Graphs are used to show how the rate of reaction changes over time. They help us compare how fast reactions happen and when they are complete.

What does a rate of reaction graph show?

• The amount of product formed or reactant used up on the y-axis
• Time on the x-axis
• The steeper the line, the faster the reaction
• When the line levels off, the reaction has finished

Types of rate graphs

1. Product formed over time

• Starts steep (reaction is fast)
• Curve gets less steep (reactants being used up)
• Line flattens (reaction is complete)

2. Reactant used over time

• Starts steep (reactant used quickly)
• Slows down over time
• Levels off when no reactants remain

Comparing reaction rates

You can compare:

• Steepness of the curve (steeper = faster)
• Final volume or mass (more product = more reactants reacted)
• Time taken to reach completion

💡 A catalysed reaction or one at higher temperature will have a steeper curve that levels off sooner

Calculating rate from a graph

• To calculate rate at a specific point, draw a tangent to the curve
• Measure the gradient of the tangent:

Rate = change in y ÷ change in x

Units might be:

• cm³/s (for gas produced)
• g/s (for mass lost)

Key features to look for