Ethyl chloride (C₂H₅Cl) boils at 12 °C. When liquid C₂H₅Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of C₂H₅Cl(g) as compared with that of C₂H₅Cl(l)?

Verified step by step guidance

1. Step 1: Understand the concept of specific heat. Specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The specific heat of a substance can vary depending on whether it is in a solid, liquid, or gaseous state.
2. Step 2: Analyze the given information. Ethyl chloride (C2H5Cl) boils at 12 °C, which means it changes from a liquid to a gas at this temperature. When liquid C2H5Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably.
3. Step 3: Understand the process of evaporation. When a liquid evaporates, it absorbs heat from its surroundings, causing a cooling effect. This is because the molecules with the highest kinetic energy are the ones most likely to escape from the liquid and become a gas, leaving the remaining liquid cooler.
4. Step 4: Compare the specific heats. The observation that the surface is cooled considerably when liquid C2H5Cl is sprayed on it suggests that the specific heat of C2H5Cl(g) is higher than that of C2H5Cl(l). This is because more heat is absorbed from the surroundings during the phase change from liquid to gas, indicating a higher specific heat in the gaseous state.
5. Step 5: Conclude the comparison. Therefore, the specific heat of gaseous ethyl chloride (C2H5Cl(g)) is higher than that of liquid ethyl chloride (C2H5Cl(l)).

Key Concepts

Phase Change and Boiling Point

The boiling point of a substance is the temperature at which it transitions from a liquid to a gas. Ethyl chloride has a boiling point of 12 °C, meaning it will vaporize at temperatures above this point. When sprayed on a warmer surface, the liquid ethyl chloride evaporates, absorbing heat from the surface, which leads to cooling. Understanding phase changes is crucial for analyzing thermal interactions in this scenario.

Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius. The observation that the surface cools when ethyl chloride is sprayed suggests that the gas phase (C2H5Cl(g)) has a lower specific heat capacity compared to the liquid phase (C2H5Cl(l)). This indicates that the gas can absorb heat more efficiently during the phase change, leading to a greater cooling effect.

Latent Heat of Vaporization

Latent heat of vaporization is the amount of energy required to convert a unit mass of a substance from liquid to gas at constant temperature. When ethyl chloride evaporates on the surface, it absorbs a significant amount of heat from the surroundings, which is related to its latent heat. This energy absorption during the phase change contributes to the cooling effect observed, highlighting the importance of latent heat in thermal processes.