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Chemistry > Textbook Unit 1.5 > Flashcards

Textbook Unit 1.5 Flashcards

(55 cards)

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1
Q

what is reaction rate

A

how quickly it happens
- defined as change in concentration/amount of a reactant or product over time

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2
Q

what is the formula to find the ror

A

amount of reactants used/products formed

divided by

time

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3
Q

what are particles in gas and liquids always doing

A

moving and colliding with each other

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4
Q

when does a collision between the moving particles in liquids and gases occur (collision theory)

A

when the conditions are right, a reaction between two particles will take place

  • they need to collide in the right direction (facing each other correctly)
  • they collide with atleast a certain minimum amount of kinetic energy
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5
Q

what is the minimum amount of kinetic energy that particles need to react also called

A

Activation energy

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6
Q

why do particles need activation energy

A

to break their bonds and start a reaction ( usually shown in enthalpy profile diagram)

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7
Q

what is the progress of reaction in an enthalpy profile diagram

A
  • bonds within each particle are being stretched
  • if particles have enough energy, bonds will break
  • the activation energy is the energy barrier the particles have to overcome
  • reaction done
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8
Q

how can you give particles extra energy (for high activation reactions)

A

by heating them

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9
Q

What is a Maxwell-Boltzmann Distribution Graph

A

when you plot a graph of the numbers of molecules in a gas with different kinetic energies

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10
Q

Describe a Maxwell - Boltzmann distribution graph

A
  • area under MBD curve is equal to the total number of molecules
  • curve starts at (0,0) because no molecules have zero energy
  • molecules near the end of the graph have more kinetic energy than activation energy so they are the only ones that can react
  • peak of the curve represents the most likely energy of any single molecule
  • the mean energy of all the molecules is abit to the right of the peak
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11
Q

what happens if you increase the temperature of a reaction

A

the particles will on average have more kinetic energy and will move faster
- a greater proportion of mols will have atleast the activation energy and be able to react which changes the curve of the mbd graph moving the curve towards the right

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12
Q

what is a reason increasing temperature makes a reaction faster

A

at higher temps, the molecules fly about faster and theyll collide more often

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13
Q

why does small increases in temp lead to large increases in reaction rate

A

bc both effects of more collisions and more energetic collisions are happening at one time

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14
Q
A
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15
Q

how does increasing concentration increase ror

A

if increase reactants in solution, particles become more closer together on average
- bc more closer, collide more often, so more chances to react with each other

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16
Q

how does increasing pressure increase ror (usually gases)

A

increasing pressure, more closer gas particles, more likely to collide, collisions are more frequent so ror inscreases

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17
Q

how do catalysts increase the ror

A
  • dont get used up in reaction so only need a little
  • they do take part in reaction but are remade at the end
  • catalysts only work on a single reaction
  • bc catalysts make same amount of product faster nd with less heat, saves lots of money in industrial processes
  • catalysts lowers the activation energy, meaning more particles with enuf energy to react when they collide, does this by allowing reaction to go thru a different route so more particles react
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18
Q

give me the catalyst definition

A

A catalyst is a substance that increases ror by providing an alternative reaction pathway with a lower activation energy, the catalyst is chemically unchanged at the end of the reaction

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19
Q

how can you measure ror

A

by how fast the reactants are used up or how fast products are formed

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20
Q

how many ways are there to measure ror

A

3

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21
Q

what is the first method to measure ror

A
  • TIMING HOW LONG PRECIPITATION TAKES TO FORM
  • use this method when product is a precipate (clouds a solution)
  • can watch a mark and see how long it takes to be obscured (hidden)
  • if SAME observer uses SAME mark each time, can compare the rates of reaction bc roghtly same amount of preicipitation is fromed when mark becomes obscured
  • HOWEVER method is subjective, diff ppl might not agree on the exact moment it disappears
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22
Q

what is the second method to measure ror

A
  • MEASURING A DECREASE IN MASS
  • if one or more products is a gas, can measure rate of formation using a mass balance
  • as gas is given off, the mass of reaction mixture decreases
  • method is accurate and easy to do, but releases gas into atmosphere so usually done in a fume cupboard
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23
Q

what is the third method to find ror

Study These Flashcards
A
  • MEASURING THE VOLUME OF GAS GIVEN OFF
  • involved a gas syringe to measure the volume of gas being produced
  • only use this method when one or more products is a gas
  • gas syringes usually gives volume to nearest 0.1cm3 so method is accurate
24
Q

what can reversible reactions reach

Study These Flashcards
A

dynamic equilibrium

25
when does the forward reaction slow down
as the reactant get used up
26
when does the reverse reaction speed up (reversible reactions)
when more product is formed
27
what happens during reversible reactions
- the forward reaction ends up going at the same rate as the backwards reaction so amount of products and reactants wont be changing - as if nothing is happening (dynamic equilibrium)
28
when can dynamic equilibrium happen
- only in a closed system (means nothing is going in or out) - during equlilibrium the concentration of reactants and products stay constant
29
what happens if you change the temp, pressure or concentration of a reversible reaction
you'll end up with different amounts of reactants and products at equilibrium
30
what happens if position of equilibrium moves left
more reactants are produced
31
what happens if the position of equilibrium moves to the right?
more products will be produced
32
what does le chatelier's principle tell us ab how the position of equilibrium changes if a condition changes?
if a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change e.g. if temp raised, position of equilibrium changes to cool it down if pressure, concentration raised, poe changes to reduce it again
33
what is le chataliers principle used for
to work out what effect changing the concentration, pressure or temp will have on the poe (only applies to homogeneous equilibria - all solutions in same state)
34
what is le chataliers principle about concentration
- if increase the concentration of reactant, equilibrium tried to get rid of extra reactant - does this my baking more product so e shifts to right - if products conc increased, shifts to left to make more reactions (now reverse reaction is faster - if decreasing conc then opposite
35
what is le chataliers principle about pressure (only affects gas)
- increase pressure shifts equilibrium to side with less gas mols bc this reduces pressure - decreasing pressure pushes e to side with more, this increases pressure
36
what is le chataliers principle about temperature
increase temp means e shifts to side of endorthermic reaction (positive delta side) to absorb the heat - decrease temp means e shifts to the exothermic side ( negative delta) so it can produce more heat
37
how do catalysts affect the position of equlibrium
catalysts have no effect on the poe - they cant increase yield but they do help equilibrium to be reached faster
38
give me an example of how a reaction is chosen in industry (ethanol) ( 6 points)
- ethanol is produced by a reversible exo reaction between ethene and steam - r is carried out with temp 300 degrees and pressure of 60 - 70 atmospheres, nd with a catalyst of phosphoric acid - bc exo, low temp favours forward reaction, so ethene and steam is converted into more ethanol (now a better yield) - low temp means slower ror, so 300 degrees is a compromise for a reasonable yield and a faster reaction - high pressure shifts e to side with fewer molecules, which favours forward reaction, high pressure makes reaction faster but too high pressure needs high costs, high quality equipment e.g. pipes and containers to withstand pressure - so 60 - 70 atmospheres is a compromise - gives reasonable yield for lowest possible cost
39
Kc = equilibrium constant how can you work it out
if you know the molar conc of each substance in equilibrium (LEARN EQUATION SEPARATELY)
40
the value of the equilibrium constant (Kc) is only valid ...
for one temperature
41
why is the Kc only valid for one temp
bc if temp changes, equilibrium concentrations of products and reactants so e constant will change - if temp change means more products = Kc will rise - if temp change means reactants = Kc will decrease - catalysts dont affect it
42
whats a redox reaction
if electrons are transferred in a reaction e.g. when sodium and chloride is made
43
what is it called if theres an electron gain or loss
loss - oxidation gain - reduction - happens simultaneously hence why called redox reaction
44
what does an oxidising agent and a reducing agent do
(poor) oxidising agent - accepts electrons and gets reduced (rich) reducing agent - donates electrons and gets oxidised
45
what does the oxidising state of an element tell you
total numbers of electrons it has donated or accepted if donated 1 = +1 charge to element if accepted 1 = -1 charge to element
46
what can roman numerals show
oxidation states
47
what do ionic half equations show and why
oxidation or reduction bc they are constantly being lost or gained in half equations
48
can you combine half equations for different oxidising or reducing agents
yes you can make full equations for redox reactions
49
what are the uncombined elements oxidation state
0
50
elements bonded to an element with same atoms, have an oxidation state of what?
0
51
what is the oxidation state of a simple monatomic ion (one atom)
the same as its charge (+1 or -1)
52
in compound ions what is the overall oxidation state
the ion charge (have to add charges of all atoms)
53
sum of oxidation state for a nuetral (0 change) compound is wat?
0
54
what is the oxidation state of combined oxygen
almost always -2 except - in peroxides where its -1 - in H2 where its 0
55
what is the oxidation state of combined hydrogen?
+1 except - in metal hydrides where its -1 - and in H2 (where its 0)

Chemistry (6 decks)

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