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Ch.19 - Chemical Thermodynamics
All textbooksBrown 15th EditionCh.19 - Chemical ThermodynamicsProblem 2
Chapter 19, Problem 2

As shown here, one type of computer keyboard cleaner contains liquefied 1,1-difluoroethane (C2H4F2), which is a gas at atmospheric pressure. When the nozzle is squeezed, the 1,1-difluoroethane vaporizes out of the nozzle at high pressure, blowing dust out of objects. (d) Given your answers to (a), (b), and (c), do you think the operation of this product depends more on enthalpy or entropy? (a) Based on your experience, is the vaporization a spontaneous process at room temperature?

Verified step by step guidance
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Step 1: Understand the process of vaporization. Vaporization is the phase transition from liquid to gas. For a process to be spontaneous, the change in Gibbs free energy (\( \Delta G \)) must be negative. The equation \( \Delta G = \Delta H - T\Delta S \) relates Gibbs free energy to enthalpy (\( \Delta H \)) and entropy (\( \Delta S \)).
Step 2: Consider the spontaneity of vaporization at room temperature. At room temperature, vaporization is generally spontaneous for many substances, including 1,1-difluoroethane, because the increase in entropy (\( \Delta S \)) when a liquid becomes a gas often outweighs the enthalpy change (\( \Delta H \)).
Step 3: Analyze the role of enthalpy (\( \Delta H \)) in the process. Enthalpy change during vaporization is typically positive because energy is required to overcome intermolecular forces in the liquid state. However, this energy input is often offset by the entropy increase.
Step 4: Analyze the role of entropy (\( \Delta S \)) in the process. The transition from a more ordered liquid state to a less ordered gaseous state results in a significant increase in entropy, which is a key driver for the spontaneity of vaporization.
Step 5: Conclude whether the operation depends more on enthalpy or entropy. Given the significant increase in entropy during vaporization, the process likely depends more on entropy than enthalpy, as the disorder introduced by the gas phase is a major factor in the spontaneity of the process.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enthalpy

Enthalpy is a thermodynamic property that reflects the total heat content of a system. It is often associated with the heat absorbed or released during a chemical reaction or phase change at constant pressure. In the context of vaporization, a positive change in enthalpy indicates that energy is required to overcome intermolecular forces, making the process endothermic.
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Entropy

Entropy is a measure of the disorder or randomness in a system. It quantifies the number of ways a system can be arranged, with higher entropy indicating greater disorder. During vaporization, the transition from liquid to gas significantly increases entropy, as gas molecules have more freedom of movement compared to liquid molecules, contributing to the spontaneity of the process.
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Spontaneity of Processes

A process is considered spontaneous if it occurs without external intervention, often driven by changes in enthalpy and entropy. The Gibbs free energy equation (ΔG = ΔH - TΔS) helps determine spontaneity, where a negative ΔG indicates a spontaneous process. In the case of vaporization, if the increase in entropy outweighs the enthalpy change, the process is likely spontaneous at room temperature.
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Related Practice
Textbook Question

Two different gases occupy the two bulbs shown here. Consider the process that occurs when the stopcock is opened, assuming the gases behave ideally. (d) How does the process affect the entropy of the surroundings?

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Textbook Question

b. If energy can flow in and out of the system to maintain a constant temperature during the process, what can you say about the entropy change of the surroundings as a result of this process?

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Textbook Question

Predict the signs of ΔH and ΔS for this reaction. Explain your choice.

Textbook Question

The accompanying diagram shows how entropy varies with temperature for a substance that is a gas at the highest temperature shown. (c) If this substance is a perfect crystal at T = 0 K, what is the value of S at this temperature?

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