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Chapter 11: Problem 42

Ethyl chloride \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\right)\) boils at \(12^{\circ} \mathrm{C}\). When liquid \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\) under pressure is sprayed on a room-temperature \(\left(25^{\circ} \mathrm{C}\right)\) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(g)\) as compared with \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(l) ?\) (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?

Short Answer

Expert verified
The cooling effect observed when liquid ethyl chloride is sprayed on a room-temperature surface indicates that the specific heat of ethyl chloride in the gaseous state is higher than in the liquid state since the evaporation requires heat energy. To calculate the final temperature of the surface, we need to consider the following enthalpies: 1) the heat transfer from the surface to the ethyl chloride due to the change in temperature, and 2) the enthalpy of vaporization of liquid ethyl chloride as it absorbs heat to go from the liquid state to the gaseous state.

Step by step solution

01

(a) Comparing specific heats of ethyl chloride in gas and liquid states

When liquid ethyl chloride evaporates and goes into the gaseous state, it absorbs heat from the surface. This heat absorption is a strong indicator that the specific heat of ethyl chloride in the gaseous state is higher than in the liquid state. This is because the evaporation requires heat energy to break the bonds between the molecules; hence ethyl chloride has higher specific heat in the gas state. Now, let's move to part (b) of the problem:
02

(b) Considering enthalpies involved

Since we are assuming that the heat lost by the surface is gained by the ethyl chloride, we have to consider the enthalpies involved in this process. The following enthalpies should be considered: 1. The heat transfer (\(q\)) from the surface to the ethyl chloride due to the change in temperature of the surface. 2. The enthalpy of vaporization (\(∆H_{vap}\)) of liquid ethyl chloride as it absorbs heat to go from the liquid state to the gaseous state. By considering these enthalpies, we can calculate the final temperature of the surface using the energy conservation concept and knowing the specific heats and masses of the surface and ethyl chloride involved in the process.

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