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5.2.4Solids, Liquids and Gases

Specific Heat Capacity

5 min read 5 parts Lesson 14 of 23 Unit quiz

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Section 1 of 5Defining Specific Heat Capacity

5.2.4 Specific Heat Capacity

Specific heat capacity describes how much energy a material needs to warm up.

Specific heat capacity
  • The energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Units
  • It is measured in joules per kilogram per degree Celsius, written J/(kg °C).
Water
  • Water has a high specific heat capacity of about 4200 J/(kg °C), so it takes a lot of energy to heat.
Larger value
  • A substance with a larger specific heat capacity stores more thermal energy for the same temperature rise.

Section 2 of 5Factors Affecting Energy Needed

The energy needed to heat an object depends on three quantities.

Factors Affecting Energy Needed
Mass
  • A larger mass needs more energy to be heated through the same temperature rise.
Temperature change
  • A bigger rise in temperature needs proportionally more energy.
Substance
  • Different substances have different values of c, so the same energy gives different temperature rises.
Practical uses
  • Water is used in heating and cooling systems because of its high specific heat capacity.

Section 3 of 5Using ΔQ = m × c × ΔT

Keep each quantity in its correct unit before multiplying.

1
Write the equation ΔQ = m × c × ΔT, with ΔQ in joules, m in kilograms and ΔT in degrees Celsius.
2
Identify the mass, the specific heat capacity of the substance and the temperature change.
3
Multiply the mass, the specific heat capacity and the temperature change to find the energy in joules.
4
Use the temperature difference for ΔT, which is the same size in kelvin and in degrees Celsius.

Section 4 of 5Worked Example

Question

  • Calculate the energy needed to heat 0.50 kg of water from 20 °C to 30 °C.
  • The specific heat capacity of water is 4200 J/(kg °C).

  1. ΔT = 30 °C − 20 °C = 10 °C.
  2. ΔQ = m × c × ΔT = 0.50 kg × 4200 J/(kg °C) × 10 °C.
  3. ΔQ = 21 000 J.

Answer The energy needed is 21 000 J, or 2.1 × 10⁴ J.

Section 5 of 5Exam Checklist & Tips

5.2.4 – 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 The energy stored by the particles of a substance, linked to its temperature.
  • Temperature change The difference between the final and initial temperatures.
  • Joule The SI unit of energy.
  • Degree Celsius A unit of temperature, with a change of 1 °C equal to a change of 1 K.

Common Mistakes

  • Using the final temperature instead of the temperature change in the equation.
  • Forgetting to convert grams into kilograms before multiplying.
  • Saying a material with a high specific heat capacity heats up quickly; it heats up more slowly.
  • Confusing specific heat capacity, which is for 1 kg, with the heat capacity of a whole object.
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