4.2.4&4.2.5: Initial rates method & Clock reactions

Question 1

What is needed to work out the rate equation?

Answer 1

the orders of reaction

Question 2

How to work out the orders of reaction?

Answer 2

determined experimentally

whilst monitoring the initial rate of reaction as you change the conc. of one of the reactants

Question 3

Finding the initial rate of reaction using a graph

Answer 3

concentration-time graph

calculate gradient of curve at t=0

Question 4

Clock reactions

Answer 4

measure how the time taken for a set amount product to form from as you vary the concentration of reactants

Question 5

Assumptions for the clock reaction

3

Answer 5

1. Temperature stays constant
2. When the endpoint is seen, the reaction hasn’t proceeded too far
3. The conc. of each reactant doesn’t change significantly over the time period of your clock reaction

Question 6

Most famous example of a clock reaction

Answer 6

iodine clock reaction

Question 7

Iodine clock reaction equation

Answer 7

H2O2 + 2I- + 2H+ > 2H2O + I2

Question 8

Iodine clock reaction reactants

Answer 8

small amount of sodium thiosulphate solution and starch added to an excess of hydrogen peroxide and iodide ions in acid solution

Question 9

Role of starch in the iodine clock reaction

Answer 9

indicator

turns blue black in presence of iodine (I2)