rates + equilibrium

Question 1

order of reaction definition

Answer 1

shows the extent to which the concentration of a reagent affects the rate of reaction
the power to which the concentration of a reagent is raised to in the rate equation

Question 2

what does it mean if a reagent is 0 order

Answer 2

the rate is unaffected by changes in concentration of that reagent

Question 3

what does it mean if a reagent is 1st order

Answer 3

if the concentration changes, the rate will change by the same factor/amount

Question 4

what does it mean if a reagent is 2nd order

Answer 4

if the concentration changes, the rate will change by the square of that amount

Question 5

rate constant k definition

Answer 5

the constant of proportionality in the rate equation

Question 6

what affects rate constant k

Answer 6

temperature and catalysts, not concentration or pressure

Question 7

how does temperature affect k

Answer 7

increase in temperature increases k value
- high temp = more kinetic energy = more successful collisions = high rate = larger k value

Question 8

how do catalysts affect k

Answer 8

catalysts increase k
- catalyst = faster rate = larger k value

Question 9

what does a very high k value mean

Answer 9

fast reaction rate

Question 10

what does a very small k value mean

Answer 10

slow reaction rate

Question 11

what is the overall order of a reaction

Answer 11

the sum of all orders of reagents taking part in reaction

Question 12

half life definition

Answer 12

how long it takes for reactant concentration to half

Question 13

what can be found from concentration-time graphs of a reaction

Answer 13

the order of the reactant can be found by measuring the half life

• if half life gets smaller = 0 order
• if half life stays constant = 1st order
• if half life increases = 2nd order

Question 14

which step of a reaction is the rate determining step

Answer 14

the slowest step, as a reaction can only go as fast as the slowest part of a reaction

Question 15

if the gradient of a first order rate-conc graph is measured what does this give

Answer 15

the value of k
this is because rate = k[reactant] so as conc = x axis and rate = y axis gradient = k

Question 16

when determining composition of a reaction mixture, why is the analysis of a physical property preferable to a chemical analysis

Answer 16

• measuring the change in a physical property will not interfere with reaction
• chemical analysis means the reaction must be stopped so analysis can take place to determine composition

Question 17

suggest 2 physical properties that could be measured + how

Answer 17

colour change of gases or solutions
- this could be done using a colorimeter calibrated with known concentrations of the coloured substance

release of gas
- this could be done with a gas syringe or by measuring loss of mass

Question 18

what is the rate equation

Answer 18

rate = k[reactants]^order

Question 19

what is the half life equation

Answer 19

k = ln(2) / half life

half life known as t 1/2

Question 20

what is the arrhenius equation

Answer 20

k = Ae^(- Ea / R T)
rearranged to
lnk = -Ea / R T + lnA

Question 21

what are all the variables in arrhenius equation

Answer 21

k = rate constant
A = pre exponential factor (aka arrhenius constant)
e = eulers constant
Ea = activation energy (Jmol-1)
T = temp (K)
R = gas constant

Question 22

what 3 types of reactions does the arrhenius equation describe

Answer 22

• reactions involving gases
• reactions occurring in solution
• reactions occurring on the surface of a catalyst

Question 23

mole fraction definition

Answer 23

the fraction of the total number of moles that each substance in a reaction is responsible for - the amount of moles of a component divided by total number of moles in the mixture

Question 24

partial pressure definition

Answer 24

the proportion of the total pressure that each chemical in a reaction is responsible for - the amount of pressure that would be exerted by a gas within a mixture if it occupied the same volume on its own at the same temp

Question 25

what types of substance can be included in kc and kp calculations

Answer 25

ones in gaseous or aqueous states
no solids or liquids!

Question 26

partial pressure p(X) equation

Answer 26

p(X) = total pressure x mole fraction

Question 27

homogenous equilibria definition

Answer 27

all species are in the same state

Question 28

heterogenous equilibria definition

Answer 28

all species aren’t in the same state

Question 29

what factors affect kc and kp

Answer 29

only temperature

concentration, pressure and catalysts have no effect

Question 30

why does concentration/pressure not have an effect on kc and kp

Answer 30

changes in pressure or concentration change the position of the equilibrium, but as this affects concentration of reacting substances, the position of equilibrium moves back to minimise the effect of this change, overall no effect

Question 31

why do catalysts have no effect on kc and kp

Answer 31

catalysts increase rates of forwards and backwards reactions equally so no effect

Question 32

how does temperature affect kc and kp

Answer 32

for exothermic reactions, increasing temp = decreasing kc/kp as this favours the opposite reaction, so decreased products/increased reactants = decreased kc/kp

for endothermic reactions increasing temp = increasing kc/kp as this favour the forward reaction, so increased products/decreased reactants = increased kc/kp