Question 1: Define a heating curve and explain what information it provides about a substance.

Answer: A heating curve is a graph that shows how the temperature of a substance changes as it is heated, indicating phase changes and the energy required at each stage.

Question 2: Describe what occurs at the flat sections of a heating curve during phase change.

Answer: At flat sections, the temperature remains constant while the substance undergoes a phase change, such as melting or boiling, where energy is used to change the state rather than increase temperature.

Question 1: A 200 g block of ice at -10°C is heated until it becomes water at 80°C. How much energy (in joules) is required to heat the ice to 0°C, melt it, and then heat the water to 80°C? (Specific heat capacity of ice = 2100 J/kg°C, water = 4200 J/kg°C, heat of fusion of ice = 334,000 J/kg).

Answer: Energy = (mass x specific heat x temperature change) + (mass x heat of fusion) + (mass x specific heat of water x temperature change) = 0.2 kg x 2100 J/kg°C x 10°C + 0.2 kg x 334,000 J/kg + 0.2 kg x 4200 J/kg°C x 80°C = 4200 J + 66,800 J + 67,200 J = 138,200 J.

Question 1: Outline the key variables you would control in an experiment to produce a heating curve for water.

Answer: Control variables include the mass of water, initial temperature, and the rate of heating; measurement should be done using a thermometer and a controlled heat source.

Question 2: List two safety precautions to observe when heating substances in a laboratory setting.

Answer: Use heat-resistant gloves and goggles; ensure the heat source is stable and away from flammable materials.

Question 1: A substance's temperature was recorded as it was heated from 20°C to 100°C. During the heating process, the temperature remained constant at 50°C for 10 minutes. Explain what this indicates about the substance during this period.

Answer: The constant temperature at 50°C indicates the substance is undergoing a phase change, such as melting or boiling, where energy is used to change its state rather than increase temperature.

Question 1: Explain in detail how a heating curve can be used to determine the melting point and boiling point of a substance. Include the significance of the flat sections and how energy input relates to phase changes.

Answer: A heating curve displays temperature versus energy input. Flat sections indicate phase changes, where temperature remains constant despite energy being added. The melting point is identified at the flat section during melting, and the boiling point at the flat during boiling. The energy added during these flat sections corresponds to the heat of fusion or vaporisation, respectively, which are characteristic of the substance.

Question 1: Describe how understanding heating and cooling curves is important in the design of refrigeration systems or air conditioning units.

Answer: Understanding heating and cooling curves helps engineers determine the energy needed for phase changes, optimise heat exchange processes, and ensure efficient operation of refrigeration and air conditioning systems by controlling temperature and phase transitions effectively.