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, resulting from their motion and interactions.

Question 2: Explain how an increase in temperature affects the internal energy of a sample of matter.

Answer: An increase in temperature increases the average kinetic energy of the particles, thereby increasing the internal energy of the substance.

Question 1: What are the main forms of energy stored within particles that contribute to internal energy?

Answer: The main forms are kinetic energy (from particle motion) and potential energy (from interactions between particles).

Question 2: Describe what happens to the internal energy when a solid is heated and melts into a liquid.

Answer: When heated, the particles gain more kinetic energy, increasing internal energy. During melting, energy is used to break the bonds between particles, increasing potential energy without raising temperature.

Question 1: A 2 kg aluminum block is heated from 20°C to 80°C. The specific heat capacity of aluminum is 900 J/(kg·°C). Calculate the change in internal energy of the block.

Answer: Change in internal energy = mass × specific heat capacity × temperature change = 2 kg × 900 J/(kg·°C) × (80°C - 20°C) = 2 kg × 900 J/(kg·°C) × 60°C = 108,000 J

Question 2: A forensic scientist finds a sulfur sample at a crime scene. The sulfur weighs 50 grams and was heated from 25°C to 150°C. The specific heat capacity of sulfur is 0.71 J/(g·°C). What is the internal energy increase?

Answer: Change in internal energy = mass × specific heat capacity × temperature change = 50 g × 0.71 J/(g·°C) × (150°C - 25°C) = 50 g × 0.71 J/(g·°C) × 125°C = 4,437.5 J

Question 1: Design a simple experiment to determine the specific heat capacity of a unknown metal object in a forensic laboratory setting. List the key variables and safety precautions.

Answer: Students should heat the metal to a known temperature, then submerge it in water of known mass and temperature. Measure temperature changes to calculate specific heat capacity. Variables include mass, temperature, and heat transfer; safety precautions involve handling hot objects with tongs and wearing safety goggles.

Question 2: In forensic investigations, how can measuring the internal energy of a substance help determine the time since a fire or explosion?

Answer: Measuring the internal energy can indicate how much heat was released or absorbed during a fire, helping estimate the temperature history and elapsed time since the event.

Question 1: A forensic team analyzes a burned piece of aluminum that was heated to 150°C before the fire. Post-fire analysis shows the aluminum's temperature dropped to 30°C. If the aluminum weighs 3 kg, estimate the internal energy loss assuming no heat loss to surroundings. Use the specific heat capacity of aluminum as 900 J/(kg·°C).

Answer: Energy lost = mass × specific heat capacity × temperature change = 3 kg × 900 J/(kg·°C) × (150°C - 30°C) = 3 kg × 900 J/(kg·°C) × 120°C = 324,000 J

Question 2: Explain what factors could affect the accuracy of this energy loss estimate in a real forensic situation.

Answer: Factors include heat loss to surroundings, incomplete heating, variations in material properties, and measurement errors in temperature or mass.

Question 1: Describe how the concept of internal energy relates to forensic evidence analysis, particularly in cases involving heat or fire. Include examples of how internal energy measurements can support or refute suspect claims about the timeline or nature of an event.

Answer: Internal energy reflects the thermal state of materials involved in forensic evidence. Measuring internal energy helps determine temperatures reached during fires or explosions, aiding in reconstructing timelines. For example, a higher internal energy in burned evidence indicates a more intense fire, which can support or challenge suspect claims. These measurements, combined with other evidence, help forensic scientists establish the sequence and severity of events.