Topic 9- Kinetics

Question 1

What equation is used to calculate rate?

Answer 1

rate= change in concentration/time

Question 2

What is the unit for rate of reaction?

Answer 2

moldm-3s-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 factors affect the rate of reaction?

Answer 5

• temperature
• concentration
• catalyst
• pressure
• surface area

Question 6

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

Answer 6

increasing temperature –> increased rate of reaction because… a higher proportion of particles have energy greater than the activation energy –> more collisions per second –> increased rate

Question 7

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

Answer 7

increased conc/pressure= increased rate

there are more particles in a given volume –> more frequent 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 gradient of tangent using….
gradient=change in y/change in x

Question 10

What is a catalyst?

Answer 10

a substance which increases the rate of reaction but isn’t 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 alternative reaction pathway, with a lower activation energy
• due to lower activation energy, more particles have energy greater than the activation energy, so more frequent collisions and increased rate

Question 12

What does homogeneous catalyst mean?

Answer 12

a catalyst that is in the same phase as the reactants

Question 13

What does heterogeneous catalyst mean?

Answer 13

catalyst used in the reaction is in different phase to the reactants

Question 14

What are the economic benefits of using a catalyst in industrial reactions?

Answer 14

catalysed reactions can occur at lower temperatures so less fuel needed so fewer fuel emissions
enables use of an alternative process with a higher atom economy so fewer raw materials are needed and less waste products produced

Question 15

Define activation energy

Answer 15

the minimum energy required for particles to collide for a reaction to occur

Question 16

Name some important features of a Boltzmann distribution curve

Answer 16

• area under the curve= total number of particles
• area under the curve doesn’t change when conditions alter
• curve starts at the origin
• curve does not touch or cross the energy axis
• only the molecules with energy higher than the activation energy can react

Question 17

What are the axis in a Boltzmann distribution curve?

Answer 17

x-axis = energy
y-axis = fraction of molecules