8. Reaction Kinetics A2

Question 1

Rate equation

Answer 1

An equation that relates the rate of reaction to the concentration of reactants raised to the appropriate power

Question 2

Rate constant

Answer 2

Constant of proportionality for a given reaction at a given temperature

Question 3

Order of reaction

Answer 3

The power to which the concentration of a reactant is raised in the rate equation

Question 4

Half-life of a reaction

Answer 4

The time taken for the concentration of a reactant to halve

Question 5

Describe 2 ways of using these results to show the reaction is first order with respect to H2 (g) concentration. [3m]

Answer 5

Method 1

• plot a graph of concentration of H2 against time
• constant half-life shows it is 1st order

Method 2

• draw tangent AND determine gradient on conc-time graph
• plot a graph of rate against concentration of H2
• gives a straight line through the origin of graph

Question 6

Magnesium carbonate was heated in an open test-tube. It was difficult to see whether a thermal decomposition reaction took place. Explain why. [2m]

Answer 6

• CO2 gas produced is colourless, cannot be seen

- colour of solid (MgCO3 –> MgO) doesn’t change, remains white after heating