Topic Two (1.2): Rate Equations, Rate Constant and the Order of a Reaction

Introduction Icon.png Introduction

In most instances when we double the concentration of a reactant the rate of the reaction also doubles. If we plot a graph of concentration vs rate, we would expect a straight line with a positive gradient and can say that the rate is directly proportional to the concentration.

In real life this is not always the case. Sometimes if we double the concentration the rate increases by a factor of four. In this section consider the graphs drawn from experimental data and work out the order of the reaction. From this we can calculate the rate constant.

Read Icon.png Reading

Edexcel AS/A Level Chemistry Student Book 2 pages 7 to 14

Make Notes Icon.png Tasks

Complete the following:

WATCH - Kinetics: Chemistry’s Demolition Derby (YouTube) Links to an external site.

  • Read pages 7 to 14 and take notes. Take care to carefully review worked examples.
  • Complete the ‘checkpoint’ questions.
  • Note subject vocabulary (revision cards are useful).
  • Draw examples of reaction graphs onto revision cards.

WATCH - The Rate Law: Bozeman Science (YouTube) Links to an external site.

WATCH - The Rate Constant: Bozeman Science (YouTube) Links to an external site.

Experiments Icon.png Practical Knowledge

WATCH - Reaction of Calcium Carbonate with Hydrochloric Acid (YouTube) Links to an external site.

Download REVIEW & COMPLETE - Practical Exercise 4.1: The Kinetics of the Reaction between Calcium Carbonate and Hydrochloric Acid

  • For further information review the following student sheet and video:

Download REVIEW - Practical Exercise 4.1 Further Information (Nuffield Information)

WATCH - Calcium Carbonate Rate of Reaction (YouTube) Links to an external site.

  • When you have completed the virtual practical, check your answers:

Download CHECK - Practical 4.1 Answers

WATCH - Reaction Between Iodine and Propanone in Acid Solution (YouTube) Links to an external site.

Download REVIEW & COMPLETE - Practical Exercise 4.2: The Kinetics of the Reaction between Iodine and Propanone in Acid Solution

  • When you have completed the virtual practical, check your answers:

Download CHECK - Practical 4.2 Answers

Download REVIEW - Kc Calculation (PowerPoint)

Top Tip Icon.png Top Tips

Make sure that you understand the following key points:

  • UNITS! Work them out with care.
  • All reactant species before the rate determining step will have an effect on the rate of the reaction and will appear in the rate equation.

Glossary Icon.png Key Terms

Add the following key terms with definitions to your glossary.

  • Rate equation
  • Order
  • Overall order
  • Rate determining step
  • Half life
  • Instantaneous reaction rate