3.2.2 reaction rates

Question 1

Collision theory

Answer 1

Reactions can only occur when collisions take place between particles that have enough energy

Energy is needed to break the relevant bonds in reactant molecules

Minimum energy is activation energy

Question 2

Activation energy

Answer 2

Minimum energy which particles need to collide to start a reaction

Question 3

Effect of increasing concentration or pressure

Answer 3

There are more particles per unit volume so the particles collide with a greater frequency

Higher frequency of effective collisions

Question 4

Measuring reaction rates

Answer 4

Change in concentration of a substance in unit time

Mol dm-3 s-1

Gradient = rate of reaction

Initial rate = rate at the start of the reaction where it is fastest

Draw a tangent

Question 5

Catalyst

Answer 5

Increase reaction rates without getting used up

Do this by providing alternative route with a lower activation energy so more molecules have energy above activation energy

Question 6

Heterogenous catalyst

Answer 6

In a different phase from the reactants

Usually solids whereas reactants are gaseous or in solution

Reaction occurs at surface of the catalyst

Question 7

Homogeneous catalyst

Answer 7

Same phase at the reactants

Reaction proceeds through intermediate species

Question 8

Benefits of catalysts

Answer 8

Speed up the rate of reaction - lower temperatures and pressures may be used

Saves energy costs > fewer co2 emissions from burning of fossil fuels

Less waste products

Question 9

Measuring change in volume of gas

Answer 9

Connect gas syringe to tube going into conical flask