Question 1: Define a heating curve and explain what it represents in terms of particle behavior during phase changes.

Answer: A heating curve shows how the temperature of a substance changes as it is heated, illustrating phase changes where temperature remains constant while particles gain or lose energy during transitions between solid, liquid, and gas.

Question 2: Describe what happens to the particles in a substance during the plateau sections of a heating or cooling curve.

Answer: During plateau sections, particles are undergoing a phase change (melting, vaporizing, condensing, or freezing), where energy is used to change the state without changing temperature, resulting in particle rearrangement.

Question 3: Explain why temperature remains constant during a phase change.

Answer: Temperature remains constant during a phase change because the energy supplied or removed is used to break or form intermolecular bonds, not to increase the kinetic energy of particles.

Question 1: A sample of sulfur is heated from 20°C to 120°C. The specific heat capacity of sulfur is 0.71 J/g°C. Calculate the amount of heat energy required to heat a 50g sample. Use the formula: Q = mcΔT.

Answer: Q = 50 g × 0.71 J/g°C × (120°C - 20°C) = 50 × 0.71 × 100 = 3550 Joules.

Question 2: A metal block cools from 150°C to 30°C over 10 minutes. Its mass is 200g, and its specific heat capacity is 0.9 J/g°C. Calculate the total heat lost during cooling.

Answer: Q = 200 g × 0.9 J/g°C × (150°C - 30°C) = 200 × 0.9 × 120 = 21,600 Joules.

Question 1: Describe a simple experimental setup to observe the cooling curve of water. What variables would you control, and what safety precautions should be taken?

Answer: Set up a container of water with a thermometer, and record temperature at regular intervals as it cools in a controlled environment. Control variables include initial temperature and environment temperature. Safety precautions involve handling hot water carefully to avoid burns and ensuring the thermometer is used safely.

Question 1: A forensic investigator finds a metal fragment that cooled from 300°C to room temperature (22°C) over 2 hours. The specific heat capacity of the metal is 0.5 J/g°C, and the mass is 100g. What is the total heat energy lost? How might this information help determine the time since the metal was heated?

Answer: Q = 100 g × 0.5 J/g°C × (300°C - 22°C) = 100 × 0.5 × 278 = 13,900 Joules. This energy loss can help estimate how long ago the metal was heated based on cooling rates, assisting in forensic timing.

Question 1: Describe the significance of the plateau sections in a heating or cooling curve in forensic investigations involving metal objects.

Answer: Plateau sections indicate phase changes, such as melting or solidification, which can reveal the temperature at which a metal changes state. This information helps determine if a metal has been recently heated or cooled, aiding forensic timelines.

Question 2: A 150g sample of aluminum is heated from 25°C to 200°C. The specific heat capacity of aluminum is 0.9 J/g°C. Calculate the energy required. Discuss how this energy relates to phase changes if the aluminum melts at 660°C.

Answer: Q = 150 g × 0.9 J/g°C × (200°C - 25°C) = 150 × 0.9 × 175 = 23,625 Joules. Since aluminum melts at 660°C, no phase change occurs at 200°C; energy relates solely to heating the solid.

Question 3: Explain how forensic scientists might use cooling curves to determine the time since a metal object was heated during a crime scene investigation.

Answer: By measuring the current temperature of the metal and understanding its cooling rate (derived from laboratory data), forensic scientists can estimate how long it has been cooling since it was heated. This helps establish timelines and link suspects or events to the scene.