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. (b) Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?

검증된 단계별 안내

Step 1: Identify the processes involved. In this case, we have the boiling of ethyl chloride (C2H5Cl) and the cooling of the surface.

Step 2: Recognize that the heat lost by the surface is gained by the ethyl chloride. This is an application of the law of conservation of energy, which states that energy cannot be created or destroyed, only transferred or transformed.

Step 3: Understand that the enthalpy of vaporization of ethyl chloride is involved. This is the energy required to convert a substance from a liquid to a gas at its boiling point. It is absorbed by the ethyl chloride as it vaporizes.

Step 4: Consider the enthalpy of cooling of the surface. This is the energy released by the surface as it cools down. It is transferred to the ethyl chloride.

Step 5: Note that the final temperature of the surface will be determined by the balance between these two enthalpies. If the enthalpy of vaporization of ethyl chloride is greater than the enthalpy of cooling of the surface, the surface will cool down. If it's less, the surface will heat up.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Enthalpy

Enthalpy is a thermodynamic property that represents the total heat content of a system. It is defined as the sum of the internal energy and the product of pressure and volume. In chemical processes, changes in enthalpy (ΔH) indicate the heat absorbed or released during reactions or phase changes, which is crucial for understanding heat transfer in the context of ethyl chloride cooling the surface.

Heat Transfer

Heat transfer refers to the movement of thermal energy from one object or substance to another due to a temperature difference. In this scenario, the heat lost by the warmer surface is transferred to the ethyl chloride, causing the surface to cool. Understanding the mechanisms of heat transfer—conduction, convection, and radiation—is essential for calculating the final temperature of the surface after contact with the ethyl chloride.

Phase Change

Phase change is the transition of a substance from one state of matter to another, such as from liquid to gas. In the case of ethyl chloride, when it is sprayed, it may evaporate, absorbing heat from the surface. The enthalpy of vaporization, which is the heat required to convert a unit mass of a liquid into vapor without a change in temperature, plays a critical role in determining how much heat is absorbed and how it affects the final temperature of the surface.