Finding order from intial rates and conc. time data

Question 1

What is initial rate?

Answer 1

The instantaneous rate at the start of the reaction

Question 2

How do you calculate initial rate from a table?

Answer 2

Compare 2 experiments where the conc, had changed (preferably without a different reactant also changing), work out the rate in comparison with how initial rate changes, then see if no effect, same change, or change to the power of 2

Question 3

How do you find the value for k?

Answer 3

1. Rearrange the rate equation for k
2. Choose the values for any one of the experiments in the data table
3. Substitute these values for [ ] and rate into the rearranged expression

Question 4

Why do other reactants need to be in excess when the order of reaction is being measured?

Answer 4

The rate is only being measured over a short period of time so the change in concentration of other reactants will not have a significant impact on rate

Question 5

How do you determine order of reaction using a graph?

Answer 5

1. Plot a graph of conc./time
2. Find rate at different concentrations by drawing a tangents and calc. gradients
   Plot a graph of rate vs conc. and observe shape

Question 6

What is half-life?

Answer 6

The time taken for the concentration of a reactant to decrease by half

Question 7

How do you use half-lives to calculate order of reaction?

Answer 7

Work out to time for the conc. of a reactant to half. If it stays constant, this is 1st order

Question 8

What is the equation to find k of a 1st order reaction of a conc./time graph?

Answer 8

Find half-life and k = ln 2 / t x 0.5 (t = half-life)

Question 9

What is the equation to find k of a 0 order reaction of a conc./time graph?

Answer 9

K = gradient

Question 10

What is the equation to find k of a 2nd order reaction of a conc./time graph?

Answer 10

Find the rate at a particular concentration from the gradient of the tangent, substitute values into the rate equation

Question 11

What is the equation to find k of a 0 order reaction of a conc./rate graph?

Answer 11

K = ‘y-intercept’

Question 12

What is the equation to find k of a 1st order reaction of a conc./rate graph?

Answer 12

K = gradient

Question 13

What is the equation to find k of a 2nd order reaction of a conc./rate graph?

Answer 13

Pick a point on the graph and substitute values into the rate equation (or re-plot a rate vs graph and find gradient)