Topic 6.1: Rates of reaction

6.1.1 Define the term rate of reaction

The rate of a reaction is the increase in concentration of products (or the decrease in concentration of reactants) per unit time. It is measured in mol dm^-3 s^-1

6.1.2 Describe suitable experimental procedures for measuring rate of reaction

There are several suitable experimental procedures

• Change in volume of gas produced

Gas syringe or inverted beakers to collect gas produced

• Change in mass

If the reaction is giving off a gas, the corresponding decrease in mass can be measured by standing the reaction mixture directly on a balance.

• Change in transmission of light: colorimetry/spectrophotometry

As the concentration of coloured compound increase, it absorbs porportionally more light, so less is transmitted. A photocell generates an electric current according to the intensity of the light transmitted.

• Change in concentration measured using titration

Through the method of quenching, we could obtain freeze frames from the experiment. Thus showing all the points.

• Change in concentration measured using conductivity

Conductivity can be measured directly using a conductivity meter.

• "Clock reaction"

Simply measures the time taken to reach its final point. Thus the rate given is an average.


6.1.3 Analyse data from rate experiments

There will be a steady decreasing rate of temperature.

Assuming that the decrease of temperature is uniform, we could deduce the original temperature without heating process.

Thus, find the temperature change and calculate the for enthalpy change.