Question 1: Define the term 'evaporation'.

Answer: Evaporation is the process by which a liquid turns into a gas at temperatures below its boiling point.

Question 2: Explain the mechanism of melting in terms of particle movement.

Answer: Melting occurs when particles gain enough energy to overcome their fixed positions, allowing the solid to turn into a liquid.

Question 3: What is the main difference between boiling and evaporation?

Answer: Boiling occurs throughout the liquid at a specific temperature, producing bubbles, whereas evaporation only occurs at the surface at temperatures below boiling point.

Question 1: Calculate the energy required to convert 50 g 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: Q = mcΔT + mL

Question 1: Describe a safe method to heat a liquid to observe evaporation, including safety precautions.

Answer: Use a water bath or a heat-resistant container on a controlled heat source, wear safety goggles and heat-resistant gloves, and ensure proper ventilation.

Question 2: Identify the independent and dependent variables in an experiment to measure the boiling point of water.

Answer: Independent variable: temperature of the water; dependent variable: boiling point temperature.

Question 1: A sample of liquid is heated, and vapour is observed forming at the surface before boiling begins. Explain this process.

Answer: This process is evaporation, where particles at the surface gain enough energy to escape into the gas phase before the temperature reaches boiling point.

Question 2: During cooling, a gas condenses into a liquid. Describe the particle movement and energy change involved.

Answer: Particles lose energy, move closer together, and transition from a less ordered (gas) to a more ordered (liquid) state, releasing latent heat.

Question 1: Explain why water boils at a lower temperature at higher altitudes, and how this affects cooking times.

Answer: At higher altitudes, atmospheric pressure is lower, which lowers the boiling point of water. This means water boils at a temperature below 100°C, causing food to cook more slowly because the heat energy is less than at sea level.

Question 2: In the industry, how is the process of distillation used to separate components based on their boiling points? Describe the principle and a typical application.

Answer: Distillation separates mixtures by heating them to different boiling points so that components vaporise at different temperatures. The vapour is then cooled and condensed back into liquid. It is used in refining crude oil into fuels and in producing pure chemicals.