Question 1: Define internal energy in the context of the particle model of matter.

Answer: Internal energy is the total kinetic and potential energy stored within the particles of a substance, related to their random motion and interactions.

Question 2: Explain how the internal energy of a substance changes when it is heated at a constant pressure.

Answer: The internal energy increases as heat energy is transferred to the particles, causing them to move faster and potentially changing the state of the substance.

Question 1: A kilogram of water absorbs 420 kJ of heat energy. If the specific heat capacity of water is 4200 J/(kg·°C), calculate the increase in temperature of the water.

Answer: 100°C

Question 2: A block of aluminium with mass 2 kg is heated, resulting in an increase in internal energy of 36 kJ. If the specific heat capacity of aluminium is 900 J/(kg·°C), what is the temperature change?

Answer: 20°C

Question 1: Describe a simple experiment to investigate how the internal energy of a gas changes with temperature. Include the key variables and safety precautions.

Answer: A possible experiment involves heating a fixed mass of gas in a sealed container and measuring its temperature and pressure. Variables include heat input (independent), temperature and pressure (dependent). Safety precautions include using a heat-resistant container, avoiding over-pressurisation, and handling hot equipment with care.

Question 1: A sample of sulphur is heated from 25°C to 100°C at constant pressure. The internal energy increases by 15 kJ. Explain what this data suggests about the particle activity within the sample.

Answer: The increase in internal energy indicates that the particles are moving faster as temperature rises, increasing their kinetic energy. The energy may also be used to overcome intermolecular forces if a phase change occurs.

Question 2: A container holds 0.5 kg of water, which is heated from 20°C to 80°C, absorbing 150 kJ of heat. Determine if the internal energy change aligns with the specific heat capacity of water (4200 J/(kg·°C)) and justify your reasoning.

Answer: Yes, because ΔU = mcΔT = 0.5 kg × 4200 J/(kg·°C) × 60°C = 126,000 J or 126 kJ, which is close to the 150 kJ absorbed, indicating most of the heat increased the internal energy.

Question 1: Explain how understanding the internal energy of steam is important in designing efficient steam turbines used in electricity generation.

Answer: Knowing the internal energy of steam helps optimise the energy transfer process, ensuring maximum efficiency in turbines by controlling temperature and pressure conditions to harness the most energy from the steam.

Question 2: Discuss how the concept of internal energy is applied in the refrigeration cycle to cool substances or environments.

Answer: In refrigeration, internal energy decreases as the refrigerant absorbs heat from the environment. The cycle involves phase changes and energy transfers that enable cooling, relying on understanding how internal energy varies during compression, expansion, and phase change processes.