Ch.9 - Thermochemistry: Chemical Energy

McMurry8th EditionChemistryISBN: 9781292336145Non è quello che usi tu?Cambia libro di testo

McMurry 8th Edition

Ch.9 - Thermochemistry: Chemical Energy

Problema 2

Capitolo 9, Problema 2

A room-temperature balloon filled with air is placed in the freezer and the balloon contracts. What is the sign of q and w for the air inside the balloon? (LO 9.4) (a) q = +, w = - (b) q = +, w = + (c) q = -, w = - (d) q = -, w = +

Guida verificata passo dopo passo

insert step 1> Understand the concepts of q (heat) and w (work) in thermodynamics. In this context, q represents the heat exchanged with the surroundings, and w represents the work done by or on the system.

insert step 2> Consider the process: the balloon is placed in the freezer, which means it is losing heat to the surroundings. Therefore, the sign of q should be negative (q = -).

insert step 3> Analyze the work done: as the balloon contracts, the volume of the gas inside decreases. In thermodynamics, when a gas contracts, it means work is done on the system by the surroundings. Therefore, the sign of w should be positive (w = +).

insert step 4> Combine the signs of q and w based on the analysis: since q is negative and w is positive, the correct choice is (d) q = -, w = +.

insert step 5> Review the options and confirm that the correct answer is (d) q = -, w = +, as it matches the analysis of heat loss and work done on the system.

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Thermodynamics

Thermodynamics is the study of energy transfer and transformation. In this context, it helps us understand how heat (q) and work (w) interact in a system, such as the air inside the balloon. The first law of thermodynamics states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

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Percorso guidato

01:18

First Law of Thermodynamics

Heat Transfer (q)

Heat transfer (q) refers to the energy exchanged between a system and its surroundings due to a temperature difference. In this scenario, when the balloon is placed in the freezer, the air inside loses heat to the colder environment, resulting in a negative value for q, indicating that the system is losing energy.

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00:44

Heat Capacity

Work Done (w)

Work (w) in thermodynamics is defined as the energy transferred when a force is applied over a distance. For a gas in a balloon, work is done on the gas when the external pressure compresses it. In this case, as the balloon contracts due to the decrease in temperature, the air inside does negative work on the surroundings, leading to a negative value for w.

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Percorso guidato

01:52

Work Function Calculation Example

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Several processes are given in the table and labeled as endo- thermic or exothermic and given a sign for ∆H°. Which process is labeled with the correct sign of ∆H° and correct classification as endothermic or exothermic? (LO 9.8) Process (a) Ammonium nitrate dissolves in water, and the temperature of the solution decreases.

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