Question 1: Define the term 'melting point'.

Answer: The temperature at which a solid turns into a liquid under constant pressure.

Question 2: Explain the difference between vaporization and boiling.

Answer: Vaporization is the process of a liquid turning into vapor, which includes evaporation (occurs at the surface at any temperature) and boiling (occurs throughout the liquid at a specific temperature).

Question 3: Describe what occurs at the molecular level during sublimation.

Answer: Sublimation occurs when molecules transition directly from the solid phase to the gas phase without passing through the liquid phase, involving molecules gaining enough energy to overcome intermolecular forces.

Question 1: Calculate the amount of heat energy required to melt 50 grams of ice at 0°C. (Specific heat of fusion of ice = 334 J/g)

Answer: 16700 Joules

Question 2: A sample of water at 100°C is heated to produce 200 grams of steam at 100°C. How much energy is required? (Latent heat of vaporization of water = 2260 J/g)

Answer: 452,000 Joules

Question 1: Describe a simple experiment to demonstrate sublimation of dry ice. Include the key variables that need to be controlled.

Answer: Place dry ice in a sealed container in a well-ventilated area and observe the direct transition from solid to gas. Control variables include temperature, pressure, and ventilation to ensure safety and accurate observation.

Question 2: Identify two safety precautions students should follow when conducting experiments involving high temperatures or sublimation.

Answer: Wear protective gloves and goggles; ensure proper ventilation to avoid inhaling vapors.

Question 1: A sample of sulfur is heated from 25°C to 120°C. At 115°C, it sublimates completely. Describe what this indicates about sulfur's sublimation point and the conditions required.

Answer: Sulfur's sublimation point is around 115°C under the given pressure. Complete sublimation at this temperature indicates that sulfur can transition directly from solid to gas without becoming liquid if conditions are right.

Question 2: Explain how understanding phase changes is important in the industrial process of distillation.

Answer: Distillation relies on differences in boiling points to separate mixtures. Knowing the precise temperatures at which substances vaporize allows industries to efficiently and safely separate components, such as in refining crude oil or producing purified chemicals.

Question 1: How does understanding the latent heat of vaporization help in designing better refrigeration systems?

Answer: It helps determine how much energy is needed to convert refrigerant from liquid to vapor, ensuring efficient cooling cycles and energy conservation in refrigeration systems.

Question 2: Describe a day-to-day scenario where phase changes are crucial for safety or efficiency.

Answer: In cooking, boiling water involves vaporization; understanding the boiling point ensures food is cooked properly. In safety, knowing how steam expands during boiling helps prevent accidents like explosions in pressure cookers.