Question 1: Define latent heat in the context of phase changes in matter.

Answer: Latent heat is the amount of energy required to change the state of a substance without changing its temperature.

Question 2: Explain why the temperature of a substance remains constant during melting or boiling, despite energy being added.

Answer: Because the energy supplied is used to break the intermolecular bonds, not to increase temperature.

Question 1: Calculate the energy required to melt 5 kg of ice at 0°C. (Specific latent heat of fusion of ice = 334 kJ/kg).

Answer: E = m × L E = 5 kg × 334 kJ/kg = 1670 kJ

Question 2: A litre of water (density = 1 kg/L) is heated from 20°C to 100°C. How much energy is required to convert this water to steam at 100°C? (Specific latent heat of vapourisation of water = 2256 kJ/kg).

Answer: Mass = 1 kg Energy to heat water = m × c × ΔT = 1 kg × 4.18 kJ/kg°C × (100 - 20)°C = 334.4 kJ Energy to vapourise = m × L = 1 kg × 2256 kJ/kg = 2256 kJ Total energy = 334.4 kJ + 2256 kJ = 2590.4 kJ

Question 1: Describe a simple experimental method to measure the latent heat of vaporisation of water. Include the key variables you would control and safety precautions.

Answer: Heat a known mass of water in a calorimeter until it boils, measure the energy supplied using a power supply and stopwatch, ensuring the water is contained safely in a heat-resistant vessel with a lid to minimise heat loss. Control variables include the mass of water, temperature, and heat source power. Safety precautions involve handling hot equipment with tongs, wearing safety goggles, and ensuring good ventilation.

Question 1: A 2 kg block of ice at -10°C is placed in 10 litres of water at 20°C in an insulated container. Describe the energy transfer process during melting and warming, and estimate the total energy needed to bring the system to equilibrium at 0°C.

Answer: The ice absorbs energy to warm from -10°C to 0°C (Q = m × c × ΔT), then latent heat is required to melt it. The water releases heat to cool from 20°C to 0°C. To estimate total energy: 1) Heat to warm ice: 2 kg × 2.1 kJ/kg°C × 10°C = 42 kJ; 2) Energy to melt ice: 2 kg × 334 kJ/kg = 668 kJ; 3) Heat to cool water: 10 kg × 4.18 kJ/kg°C × 20°C = 836 kJ. Total energy absorbed = 42 + 668 + 836 = 1546 kJ.

Question 1: Explain how latent heat is used in the process of refrigeration and air conditioning systems.

Answer: Latent heat is used to absorb heat from the surroundings during the evaporation of a refrigerant, cooling the environment; during condensation, heat is released. This cycle maintains a lower temperature in the cooled space.

Question 2: Identify one advantage and one disadvantage of using latent heat in thermal energy storage systems.

Answer: Advantage: Efficient storage of thermal energy for later use. Disadvantage: Limited to specific phase change materials and requires careful control of temperature to ensure phase change occurs correctly.