rates and equilibria

Question 1

rate equation

Answer 1

rate = k [A]^m [B]^n
where [ ] is the equilibrium concentration and m/n is the order

Question 2

order of 0

Answer 2

increase in concentration has no effect on rate of reaction

Question 3

order of 1

Answer 3

increase in concentration and rate are directly proportional

Question 4

order of 2

Answer 4

concentration and rate have a squared relationship

Question 5

half-life

Answer 5

the time taken for the concentration of a reactant to decrease by half

Question 6

k in terms of t1/2

Answer 6

k = ln 2 / t1/2

Question 7

rate-determining step

Answer 7

slowest step of a reaction mechanism of a multi-step reaction

Question 8

how to find the rate-determining step

Answer 8

the rate equation gives the species and their quantities in the rate-determining step

Question 9

activation energy

Answer 9

minimum energy required to start a reaction by breaking bonds in the reactants

Question 10

use of arrhenius equation on a graph

Answer 10

ln k = -Ea/R x 1/T + ln A
y-intercept gives ln A
gradient gives -Ea/R

Question 11

le chatelier’s principle

Answer 11

when a system in dynamic equilibrium is subjected to a change in conditions, the position of equilibrium shifts to minimise the effect of the change

Question 12

the equilibrium constant, Kc

Answer 12

Kc = [C]^c[D]^d / [A]^a[B]^b
where the lower case letters are the balancing numbers

Question 13

homogenous equilibrium

Answer 13

all species are in the same state

Question 14

heterogenous equilibrium

Answer 14

species are in different states

Question 15

significance of Kc values

Answer 15

Kc < 1 equilibrium shifts left
Kc > 1 equilibrium shifts right

Question 16

the equilibrium constant, Kp

Answer 16

Kp = p(C)^c x p(D)^d / p(A)^a x p(B)^b
where p is the partial pressure

Question 17

mole fraction

Answer 17

mole fraction of A = moles of A / total moles

Question 18

partial pressure

Answer 18

partial pressure = mole fraction x total pressure

Question 19

rate of reaction

Answer 19

change in concentration of reactant or product per unit time

Question 20

collision theory

Answer 20

molecules must collide with each other with energy greater than or equal to activation energy, with the correct orientation

Question 21

effect of increasing pressure on rate of reaction

Answer 21

gas molecules are pushed closer together
more gas molecules per unit volume
more frequent successful collisions
rate increases

Question 22

effect of increasing temperature on rate of reaction

Answer 22

kinetic energy of molecules increases
a higher proportion of molecules have energy greater than or equal to activation energy
more frequent successful collisions
rate increases

Question 23

types of catalysis

Answer 23

heterogenous catalysis - catalyst is in a different physical state than the reactants
homogenous catalysis - catalyst is in the same physical state as the reactants

Question 24

effect of a catalyst

Answer 24

increases the rate of reaction by providing an alternate reaction pathway with a lower activation energy

Question 25

dynamic equilibrium

Answer 25

rate of forward and reverse reactions are equal system is closed concentration of reactants and products does not change

Question 26

effect of pressure on position of equilibrium

Answer 26

if pressure is increased, the position of equilibrium will shift to the side with the fewest moles of gas (and vice versa)

Question 27

effect of temperature on position of equilibrium

Answer 27

in de exothermic | L | R endothermic | R | L

Question 28

effect of catalyst on position

Answer 28

catalyst increases the rate of the forward and reverse reaction equally so has no effect on the position of equilibrium