4.2.4Solids, Liquids and Gases: Part 1
Specific Heat Capacity
5 min read 5 parts Lesson 8 of 9 Unit quiz
Section 1 of 5The Idea
The Idea
Definition
- Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Equation
- Change in thermal energy ΔQ = m × c × Δθ, where m is the mass, c the specific heat capacity and Δθ the temperature change.
Units
- ΔQ is in joules, m in kilograms, c in J/kg °C and Δθ in degrees Celsius.
Meaning
- A large specific heat capacity means a lot of energy is needed to change the temperature of the material.
Section 2 of 5Substances Compared
Water
- Water has a high specific heat capacity of about 4200 J/kg °C, so it heats and cools slowly.
Metals
- Metals such as aluminium (about 900 J/kg °C) warm up with far less energy than water for the same mass.
Uses of water
- Water is used in central heating and cooling systems because it carries a large amount of energy.
Climate
- Large bodies of water warm up slowly, which keeps coastal areas cooler in summer and warmer in winter.
| Substance | c (J/kg °C) |
|---|---|
| Water | 4200 |
| Aluminium | 900 |
| Copper | 390 |
| Iron | 450 |
Section 3 of 5Calculation Routine
1
Write down the known values and convert the mass into kilograms.
2
Find the temperature change by subtracting the starting temperature from the final temperature.
3
Substitute into ΔQ = m × c × Δθ, or rearrange to make c, m or Δθ the subject.
4
Calculate carefully and give the answer in joules (or kilojoules if asked).
5
Check whether the answer is sensible, for example that a small mass needs little energy.
Section 4 of 5Worked Example
Question
- Calculate the energy needed to heat 2.0 kg of water from 20 °C to 70 °C.
- (Specific heat capacity of water = 4200 J/kg °C)
- Temperature change Δθ = 70 − 20 = 50 °C.
- ΔQ = m × c × Δθ.
- ΔQ = 2.0 × 4200 × 50.
- ΔQ = 420 000 J.
Answer 420 000 J (4.2 × 10⁵ J).
Section 5 of 5Exam Checklist & Tips
4.2.4 – Key Points for the Exam
- Specific heat capacity The energy needed to raise the temperature of 1 kg of a substance by 1 °C.
- Thermal energy Energy stored in the thermal store of a substance, linked to its temperature.
- Temperature change Final temperature minus initial temperature, written Δθ.
- Joule The unit of energy.
- Heat capacity The energy needed to raise the temperature of a whole object by 1 °C.
Common Mistakes
- Using grams instead of kilograms for the mass.
- Using the final temperature rather than the temperature change.
- Mixing up specific heat capacity with specific latent heat; the first changes temperature.
- Giving the unit of c as J/kg without the °C.