Heat and Thermodynamics: JAMB Physics Notes

Specific heat capacity, latent heat, and the gas laws that describe how gases respond to changes in pressure, volume, and temperature.

Heating without changing state

The heat energy needed to change a substance's temperature is $Q = m c Δ T$ , where $c$ is the specific heat capacity and $Δ T$ is the temperature change.

Example 1: Find the heat needed to raise the temperature of 2 kg of water from 20°C to 80°C (specific heat capacity of water = 4200 J/kg°C).

$Q = m c Δ T = 2 \times 4200 \times 60 = 504, 000 J = 504 k J$ .

Latent heat and changes of state

During melting, freezing, boiling, or condensing, temperature stays constant while heat is absorbed or released to break or form bonds between particles: $Q = m L$ , where $L$ is the specific latent heat.

Example 2: Find the heat needed to melt 0.5 kg of ice at 0°C (specific latent heat of fusion of ice = 334,000 J/kg).

$Q = m L = 0.5 \times 334, 000 = 167, 000 J = 167 k J$ .

The gas laws

Boyle's law (constant temperature): $P_{1} V_{1} = P_{2} V_{2}$ . Charles' law (constant pressure): $\frac{V _{1}}{T _{1}} = \frac{V _{2}}{T _{2}}$ , with temperature always in kelvin ( $K = ° C + 273$ ). These combine into $\frac{P _{1} V _{1}}{T _{1}} = \frac{P _{2} V _{2}}{T _{2}}$ .

Example 3: A gas occupies 2 L at a pressure of 100 kPa. Find its new volume if the pressure increases to 200 kPa at constant temperature.

$P_{1} V_{1} = P_{2} V_{2}$ : $100 \times 2 = 200 \times V_{2}$ , so $V_{2} = 1 L$ .

Thermal expansion

Most solids, liquids, and gases expand when heated because increased particle vibration pushes neighbouring particles further apart on average. This is why bridges have expansion gaps and why a thermometer's liquid rises as it warms.

Heat and Thermodynamics

Heating without changing state

Latent heat and changes of state

The gas laws

Thermal expansion

Key terms

Practise Heat and Thermodynamics questions

Related topics

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