Module 3 - Reaction Rates

Question 1

What is the equation used to
calculate rate?

Answer 1

Rate = change in concentration / time

Question 2

What is the unit for rate of
reaction?

Answer 2

mol dm-3 s-1

Question 3

What must particles do in
order to react?

Answer 3

Collide with sufficient energy (activation
energy) and the correct orientation

Question 4

Do most collisions result in a
reaction?

Answer 4

No

Question 5

What are the factors that affect
rate of reaction?

Answer 5

● Temperature
● Pressure
● Concentration
● Surface area
● Catalyst

Question 6

What is the effect of increasing
temperature on rate of
reaction? why?

Answer 6

Increasing temperature → increased rate of reaction
Much higher proportion of particles have energy
greater than the activation energy → many more
successful collisions per second →increased rate

Question 7

What is the effect of increasing
concentration/pressure on rate
of reaction and why?

Answer 7

Increased concentration/pressure → increased rate of
reaction
There are more particles in a given volume → more frequent
successful collisions → increased rate

Question 8

What are the variables in an
experiment that can be
monitored to calculate the rate
of reaction?

Answer 8

● Concentration of reactant or product
● Gas volume of products
● Mass of substances formed

Question 9

How to calculate rate from a
concentration time graph?

Answer 9

Draw a tangent
Work out the gradient of the tangent using the
equation
Gradient = change in y / change in x

Question 10

What is a catalyst?

Answer 10

A substance which increases the rate of
reaction but is not used up in the
reaction

Question 11

How do catalysts work and
how do they increase the rate
of reaction?

Answer 11

They provide an alternate reaction pathway (with a
lower activation energy)
Due to lower activation energy, more particles have
energy > activation energy, so more frequent
successful collisions, so increased reaction rate

Question 12

What does homogeneous
catalyst mean?

Answer 12

A catalyst that is in the same phase as
the reactants.
Eg. liquid catalyst mixed with liquid
reactants

Question 13

What does heterogeneous
catalyst mean?

Answer 13

Catalyst used in the reaction is in
different phase to the reactants
Eg. gaseous reactants passed over solid
catalyst

Question 14

What are catalytic convertors?

Answer 14

They are present in vehicles to reduce
toxic emission and prevent
photochemical smog

Question 15

Define activation energy

Answer 15

The minimum energy that particles must
collide with for a reaction to occur

Question 16

Name some important
features of Boltzmann
distribution (5)

Answer 16

● Area under the curve = total number of molecules
● Area under the curve does not change when conditions
alter
● The curve starts at the origin
● Curve does not touch or cross the energy axis
● Only the molecules with energy greater than activation
energy can react

Question 17

What are the axis in a
Boltzmann distribution?

Answer 17

X axis - energy
Y axis - number of molecules with a
given energy