Calculating rates of reactions Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher

What does the mean rate of a reaction describe?

How fast a reactant is used up or a product is formed, on average over a time interval.

How do you calculate the mean rate of a reaction?

Divide the quantity of reactant used or product formed by the time taken.

What rate units correspond to mass, volume and amount measured in grams, cubic centimetres and moles?

• Mass: $\mathrm{g/s}$
• Volume: $\mathrm{cm^3/s}$
• Amount (Higher Tier): $\mathrm{mol/s}$

What does a curved quantity–time graph show about the rate of reaction?

The rate is changing during the reaction.

What is a tangent to a curve at a chosen point?

A straight line that just touches the curve at that point and follows its direction there.

How do you calculate the rate of reaction at a specific time from a curved quantity–time graph?

Draw a tangent at the chosen time. Use two well-chosen points on the tangent to calculate its gradient: $\text{rate} = \frac{\text{change in quantity}}{\text{change in time}}$