AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Changes of state and specific latent heat: mass, m, in kilograms, kg
Mass is the amount of matter in an object and is measured in kilograms, kg.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 7 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Mass is the amount of matter in an object and is measured in kilograms, kg. In specific latent heat calculations, m is the mass of the substance changing state, and it must be in kilograms so that the product mL gives energy in joules when L is in J/kg. One kilogram is 1000 grams, so 250 g is 0.25 kg. For example, to find the energy needed to boil 0.20 kg of water with L = 2.26 × 10⁶ J/kg, use E = mL = 0.20 × 2.26 × 10⁶ = 4.52 × 10⁵ J. Mass is not the same as weight; weight is a force in newtons, while mass in kg is constant anywhere. Always convert grams to kilograms before substituting into E = mL.
What earns the marks
- States that m represents mass and that its SI unit is the kilogram, kg.
- Converts masses from grams to kilograms by dividing by 1000.
- Uses m = E ÷ L correctly when rearranging the latent heat equation.
- Substitutes mass in kg into E = mL so that the energy answer is in joules.
- Distinguishes mass in kg from weight in N when interpreting a question.
- Checks that a calculated mass is given in kg with a sensible magnitude.
Common mistakes and how to put them right
Using grams directly in E = mL.
Put it right: Convert grams to kilograms by dividing by 1000.
Confusing mass with weight and giving the answer in newtons.
Put it right: Mass is in kg and weight is a force in N.
Rearranging E = mL incorrectly to m = L ÷ E.
Put it right: Divide energy by specific latent heat, m = E ÷ L.
Exam tips
- Write down the mass in kg before substituting into any equation.
- If the question gives grams, show the conversion step clearly.
- Check the unit of your final mass answer and include kg.
Try the lesson
The start of the Changes of state and specific latent heat: mass, m, in kilograms, kg lesson, made from checked teaching notes for this specification point.
Have a go first
In the equation E = m × L, what does the symbol m represent, and in which unit is it measured?
Listen
Mass is the amount of matter in an object and is measured in kilograms, kg. In specific latent heat calculations, m is the mass of the substance changing state, and it must be in kilograms so that the product mL gives energy in joules when L is in J/kg. One kilogram is 1000 grams, so 250 g is 0.25 kg. For example, to find the energy needed to boil 0.20 kg of water with L = 2.26 × 10⁶ J/kg, use E = mL = 0.20 × 2.26 × 10⁶ = 4.52 × 10⁵ J. Mass is not the same as weight; weight is a force in newtons, while mass in kg is constant anywhere. Always convert grams to kilograms before substituting into E = mL. A strong answer earns marks for these points. States that m represents mass and that its SI unit is the kilogram, kg. Converts masses from grams to kilograms by dividing by 1000. Uses m = E ÷ L correctly when rearranging the latent heat equation. Substitutes mass in kg into E = mL so that the energy answer is in joules. A common slip: Using grams directly in E = mL. Instead, convert grams to kilograms by dividing by 1000. Exam tip: Write down the mass in kg before substituting into any equation.
Key words
Say what each word means before you turn the card.
mass
Try answering aloud or in your head before turning the card.
weight
Try answering aloud or in your head before turning the card.
kilogram
Try answering aloud or in your head before turning the card.
m = E ÷ L
Try answering aloud or in your head before turning the card.
See every definition
- mass
- The amount of matter in an object, measured in kilograms, kg.
- weight
- A force in newtons, which is not the same as mass in kg.
- kilogram
- The SI unit of mass, where one kilogram is 1000 grams.
- m = E ÷ L
- The rearrangement used to calculate mass from energy and specific latent heat.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Changes of state and specific latent heat: mass, m, in kilograms, kg
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge