Question 1: Define a heating curve and describe what it represents in the context of a substance changing state.

Answer: A heating curve shows how the temperature of a substance changes as it is heated, illustrating phase changes such as melting and boiling by plateaus where temperature remains constant.

Question 2: Explain why the temperature remains constant during a phase change on a heating or cooling curve.

Answer: The temperature remains constant during a phase change because the energy supplied or removed is used to break or form bonds between particles, not to change the temperature.

Question 3: What is the significance of the flat sections (plateaus) on a heating/cooling curve?

Answer: Flat sections indicate phase changes where energy is used for melting or boiling (or condensation and freezing), during which temperature remains unchanged.

Question 1: A 500 g block of ice at -10°C is heated until it becomes water at 30°C. The specific heat capacity of ice is 2.1 J/g°C, the melting point of ice is 0°C, and the specific heat capacity of water is 4.2 J/g°C. Calculate the total energy supplied in joules. (Use Q = mcΔT for heating and cooling, and Q = mL for melting, where L = 334 J/g).

Answer: Q_total = (500 g)(2.1 J/g°C)(10°C) + (500 g)(334 J/g) + (500 g)(4.2 J/g°C)(30°C) = 10500 J + 167000 J + 63000 J = 240500 J.

Question 1: Describe an experiment to observe a heating curve of water. Include the variables to be controlled and measured, as well as safety precautions.

Answer: An experiment involves heating a known mass of water in a beaker using a controlled heat source, with a thermometer to record temperature changes over time. Variables to control include the amount of water, heating rate, and initial temperature. Measured variables are temperature and time. Safety precautions include handling hot equipment carefully, avoiding spills, and ensuring the heat source is stable and monitored.

Question 1: During a heating process, a substance shows a flat section at 100°C lasting for 10 minutes. Explain what is happening in this period and why the temperature does not increase.

Answer: The flat section at 100°C indicates the boiling point where the substance is converting from liquid to gas. The energy supplied is used for vaporisation, so temperature remains constant until all the liquid has turned to vapour.

Question 1: Describe the key features of a cooling curve for a substance that undergoes freezing. Include phase changes and temperature behaviour.

Answer: A cooling curve shows the temperature of a substance decreasing as it cools. Key features include a steep decline in temperature during cooling of the solid, a plateau during freezing as latent heat is released, and a continuous decrease until the substance reaches room temperature.

Question 1: How does knowledge of heating and cooling curves assist in the design of refrigeration systems?

Answer: It helps in selecting appropriate materials and refrigerants that efficiently undergo phase changes at desired temperatures, ensuring optimal cooling performance and energy efficiency.