chemical kinetics 1

Question 1

what is the rate of reaction

Answer 1

change in concentration over the change in time

Question 2

what two things are necessary for a reaction to occur

Answer 2

particles must collide with the correct orientation
particles must meet the activation energy

Question 3

what 5 factors affect rate of reaction

Answer 3

concentration/pressure
pH
surface area
temperature
catalyst

Question 4

what is the correct orientation of particle collision

Answer 4

delta + should be facing delta -

Question 5

define activation energy

Answer 5

minimum investment of energy that must be supplied to enable bonds in reactants to stretch and break as new bonds are formed

Question 6

why does increasing the concentration increase the rate of reaction

Answer 6

more molecules per unit volume so a greater chance of collision - more collisions per unit time

Question 7

effect of increased surface area on rate

Answer 7

more collisions per unit time

Question 8

effect of increasing temperature on rate of reaction

Answer 8

increases the kinetic energy of the molecules
results in more frequent collisions and collisions have higher energies
more successful collisions per unit time

Question 9

effect of pressure on rate of reaction

Answer 9

more molecules per dm3
greater chance of collisions
more collisions per unit time

Question 10

what doe the Maxwell Boltzmann diagram show

Answer 10

number of molecules having particular kinetic energies at a constant temperature

Question 11

what does an increase in temperature do to the peak on a Maxwell Boltzmann diagram

Answer 11

moves to the right
there are more molecules with the activation energy
area under the curve must remain constant

Question 12

define a catalyst

Answer 12

a substance that speeds up the rate of reaction by providing an alternative route or mechanism with a lower activation energy

Question 13

effect of catalyst on rate of reaction

Answer 13

catalysts lower the activation energy
more particles have reached the activation energy
more successful collisions per unit time

Question 14

method for measuring changes in a volume of gas

Answer 14

1 use a gas syringe and record volumes at frequent intervals
2 plot volume vs time graph
3 tangent to the steepest part to find initial rate
4 repeat with other concentrations

Question 15

method for measuring colour change (colorimetry)

Answer 15

1 choose filter of complimentary colour and calibrate colorimeter against water
2 mix reagents
3 record absorbance of transmission at frequent time intervals
4 region of most rapid change = initial rate
5 repeat with other concentrations

Question 16

what is a first order rate concentration graph

Answer 16

upwards straight diagonal

Question 17

what is a second order rate concentration graph

Answer 17

upwards curve

Question 18

what is a first order concentration time graph

Answer 18

downwards straight diagonal

Question 19

what is a second order concentration time graph

Answer 19

downwards curve

Question 20

what is a zero order rate concentration graph

Answer 20

parallel to x axis

Question 21

what is a zero order concentration time graph

Answer 21

downwards straight diagonal

Question 22

example of a rate equation

Answer 22

rate = k[A]m[B]n
where m and n are the order of reaction with respect to each chemical

Question 23

what is k

Answer 23

the overall rate constant

Question 24

what is the overall order of the reaction

Answer 24

sum of the orders of the concentrations of the reactants

Question 25

define half life of a chemical reaction

Answer 25

the time taken for the concentration of a component to decrease to half its initial value

Question 26

which order of reaction has a constant half life

Answer 26

first order

Question 27

which order is it if half lives become longer (not constant)

Answer 27

an order greater than first

Question 28

define rate constant

Answer 28

relates to the rate of a chemical reaction at a given temperature to the product of the concentrations of reactants

Question 29

define order of reaction

Answer 29

the power to which the concentration of that reactant is raised in the rate equation

Question 30

explain in terms of collision and energy, why lowering the temperature decreases the rate of reaction (2 marks)

Answer 30

particles have less kinetic energy
less particles meet the activation energy
less successful collisions per unit time

Question 31

state how a catalyst increases the rate of a chemical reaction (1 mark)

Answer 31

decreases the activation energy
more particles are able to react under the same conditions