IB Chemistry: Rates of Reaction

IB Chemistry: Rates of Reaction

Rates of Reaction

1. Define the term rate of reaction.

This is essentially a reaction:

Reactants →Product

As a reaction occurs, the “concentration” of a reactant decreases as it forms the product, so the concentration of the products increases.

So we can define ‘rate of reaction’ as either:

• Decrease in concentration of the reactants per unit time.

OR

• Increase in concentration of the products per unit time.

2. Describe suitable experimental procedures for measuring rates of reactions.

We can calculate the change in concentration through a variety of methods:

• Mass Change
• Volume Changes
• Change in pH for reactions including acids and bases.
• Colorimeter for color change.

Use these devices to measure the volume produced, and then divided by the amount of time taken for the reaction to occur to get the rate of reaction

3. Analyse data from rate experiments

The graph below shows the rate of reaction of a substance over time.

To find the rate of reaction at a certain time, you simply have to find the gradient, which is the change in volume of gas produced divided by the time.

I usually use the “tangent method”, where you draw a tangent line which touches the specific time in which to calculate the rate of reaction.

The steeper the line, the faster the rate of reaction. This is because if the reaction graph is steeper, the gradient will have a higher value, and hence the rate of reaction will commence at a faster rate.