What a rate of reaction is, how to measure one, and how to work out a mean rate with the right unit.
What you will learn
- Calculate a mean rate from a mass or a volume and a time
- Give the unit of a rate
- Choose a way to follow a reaction
How fast is a reaction?
The rate of a reaction tells you how quickly reactants turn into products.
A rusting bike takes months; a firework takes a fraction of a second.
You can measure how much of a reactant is used up, or how much of a product is made, over a period of time:
mean rate of reaction = quantity of reactant used ÷ time taken
mean rate of reaction = quantity of product formed ÷ time taken
Recall both: chemistry papers give no equation sheet. The quantity can be a mass in g, a volume of gas in cm³ or (Higher) an amount in mol, so the rate is in g/s, cm³/s or mol/s.
- A flask loses 1.50 g of carbon dioxide in 120 s
- mean rate = 1.50 ÷ 120 = 0.0125 g/s
- A gas syringe collects 45 cm³ of hydrogen in 30 s
- mean rate = 45 ÷ 30 = 1.5 cm³/s
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- How fast is a reaction?
- Three ways to follow a reaction
- Higher: rate in mol/s
- Try it: Your first rate
8 practice questions, marked as you go; about 20 minutes in all.
Key terms
Loss of mass, Volume of gas, Precipitate
In this unit: Rates of reaction and equilibrium
Measuring and graphing rates, collision theory and the factors that change a rate, the rates required practical, reversible reactions and how conditions move an equilibrium.