A piece of dry ice (solid CO2) is placed inside a balloon, and the balloon is tied shut. Over time, the carbon dioxide sub- limes, causing the balloon to increase in volume. Give the sign of the enthalpy change and the sign of work for the sublima-tion of CO2.

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Identify the process: Sublimation of CO2 involves the transition of solid carbon dioxide to its gaseous form within the sealed balloon.

Analyze the enthalpy change (\(\Delta H\)): Sublimation is an endothermic process, meaning it absorbs heat from the surroundings. Therefore, the sign of the enthalpy change (\(\Delta H\)) for the sublimation of CO2 is positive.

Consider the system and surroundings: The system is the CO2 and the balloon, while everything outside the balloon is the surroundings.

Determine the sign of work (w): As the CO2 sublimes and turns into gas, it expands against the balloon's elastic constraints, which means the system (CO2) is doing work on the surroundings (balloon). Work done by the system is considered negative.

Combine the concepts: The positive \(\Delta H\) indicates heat absorption, and the negative work (w) indicates that the system is expanding and doing work on its surroundings.

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Key Concepts

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

Sublimation

Sublimation is the phase transition in which a substance changes directly from a solid to a gas without passing through the liquid phase. In the case of dry ice (solid CO2), it absorbs heat from its surroundings to overcome intermolecular forces, leading to an increase in volume as it transforms into gaseous CO2.

Enthalpy Change (ΔH)

Enthalpy change (ΔH) refers to the heat content of a system at constant pressure. For sublimation, the process is endothermic, meaning it requires energy input, resulting in a positive enthalpy change. This indicates that heat is absorbed from the surroundings during the transition from solid to gas.

Work Done by the System

In thermodynamics, work done by the system is related to volume changes against external pressure. As the dry ice sublimates and the gas expands, the balloon's volume increases, doing work on the surroundings. This results in a positive sign for work, indicating that energy is transferred out of the system as the gas expands.

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