Question 1: Define melting and explain what happens at the particle level during this process.

Answer: Melting is the change of a solid into a liquid when it gains enough energy; particles vibrate more vigorously until they overcome the forces holding them in fixed positions.

Question 2: Describe the difference between evaporation and boiling.

Answer: Evaporation is a slow process occurring at the surface of a liquid at temperatures below boiling point, while boiling is a rapid process where bubbles form throughout the liquid at its boiling point.

Question 3: What is the energy change involved in sublimation? Explain briefly.

Answer: Sublimation involves a direct change from solid to gas, requiring energy to overcome the forces holding the particles in the solid state, so it is an endothermic process.

Question 1: Calculate the energy required to convert 0.5 kg of ice at -10°C to water at 0°C. (Specific heat capacity of ice = 2.1 J/g°C, latent heat of fusion of ice = 334 J/g).

Answer: Energy = (mass × specific heat capacity × temperature change) + (mass × latent heat of fusion) = (500 g × 2.1 J/g°C × 10°C) + (500 g × 334 J/g) = 10,500 J + 167,000 J = 177,500 J

Question 1: Describe a simple experiment to demonstrate the boiling point of water. Include the variables you would control and safety precautions.

Answer: Heat a container of water using a Bunsen burner or electric heater, monitoring the temperature with a thermometer. Control the heat to maintain a steady temperature. Variables include temperature (independent), amount of water (controlled), and heating rate. Safety precautions include wearing safety goggles, handling hot equipment carefully, and avoiding water spillage near electrical sources.

Question 1: A sample of sulphur is heated and sublimates at 120°C under normal atmospheric pressure. Explain what is happening at the particle level during sublimation and why this process occurs at this temperature.

Answer: The sulphur particles gain enough energy to directly transition from the solid to gas phase, bypassing the liquid state, because the energy overcomes the forces holding the particles in a fixed position. The sublimation temperature is specific to sulphur under atmospheric pressure.

Question 1: Explain why water boils at 100°C at standard atmospheric pressure and describe how this temperature changes with altitude. Include the scientific principles involved.

Answer: Water boils at 100°C at standard atmospheric pressure because this is the temperature at which vapour pressure equals atmospheric pressure, allowing bubbles to form within the liquid. At higher altitudes, atmospheric pressure decreases, so the boiling point is lower because less energy is needed for vapour pressure to equal the external pressure.

Question 1: Describe how knowledge of latent heat is utilised in the design of refrigeration systems.

Answer: Refrigeration systems use the principle of latent heat by evaporating a refrigerant at low pressure to absorb heat from the surroundings, and then condensing it at high pressure to release heat elsewhere. This cycle relies on the latent heat during phase changes to transfer thermal energy efficiently.