Measuring Speed of Reaction

In module 6.2, you will learn to

1. interpret data obtained from experiments concerned with speed of reaction.
2. suggest a suitable method for investigating the effect of a given variable on the speed of a reaction.

In module 6.1, we understand that the frequency of collision and the level of activation energy directly affect the speed of reaction. Also, we briefly discussed how do we measure the rate of reaction, by measuring either the rate of reactants consumed or the rate of products formed. If you still unsure, please click on this link on the new tab!

Now we will discuss in-depth how to measure the rate of reaction experimentally.

Ways to Measure Rate of Reaction Experimentally

1. Measure the decrease in mass of reactants per unit time
2. Measure the volume of gas products produced per unit time

(1) Measuring the Decrease in Mass of Reactants Per Unit Time

We can measure the rate of reaction by monitoring the mass lost during a reaction. The mass of all the substances actually remain the same before and after the reaction, because of the Conservation of Mass.

But, we can measure the decrease of mass in a reaction because some of the products escape out of our system. They are the gaseous products.

For example, if we have a reaction of magnesium and dilute hydrochloric acid in a conical flask, the mass of the conical flask will decrease over time.

This is because hydrogen gas is produced, and the hydrogen gas escape out of the conical flask, giving rise to the loss of mass.

We can measure the rate of decrease to determine the speed of reaction. Note that this is only suitable for reactions that involve gaseous products.

The faster the mass loss per unit time, the higher the speed of reaction. If the mass loss per unit time is high, this means that the reaction occurs very fast to produce the gaseous product which escape to the surroundings, causing a faster decrease in mass.

(2) Measuring the Volume of Gas Produced Per Unit Time