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Ch.19 - Chemical Thermodynamics
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 15th EditionCh.19 - Chemical ThermodynamicsProblema 2
Capitolo 19, Problema 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?

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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.

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

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

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