3.2.2: 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 and 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 marks)

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