Topic 9 Kinetics 1

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 the economic benefits of the use of catalysts in industrial reactions?

Answer 14

Catalysed reactions can occur at lower temperature so less fuel needed therefore fewer emissions from fuels.
Catalysed reaction enables use of an alternative process with higher atom economy so fewer raw materials are needed and less waste products are produced

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

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

Question 18

What happens to the Boltzman Curve when temperature is increased?

Answer 18

Peak shifts to the right
Lower peak
Bigger area above activational energy

Question 19

When are intermediates are formed

Answer 19

When you use homegenous catalysts

Question 20

What happens to the Boltzman Curve when a catalyst is used

Answer 20

Graph stays the same
Activation energy shifts to the left