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 = +

검증된 단계별 안내

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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주요 개념

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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.

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.

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.