This guide covers the fundamental concepts of heat, temperature, changes of state, and how heat is transferred. Understanding the difference between heat and temperature is crucial, as is mastering the key formula Q = mcθ.

1. Temperature and Heat

Short Notes & Key Concepts

• Temperature: A measure of the hotness or coldness of an object. Scientifically, it's a measure of the average kinetic energy of the particles in an object.

  • Measured with a thermometer.

  • Units:

    • Celsius (°C): Based on the freezing (0°C) and boiling (100°C) points of water.

    • Kelvin (K): The absolute temperature scale. The SI unit for temperature. 0 K is absolute zero, the coldest possible temperature.

• Heat: The transfer of thermal energy from a hotter object to a colder object due to a temperature difference.

  • Heat is a form of energy.

  • Unit: Joules (J).

  • Heat always flows from a region of high temperature to a region of low temperature.

• Converting Between Celsius and Kelvin:

  • To convert Celsius to Kelvin: K = °C + 273

  • To convert Kelvin to Celsius: °C = K - 273

  • Tip: A change in temperature is the same in both scales (e.g., a change of 10°C is also a change of 10 K).

2. Heat Capacity & Specific Heat Capacity

• Heat Capacity (C): The amount of heat energy required to raise the temperature of an entire object by 1°C or 1 K.

• Specific Heat Capacity (c): The amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C or 1 K.

  • This is a property of the material, not the object.

  • Water has a very high specific heat capacity (4200 J kg⁻¹ °C⁻¹), meaning it takes a lot of energy to heat it up, but it also stores a lot of heat.

• The Key Formula: Q = mcθ

  • Q = Heat energy transferred (Joules, J)

  • m = mass (kilograms, kg)

  • c = specific heat capacity (J kg⁻¹ °C⁻¹ or J kg⁻¹ K⁻¹)

  • θ = change in temperature (°C or K)

3. Changes of State & Latent Heat

• Change of State: When a substance changes from solid, liquid, or gas. This happens at a constant temperature (melting point or boiling point).

• Latent Heat: The energy absorbed or released during a change of state at a constant temperature. This energy is used to break or form bonds between particles, not to increase their kinetic energy.

  • Latent Heat of Fusion: Heat absorbed to change a solid to a liquid at the melting point.

  • Latent Heat of Vaporization: Heat absorbed to change a liquid to a gas at the boiling point.

• Key Point: A burn from steam at 100°C is more severe than a burn from water at 100°C. This is because the steam releases a large amount of latent heat of vaporization when it condenses on the skin, in addition to the heat from the hot water.

4. Heat Transfer

Heat can move from one place to another in three ways.

• Conductors vs. Insulators:

  • Conductors (e.g., metals) transfer heat easily.

  • Insulators (e.g., wood, plastic, air) do not transfer heat well.

• Radiation Surfaces:

  • Dull, black surfaces are good absorbers and good emitters of radiation.

  • Shiny, silver/white surfaces are poor absorbers and poor emitters (they are good reflectors). This is why thermos flasks have shiny inner walls.

Exam Tips & Tricks

1. Don't Confuse Heat & Temperature: Temperature is a measure of the average kinetic energy of particles; Heat is the energy transferred due to a temperature difference.

2. Master Q = mcθ: This formula is almost always tested. Remember to use mass in kg. Practice rearranging it to find mass, specific heat capacity, or temperature change.

3. Latent Heat is "Hidden Heat": Remember that during melting or boiling, the temperature does not change. The heat energy supplied is "latent" or hidden, as it's used to change the state.

4. Know the 3 Transfer Methods: Be able to define conduction, convection, and radiation and give a clear example for each. Questions about everyday applications (thermos flask, cooking pots with black bottoms, sea breezes) are very common.

Think About Surfaces: For radiation questions, always link the colour and texture of the surface to its properties (dull/black = good absorber/emitter; shiny/white = poor absorber/emitter/good reflector).