IB Chemistry HL

Revision Notes

16.2.2 Graphing the Arrhenius Equation

Graphing the Arrhenius Equation

Finding the Activation Energy

  • Very often, the Arrhenius Equation is used to calculate the activation energy of a reaction
  • A question will either give sufficient information for the Arrhenius equation to be used or a graph can be plotted and the calculation done from the plot

Using the equation:

  • Remember, it is usually easier to use the version of the Arrhenius equation after natural logs of each side have been taken

Using an Arrhenius plot:

  • A graph of ln k against 1/T can be plotted, and then used to calculate Ea
    • This gives a line which follows the form y = mx + c

Arrhenius sketch of ln k against 1_T, downloadable AS & A Level Chemistry revision notes

The graph of ln k against 1/T is a straight line with gradient -Ea/R

  • From the graph, the equation in the form of y = mx + c is as follows:

Y = mx + c from Arrhenius graph, downloadable AS & A Level Chemistry revision notes

Worked Example

  1. Complete the following table
  2. Plot a graph of ln k against 1/T
  3. Use this to calculate the activation energy, Ea, and the Arrhenius constant, A, of the reaction.

Calculate the activation energy from the Arrhenius plot - WE, downloadable AS & A Level Chemistry revision notes

Answers

Answer 1:

Using Arrhenius plot to calculate Ea - calculation answer complete table (WE), downloadable AS & A Level Chemistry revision notes

Answer 2:

using Arrhenius plot to calculate Ea - plotted graph (WE), downloadable AS & A Level Chemistry revision notes

Answer 3: WE Arrhenius plot calculate Ea 1, downloadable AS & A Level Chemistry revision notes

WE Arrhenius plot calculate Ea 2, downloadable AS & A Level Chemistry revision notes

WE Arrhenius plot - calculate A (part 1), downloadable AS & A Level Chemistry revision notes

WE Arrhenius plot - calculate A (part 2), downloadable AS & A Level Chemistry revision notes

Exam Tip

You are not required to learn these equations.

However, you do need to be able to rearrange them, and knowing them is helpful in understanding the effects of temperature on the rate constant.

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