AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Change in thermal energy, ∆E, in joules, J
Full specification wording
Temperature changes in a system and specific heat capacity: change in thermal energy, ∆E, in joules, J
When a material is heated or cooled, its internal energy store changes.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 6 of 10
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When a material is heated or cooled, its internal energy store changes. The change in thermal energy, ∆E, is the energy transferred to or from the material, measured in joules, J. The symbol ∆ means 'change in', so ∆E is the difference between the final and initial thermal energy, not the total energy the object contains. For a temperature rise, ∆E is positive; for a fall, ∆E is negative. You calculate it using ∆E = mc∆θ, where m is mass in kg, c is specific heat capacity in J/kg°C and ∆θ is the temperature change in °C. For example, heating 2 kg of water (c = 4200 J/kg°C) by 10 °C transfers ∆E = 2 × 4200 × 10 = 84 000 J. In calculations, always identify the temperature change first, then substitute values with units.
What earns the marks
- States that ∆E is the change in thermal energy of a system, measured in joules, J.
- Explains that ∆ means 'change in', so ∆E is the difference between final and initial thermal energy.
- Uses the equation ∆E = mc∆θ, identifying m as mass in kg, c as specific heat capacity and ∆θ as temperature change.
- Calculates ∆E correctly from given values, including converting grams to kilograms and using the correct temperature change.
- Interprets a negative value of ∆E as energy transferred away from the material, causing cooling.
- Recognises that ∆E depends on mass, material and temperature change, not on the starting temperature alone.
Common mistakes and how to put them right
Using the final temperature instead of the temperature change.
Put it right by calculating ∆θ = final temperature − initial temperature before substituting.
Forgetting to convert grams to kilograms.
Put it right by dividing the mass in grams by 1000 to obtain kilograms.
Writing the unit as J/°C or J/kg.
Put it right by remembering that energy is measured in joules, J, while J/kg°C is the unit of specific heat capacity.
Exam tips
- Write the equation ∆E = mc∆θ before substituting numbers so the examiner can follow your method.
- Check that mass is in kg and temperature change is in °C before calculating, and include the unit J with your answer.
- If a temperature falls, expect a negative ∆E and comment that thermal energy is transferred from the material to the surroundings.
Try the lesson
The start of the Temperature changes in a system and specific heat capacity: change in thermal energy, ∆E, in joules, J lesson, made from checked teaching notes for this specification point.
Have a go first
A heater transfers 5000 joules of energy to a block of metal, causing it to warm up. Which symbol represents this change in thermal energy, and what is its standard unit?
Listen
When a material is heated or cooled, its internal energy store changes. The change in thermal energy, ∆E, is the energy transferred to or from the material, measured in joules, J. The symbol ∆ means 'change in', so ∆E is the difference between the final and initial thermal energy, not the total energy the object contains. For a temperature rise, ∆E is positive; for a fall, ∆E is negative. You calculate it using ∆E = mc∆θ, where m is mass in kg, c is specific heat capacity in J/kg°C and ∆θ is the temperature change in °C. For example, heating 2 kg of water (c = 4200 J/kg°C) by 10 °C transfers ∆E = 2 × 4200 × 10 = 84 000 J. In calculations, always identify the temperature change first, then substitute values with units. A strong answer earns marks for these points. States that ∆E is the change in thermal energy of a system, measured in joules, J. Explains that ∆ means 'change in', so ∆E is the difference between final and initial thermal energy. Uses the equation ∆E = mc∆θ, identifying m as mass in kg, c as specific heat capacity and ∆θ as temperature change. Calculates ∆E correctly from given values, including converting grams to kilograms and using the correct temperature change. A common slip: Using the final temperature instead of the temperature change. Instead, calculating ∆θ = final temperature − initial temperature before substituting. Exam tip: Write the equation ∆E = mc∆θ before substituting numbers so the examiner can follow your method.
Key words
Say what each word means before you turn the card.
Change in thermal energy
Try answering aloud or in your head before turning the card.
Specific heat capacity
Try answering aloud or in your head before turning the card.
Temperature change
Try answering aloud or in your head before turning the card.
See every definition
- Change in thermal energy
- The energy transferred to or from a material when it is heated or cooled, measured in joules, J.
- Specific heat capacity
- The quantity c in the equation ∆E = mc∆θ, measured in J/kg°C.
- Temperature change
- The difference between the final and initial temperature, written ∆θ and measured in °C.
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