surface of the metal, what will be the result?
they wont be ejected because there will be 0 velocity? the work function is the amount of energy it needs to exceed in order for the electron to be ejected.
78
what is frequency?
Frequency describes the number of waves that pass a fixed place in a given amount of time.
79
What if you have two energy sources of light striking a metal will 350 J and 450 J the work function of the metal is 250 J. Which one will eject more electrons?
They will eject the same amount. Energy doesnt have to do with the amount ejected the frequency of the wave does.
80
what is radio active decay?
its when unstable atoms change their chemical composition over time. And all the action is happening in the nucleus with the protons and neutrons and there positrons and neutrons.
81
what is alpha decay?
Alpha decay the loss of one He nucleus. That is the atom loses two protons and two neutrons. He has a atomic number of 2 and mass number of 4.
82
what is beta decay?
The neutron feels like changing into a proton, so the neutron itself loses an electron which then causes it to have a positive charge and therefore a proton.
83
What is electron capture?
a type of radioactive decay in which a proton is changed into a neutron by the capture of an electron.
84
Positron emission?
A proton is changed into a neutron by the expulsion of a positron.
85
what is gamma emission?
Gamma rays are usually emitted as a byproduct of the types of decay outlined above. Gamma decay does not change the number of nucleons.
86
how should you think about what a neutron is?
a neutron is basically just a proton + electron
87
how should you think about what a proton is?
proton = neutron + a positron
88
Often the MCAT will use conservation of momentum and radioactive decay in one.
If an element of 56Fe originally at rest ejects an alpha particle with a speed of 2.0 * 10^5 m/s, what is the identity of the new element formed and what is its velocity?
well it would lose 2 neutrons and 2 protons so there would be 24 protons and 28 neutrons so the element would be Cr. Then use conservation of momentum to solve.
89
what is the half life (t1/2) or something?
this is the amount of time required for exactly one half of the mass of that substance to disappear due to radioactive decay.
90
what are the three variables they typically give you in a half life problem?
the half life (t1/2) , time elapsed (t), and the amount of the substance (g)
Solve these half life conceptually in your head 50 grams it has a 10 year half life. what will it be after 20 years? 12.5 grams
91
you have 500 g and the half life is 10 years how much will there be after 40 years?
31.25 grams
92
For half life they may give you the intial and final concentrations of a substance plus the amount of time elapsed and ask you to solve for the half life. how would yo do this?
first decide how many times the substance had to be cut in half to go from the initial to the final value (ie the number of half lives it took). Dived the total time elapsed by the number of half lives it took to get the length of each half life.
Always take notes when doing half lives so you dont make any mistakes.
93
what is the difference between anit bonding orbitals and bonding orbitals? what do each look like?
- Anit boding orbitals are higher in energy than bonding orbitals
- Bonding orbitals contain electrons that are "in phase" and are said to be attractive. Anti bonding orbitals contain electrons that are out of phase and are said to be repulsive.
for a bonding the two orbitals form the atoms come together and form as one. anti bonding they spit into a higher energy orbital and a lower energy orbital .
94
when atoms react and form bonds what are they trying to do?
they try to achieve noble gas structure, they do this through either transferring electrons to each other ( ionic bond) or by sharing electrons with each other (covalent bond).
Hydrogen atoms only need two electrons in their outer level to reach the noble gas structure of helium. Once again, the covalent bond holds the two atoms together because the pair of electrons is attracted to both nuclei.
95
what is an electrolyte?
electrolytes are substances which when dissolved break up into cations and anions.
96
Good vs poor electrolytes?
covalent compounds that dissociate 100% in water, such as strin acids and strong bases, make good electrolytes. Other covalent compounds are usually poor electrolytes.
-IONIC COMPOUNDS THAT ARE SOLUBLE IN WATER ALWAYS MAKE GOOD ELECTROLYTES.
97
what is a polar bond?
When two atoms are bonded together but one is way more electronegative than the other so it has more electron density. Like HF
98
How do you think about ionic and covalent bonds that helps?
So what would be a bond that would exhibit the most ionic character if you could choose 2 atoms off the p table?
basically the larger the difference in electronegativity over 1.7 is going to give you an ionic. A bond between .5 and 1.7 will be polar covalent and something that is non polar covalent is below .5.
it would be the least electronegative element and the most electronegative element.
99
How to tell if something has ionic character
All bonds that are not between two atoms of the same element have som ionic character. It is basically a measure of the polarity of the bond. Ionic species such as NACL have close to 100% ionic character.
100
What is condosity?
If i have a 2M KCl solution what will expect the condosity to be?
Condosity is the concentration (Molarity) of an NaCl solution that will conduct electricity exactly as well as the solution in question.
Since K is more metallic than Na, we know that it is a better conductor. Therefore, the condosity will be something greater than 2.
101
What is bond length
The distance between the nuclei of the atoms forming the bond.
102
what is bond energy? do stable compounds have high or low bond energies?
The energy stored in the bond; the energy required to break the bond.
Stable compounds have high bond energies
103
Does a high energy molecule have high bond energy?
No, a high energy molecule is unstable and requires very little energy to dissociate the bond.
104
What is bond dissociation energy
Same thing as bond energy; the amount of energy required to break the bond.
105
what is heat of combustion? And do high energy molecules or low energy molecules have a higher heat of combustion?
Amount of energy released when a molecule is combusted with oxygen. The higher the energy of the molecule (less stable) the higher the heat of combustion.
106
why do bonds form? is energy required or released when a bond is formed?
Bonds form so the atoms can become more stable. Remember they want to be like those noble gases.
Bond formation makes the participants more stable so they loose energy. It is the same as you loosing energy and relaxing on your couch. It takes energy to break bonds
107
why is the heat of combustion greatest for the most unstable molecules?
?
108
what is a coordinate covalent bond?
this a covalent bond in which both electrons shared in the bond are donated by one atom. This atom must have a lone pair. If a molecule doesnt have a lone pair of electrons it CANNOT form coordinate covalent bonds with metals or other Lewis acids.
109
describe what a mole is?
A mole is a unit of measurement. Its like a dozen. Lets say you have 1 mole of carbon this also means that you have 12.1 grams of carbon. This also means that you have 6.022*10^23 atoms of carbon
110
whats the difference between molecular and empirical formula?
The empirical formula is just the ratio
111
what does percent mass equal?
percent mass = (mass of one element/total mass of the compound) *(100%)
112
what is the percent mass of carbon in glucose? (C6H12O6)
(72/180)*100 40%
113
How do you derive a formula from percent mass?
1) change each percentage of each element into grams (15%=15g)
2) convert the grams of each element into moles by dividing by there molar mass
3) Look at the element with the lowest number of moles. Calculate approximately how many time it will divide into each of the other molar amounts for each of the other elements-this number will be the subscript for each element in the empirical formula. If the numbers aren't to the lowest possibility divide it by a common denominator.
114
Can you find the molecular formula if you have just been given percent mass of each element?
NO! An empirical formula is all you can get from percent mass alone. To get the molecular formula, you must be given the MW of the unknown compound.
115
how do you name general ionic compounds? The nomenclature of inorganic is primarily the naming of ionic compounds.
Name the cation first, then the anion. ( Calcium sulfate is CaSO4)
116
How do you name transition metals?
When written in words, compounds that include transition elements must have a Roman numeral showing the oxidation state of the metal ( iron(2)sulfate vs iron(3)sulfate)
117
naming of monoatomic ions?
These are named by replacing the last syllable with -ide (chloride, sulfide, hydride)
118
what is the formula for hydroxide?
OH -
119
Nitrate?
NO3 -
120
Nitrite?
NO2-
121
Chlorate and Chlorite and Hypochlorite, Perchlorate
ClO3 - ClO2- ClO- ClO4 -
122
Bicarbonate
HCO3-
123
carbonate
CO2^3-
124
ammonium
NH4+
125
Sulfate
SO4^2-
126
Phosphate
PO4^3-
127
Permanganate
MnO4-
128
Cyanide
CN-
129
Manganite
MnO2-
130
For acids if the ion name ends in -ate what should you replace it with?
-ic Like Nitrate would be Nitric
131
For an acid if the ion name ends in ite what should you replace it with?
-ous as in Nitrite it would be Nitrous Acid
132
For acids if the parent is a single ion rather than a polyatomic ion what should you do?
Replace the -ide ending with -ic and add Hydro at the beginning. as in Iodine this would be Hydroiodic acid.
133
How do you name binary compounds?
Name the element furthest down and to the left on the p table first. Use poly prefix as necessary. ( Nitrogen Trioxide, Sulfur Dioxide). Some have common names such as ammonia and water.
134
What is a combination reaction?
Combination- A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of: A + B ---> AB
8 Fe + S8 ---> 8 FeS
135
What is a decomposition reaction?
Decomposition- A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:
AB ---> A + B 2 H2O ---> 2 H2 + O2
136
What is a single displacement reaction?
Single displacement: This is when one element trades places with another element in a compound. These reactions come in the general form of:
A + BC ---> AC + B Mg + 2 H2O ---> Mg(OH)2 + H2
137
What is a double displacement reaction ( aka metathesis reaction)
Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:
AB + CD ---> AD + CB Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3
138
What are the steps to balancing equations?
1) balance the number of carbons
2) balance the number of hydrogens
3) balance the number of oxygens
4) balance any remaining atoms
5 if you need to you can multiply by decimals like 1.5 or something
6) if you do multiply by a decimal remember to go back in and multiply all the coefficients because you can have decimals as coefficients
7) make sure you check your work to see if both sides are balanced
139
Le Cs principle
If, for example, you removed C as soon as it was formed, the position of equilibrium would move to the right to replace it. If you kept on removing it, the equilibrium position would keep on moving rightwards - turning this into a one-way reaction.
140
What would happen if you changed the conditions by increasing the pressure?
According to Le Chatelier, the position of equilibrium will move in such a way as to counteract the change. That means that the position of equilibrium will move so that the pressure is reduced again.
Pressure is caused by gas molecules hitting the sides of their container. The more molecules you have in the container, the higher the pressure will be. The system can reduce the pressure by reacting in such a way as to produce fewer molecules.
141
What would happen if you changed the conditions by decreasing the pressure?
A+2B----- C+D
The equilibrium will move in such a way that the pressure increases again. It can do that by producing more molecules. In this case, the position of equilibrium will move towards the left-hand side of the reaction.
142
What happens if there are the same number of molecules on both sides of the equilibrium reaction?
In this case, increasing the pressure has no effect whatsoever on the position of the equilibrium. Because you have the same numbers of molecules on both sides, the equilibrium can't move in any way that will reduce the pressure again.
143
What would happen if you changed the conditions by decreasing the temperature?
A + 2B ----- C + D forward reaction is exothermic deltH= -250
Suppose the system is in equilibrium at 500°C and you reduce the temperature to 400°C. The reaction will tend to heat itself up again to return to the original temperature. It can do that by favouring the exothermic reaction.
144
Le C with temp
Increasing the temperature of a system in dynamic equilibrium favours the endothermic reaction. The system counteracts the change you have made by absorbing the extra heat.
Decreasing the temperature of a system in dynamic equilibrium favours the exothermic reaction. The system counteracts the change you have made by producing more heat.
145
what is the atomic weight?
This is the average of the atomic masses of the different isotopes. Like carbon 12 and Carbon 14 ect. This is the number that refers to grams per mole.
146
What is the molecular weight?
This is like atomic weight but is now a molecule. So you would add up each individual atomic mass in that molecule.
147
what is the molar mass?
The molar mass is the mass of one mole of something. This can relate to atoms and molecules. So for carbon 1 mole of a cabon weighs 12g. Or 1 mole of CO weights 28 grams.
148
What is Avogardos number?
This is 6.022*10^23. This number refers to how many molecules, ions, atoms ect. So if we have 1 mole of carbon this means that we have 6.022*10^23 carbon atoms. And the weight of that is 12 grams. Same goes for molecules if we have one mole of CO we have that many molecules of CO and that many molecules has a mass of 28 grams.
149
What is molarity?
Molarity = moles/L So if HCl and it has a molarity of 2.5. This means that for every liter there is 2.5 moles of HCl, or 2.5* 6.022*10^23 molecules of HCl
150
If we have 1 mol of carbon, how many carbon atoms is that?
6.022*10^23
151
If we have 1 mole of CO. how many grams does 1 mole of CO weigh?
28 grams
152
If we are trying to solve for the limiting reagent, what are the steps?
The limiting reagent is the reagent that will run out first when a reaction occurs
1) Balance the equation
2) convert reagents (reactants) to moles
3) Compare the number of moles you have to the number of miles required to run one cycle of the reaction, as indicated by the coefficients.
Say you have C3H8 + 5O2 ----- 3CO2 + 4H2O
we have 32 g of O2 and 11 g of C8H3
2) convert these to moles O2 = 1 mol and C8H3 = .25 mol
3) then you need to look at the balanced equation and say when C3H8 reacts with O2. Its a five to one ratio. So for every 1 mol or (6.022*10^23 molecules) of C3H8, 5 moles of O2 (or about 30 * 10^23) will react. So set it up as a conversion factor
you have .25 moles C8H3 (5 moles O2/ 1 mole C8H3) this will give you the amount of moles. Then compare this to the other mole values.
153
Limiting reagent altius example.
combustion of methane CH4 + 2O2 ---- CO2 + 2H2O
Suppose you have 1.5 moles of O2 and only 1.0 moles of methane. Because you need two moles of O2 to react with one mole of methane, you will run out of O2 first and it is therefor your limiting reagent. Even though you have more moles of O2 than you do of methane.
154
What's the definition of theoretical yield, actual yield, and percent yield?
The theoretical yield(in grams) of a reaction is the amount of product that would be formed if the reaction went to completion. You can solve for this by taking the amount of moles from the limiting reagent and converting this to grams using the final products molecular mass.
-Actual yield would be the actual amount in grams that you actually got when performing the experiment and weighing after you're done with the experiment. You can then find the percent yield by taking the actual yield divided by the theoretical yield to find the percent yield to see how accurate you did the experiment.
155
What are two ways that you can increase the yield of your experiment?
1) Start with more reactants
2) Shift the equilibrium to the right using one of the action of Le Chateliers principle. This includes one of the most common methods and that is removing products as they are formed. By doing so you force the reaction into a constant state of "catch up" and will continue to try and reach equilibrium.
156
Will adding more reactants increase the overall quantity of the yield and the percent yield?
It will increase the overall quantity but not the percent yield. You must add more of the limiting reagent too in order to increase the overall quantity.
157
When asked to predict the species that will require the most oxygen to combust what should you do?
Add 1.0 for each carbon and subtract 0.5 for each oxygen. The higher the resulting number the more oxygen necessary for full combustion. This is not NOT the actual number of moles required- it's only a ranking system.
158
Which requires the most oxygen to combust, propane, propanol, propanoic acid?
Propane
159
Define equilibrium conceptually?
When the forward and reverse reaction are happening at equal rates. This doesn't mean the concentrations on each side are equal however
160
What's equation for the equilibrium constant Keq? And are pure liquids and pure solids included in this equation?
Keq = (C)^c (D)^d / (A)^a (B)^b Each of these are raised to the coefficient which in front of each in the balanced equation.
No!
161
How does each of the following effect equilibrium? Catalyst, increased temp, lowering the Ea, stabilizing the transition state, addition of reactants and products?
A catalyst will have no effect on equilibrium, besides speeds up the rate of a reaction reaching equilibrium, Lowering the Ea is basically the same thing as adding a catalyst, if you add products that will shift the equilibrium to the left and vice versa for addition to the reactants. Temperature will affect the equlibrium depending on if the reaction is endo or exothermic.
162
Le Cs principle
The reaction will favor the side which relieves its stress. So if you have A+ B + heat --- C+ D and you add heat it will move to the right to try and relieve that heat and find its way back to equilibrium
163
When do you use the reaction quotient and the Keq?
If Q>K what does the mean?
If Q
You use the Keq when the reaction has already reached equilibrium. You use the Reaction Q equation when the reaction hasn't reached equilibrium yet.
Q>K the reaction will proceed to the left meaning a higher concentration of products
Q
164
Why aren't covalent compounds good conductors?
Because the electrons in the outer most shell are shared by the other atom. Covalent compounds are only good conductors unless they are good electrolytes. Even then it's the ions that are good conductors not the molecule itself.
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