1. Physical AS Flashcards
(117 cards)
1
Q
define relative atomic mass of an element
A
the average mass of an atom compared to one twelfth of the mass of one carbon-12 atom
2
Q
define relative molecular mass of a substance
A
The relative molecular mass of a substance is the weighted average of the masses of the molecules relative to 1/12 of the mass of a carbon-12 atom.
3
Q
what is the formula and charge for phosphate?
A
4
Q
what is the formula and charge for hydrogen carbonate?
A
HCO3 -
5
Q
what is the formula and charge of a carbonate ion?
A
CO3 2-
6
Q
what order do you balance the elements in combustion reactions?
A
C, H, O
7
Q
what do ionic equations show?
A
only the ions or other particles taking part in a reaction and not the spectator ions
8
Q
why is the percentage yield never 100%?
A
1)other reactions taking place simultaneously
2)the reaction does not go to completion
3)reactants or products are lost to the atmosphere
9
Q
what is the formula for percentage yield?
A
10
Q
how do you calculate which is the limiting/excess reagents?
A
1)the number of moles of each reactant should be calculated
2)the ratio of the reactants should be taken into account
3) the reactant leftover is in excess, the reactant which causes the reaction to stop once it is used up is the limiting reagent
11
Q
what is atom economy?
A
how many of the atoms used in the reaction become the desired product - the rest are wasted
12
Q
what is the equation for atom economy?
A
13
Q
why is the atom economy in addition reactions always 100%?
A
because all of the atoms are used to make the desired product
14
Q
at room temp what is the volume of 1dm3 of any gas?
A
24 dm^3
15
Q
what is the equation for working our moles of a gas?
A
16
Q
what two factors does the volume an ideal gas occupies depend on?
A
it’s pressure, it’s temperature
17
Q
volume is directly proportional to…
A
temperature
18
Q
what is the ideal gas equation?
A
PV=nRT
19
Q
what are the units for each of the letters of the ideal gas equation?
A
P= (pa)
V= (m^3)
R= (8.31 JK-1mol-1)
T= (K)
20
Q
how do you convert Celsius to kelvin?
A
+273
21
Q
what is the relative mass of an electron?
A
1/1836
22
Q
what is the symbol for atomic number?
A
Z
23
Q
what is the symbol for mass number?
A
A
24
Q
why do isotopes of the same element display the same chemical properties but different physical properties?
A
They have the same number of electrons in their outer shell, and electrons take part in chemical reactions therefore determine the chemistry of an atom.
25
why do isotopes have different physical properties?
the only difference in isotopes is the number of neutrons, which only add mass to the atom (as they are neutral). Therefore, isotopes have small differences in their mass and density.
26
define isotope
Isotopes are different atoms of the same element that contain the same number of protons and electrons but a different number of neutrons (different mass numbers, same atomic number)
27
why is the whole TOF apparatus kept under a vacuum?
To prevent any ions that are produced from colliding with molecules in the air
28
what are the 4 stages of TOF mass spectrometry?
Ionisation, Acceleration, Ion Drift, Detection
29
what are the two types of ionisation
electron impact and electrospray ionisation
30
what is electron impact ionisation used for?
for elements and substances which have a lower molecular mass
31
describe electron impact ionisation
1)sample vaporised
2)bombarded with high energy e^- from an e^- gun
3)1+ ion formed called molecular ions or M+ ions
32
give the equation for electron impact ionisation
X(g)--> X+ (g) + e-
33
what is electrospray ionisation used for?
for substances which have a higher molecular mass (soft ionisation technique)
34
Describe electrospray ionisation
1)sample dissolved in a volatile solvent
2)injected into mass spec using a hypodermic needle - produce a fine mist or aerosol
3) needle attached to high voltage power supply- particles ionised as sample injected
4)solvent evaporates and XH+ ions are attracted to the -vely charged plate
35
give the equation for electrospray ionisation
X(g)+H^+--> XH+(g)
36
describe acceleration
the 1+ ions formed are all accelerated to have the same kinetic energy, therefore their velocity will depend on their mass
37
Describe ion drift
the 1+ ions will pass through a hole in the negatively charged plate and move into the flight tube - their TOF will depend on their velocity
38
Describe detection
1)the 1+ ion will hit a -vely charged 'detector' plate, where they gain an e-
2)the gaining of the e- discharges the ion and causes a current to be produced
3)the detector plate is connected to a computer, which produces the mass spectrum
39
the size of the current at the detector is proportional to...
the abundance of the ions hitting the plate and gaining an e-
40
what is the equation for TOF?
41
what are the units for each letter?
KE (J), m (kg), v (m/s), t (s), d (m)
42
the lower the principal quantum number ...
the closer the shell is to the nucleus e.g. n=1 would be the first shell which is closest to the nucleus
43
the higher the principal quantum number...
the greater the energy of the shell and the further away from the nucleus
44
each principal quantum number has a fixed number of ...
e- which it can hold
45
how many e- can each principal quantum number hold?
n1 = 2
n2= 8
n3 = 18
n4 = 32
46
the principal quantum numbers are split into ...
sub shells which are split into s,p and d
47
the energy of the e- from s to p to d ...
increases
48
subshells contain one or more...
atomic orbitals
49
orbitals exist at specific energy levels and e-...
can only be found at these specific levels, not in between them
50
what is the max number of e- each orbital can hold?
2
51
how manty orbitals are there in each subshell?
52
the size of the orbitals increase with...
increasing shell number
53
what is the ground state of an atom?
the most stable electronic configuration which has the lowest amount of energy
54
which orbital is filled out first the 3d or 4s?
4s as it is higher in energy
55
which subshell do transition metals first lose electrons from ?
4s first then the 3d as 4s is lower in energy
56
why will e- occupy separate orbitals in the same subshell where possible?
to minimise repulsion and have their spin in the same direction
57
define ionisation energy (IE) of an element
the amount of energy required to remove one mole of e- from one mole of gaseous atoms to form one mole of gaseous ions
58
what are the units for IE?
kJ mol^-1
59
what four factors is the size of the 1st IE affected by?
1)size of the nuclear charge
2)distance of outer e- from the nucleus
3)shielding effect of inner e-
4)spin-pair repulsion
60
why does first IE increase across a period?
the nuclear charge increases, causing the atomic radius to decrease , shielding remains constant
61
why does B have a lower IE than Be?
B valence electron is in the 2p subshell which is further away from the nucleus than the 2s subshell, therefore it requires less energy to remove the e- from B
62
why does O have a lower 1st IE than N?
in oxygen there are two e- in the 2p orbital so the repulsion makes it easier for one of those e- to be removed
63
why is there a large decrease in IE between the last element in one period, and the first element in the next period?
1)increased distance between valence e- and nucleus- new shell added
2) increased shielding by inner e-
3) these 2 factors outweigh the increase in nuclear charge
64
why is it more difficult to remove an e- from a positive ion than a neutral atom?
the attractive forces increase due to decreasing shielding and an increase in the proton to e- ratio
65
why are ions arranged in a lattice structure?
ions are arranged in a regular repeating pattern so that +ve charges cancel out -ve charges, therefore the overall lattice is electrically neutral
66
how can you increase the strength of metallic attraction?
1)increasing the number of delocalised e- per metal atom
2)increasing the +ve charges on the metal centres in the lattice
3)decreasing the size of the metal ions
67
what makes metals malleable and ductile?
layers of +ve ions can easily slide over one another, as the e- do not belong to any particular metal atom so they can move with the layers of the +ve ions, maintaining the electrostatic forces and the metallic bonds are not broken
68
the most stable shape is adopted to...
minimise the repulsion forces
69
why do lone pair of e- repel the mot?
they have a more concentrated electron charge cloud and they are wider and closer to the central atom's nucleus
70
what bond angles and shape does trigonal bipyramidal have?
71
what bond and shape does octahedral have?
72
define electronegativity
the power of an atom to attract a lone pair of electrons towards itself in a covalent bond
73
what 3 things affect electronegatvity?
nuclear charge, atomic radius, shielding
74
can you put the following bonding in order of strength, starting from weakest? van der waals, ionic, hydrogen, metallic, pd-pd, covalent
75
when two atoms in a covalent bond have the same electronegativity the covalent bond is...
polar
76
which types of molecules experience pd-pd forces and why?
polar molecules as they have a permanent dipole
77
how does hydrogen bonding occur?
the hydrogen bonds to a lone pair on a F, O, N atom
78
is bond breaking endothermic or exothermic and why?
endothermic, because energy is required to overcome the attractive forces between atoms
79
is bond-forming endothermic or exothermic, and why?
exothermic, as energy is released from the reaction into the surroundings when new bonds are formed
80
define activation energy
the minimum amount of energy required for reactant molecules to have a successful collision and start the reaction
81
what does an exothermic graph look like?
82
what does an endothermic graph look like?
83
how do you identify the Ea on a graph?
the energy difference from reactants to transition state
84
how do you identify enthalpy change on a graph?
the energy difference from reactant to products
85
what do you label the x and y axis in an energy level diagram?
y axis - Energy (kJ mol-1)
x axis - extent of the reaction
86
define standard enthalpy change of a reaction and give the symbol
87
define standard enthalpy change of formation and give the symbol
88
define standard enthalpy change of combustion and give the symbol
89
define standard enthalpy change of neutralisation and give the symbol
90
what is the enthalpy of formation of an element in its standard state?
zero
91
how do you calculate standard enthalpy of formation using Hess' s Law when given enthalpy of formation data (diagram method)?
1)write balanced equation at the top , e.g. reactants then poroducts
2) write constituent elements at the bottom
3)draw arrows going up to the reactants and products
92
define enthalpy change of atomisation
the enthalpy change when one mole of gaseous atoms is from its elements under standard conditions
93
define bond dissociation energy
the amount of energy required to break one mole of a specific covalent bond in the gas phase is called bond dissociation energy
94
how do you calculate standard enthalpy of formation using Hess' s Law when given enthalpy of combustion data (diagram method)?
1)write the equation for the enthalpy change of formation at the top
2)write the combustion products at the bottom
3)draw arrows going down to the combustion products
95
96
97
what is the collision theory?
in order for a chemical reaction to take place the particles need to collide with each other in the correct orientation and with enough energy (Ea)
98
define catalyst
a substance that increases the rate of reaction without taking part in the chemical reaction by providing an alternative mechanism with a lower activation energy
99
define rate of reaction
100
what is a homogeneous catalyst?
that the catalyst is in the same phase as the reactants, e.g. the reactants and the catalysts are all in solution
101
what is a heterogenous catalyst?
that the catalyst is in a different phase to the reactants, e.g. the reactants are gases but the catalyst used is a solid
102
which way does the equilibrium shift if the concentration of the reactants increases?
to the left
103
which way does the equilibrium shift if the concentration of the products increases?
to the right
104
what effect do catalysts have on the position of the equilibrium?
None, they only cause a reaction to reach equilibrium faster
105
what is the only factor that can affect Kc value?
temperature
106
what is the only factor that can affect Kc value?
temperature
107
how can temp affect Kc value (endothermic reaction)?
in an endothermic reaction an increase in temp can increase the amount of products and decrease the amount of reactants, therefore the KC increases
108
*how can temp affect Kc value (exothermic reaction)?
in an exothermic reaction an increase temperature would mean the products decrease and the reactants increase so Kc decreases.
109
is Kc affected by a catalyst?why?
No, because a catalyst speeds up both the forward and reverse reactions at the same rate so the ratio of products and reactants stays the same.
110
what catalyst doe the contact process use?
vanadium(V) oxide
111
what are the 3 definitions for oxidation?
112
what are the 3 definitions of reduction?
113
what does the oxidation state of an atom tell you?
the charge that would exist on an individual atom if the bonding were completely ionic
114
what is an oxidising agent?
a substance that oxidises another atom or ion by causing it to lose electrons, however it gets reduced itself as it gains electrons, so the oxidation state decreases
115
what is a reducing agent?
a substance that reduces another atom or ion by causing it to gain electrons, however it gets oxidised itself as it loses electrons, so the oxidation state increases
116
when determining oxidation state which species will have the negative oxidation state?
the more electronegative one
117
what is a disproportionation reaction?
a reaction in which the same species is both oxidised and reduced
