MYP 10
 
 


Unit 10.6.1: Introduction to rates of reaction

Objectives

  • To appreciate that chemical reactions proceed at different rates
  • To know that reactions require a 'push' to get started, the activation energy
  • To understand that to follow a chemical reaction there must be something to measure
  • To understand that the reciprocal of time taken can be used as a measure of average rate

Introduction

Discussion of the meaning of 'Rate' as applied to chemical reactions. Analogy with rate of travel leading to the idea that the average rate is proportional to the reciprocal of the time taken. Stress the danger of using minutes and seconds.

Point out that we must be able to measure a property of one of the components of the reaction that changes in some way (pH, gas volume, colour, mass due to gas loss, conductivity etc).

Another condition is that the rate must not be too slow (oxidation of sugar) nor too fast (hydrogen and oxygen).

During the discussion there could be a variety of experiments that proceed at different rates:

  • The reaction between sulfuric acid and zinc (catalysed by copper 2+ ions)
  • The decomposition of hydrogen peroxide (catalysed by manganese(IV) oxide)
  • The reaction between 2M HCl and 0.04 mol dm-3 sodium thiosulfate solution
  • The reaction between oxygen and hydrogen (plastic bottle)

Student follow up

Worksheet on the rate of chemical reactions.

Assessment

None

Teaching notes

If the oxygen and hydrogen is prepared during the class using gas generator apparatus (conical flask, thistle funnel, delivery tube) then it can serve as a demonstration of gas collection to measure rate and also to prepare the plastic bottle explosion.

Resources

The rates of chemical reactions


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