Consider a system consisting of an ice cube. (a) Under what conditions can the ice cube melt reversibly?

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Identify the concept of reversible processes in thermodynamics, which occur when a system changes state in such a way that the process can be reversed by an infinitesimal change in a variable.

Recognize that for the ice cube to melt reversibly, the system must be in thermal equilibrium with its surroundings, meaning the temperature of the ice cube and the surroundings must be the same.

Understand that the melting point of ice is 0°C (273.15 K) at 1 atm pressure, so the surroundings must also be at this temperature for reversible melting.

Consider that the pressure should remain constant at 1 atm, as changes in pressure can affect the melting point of ice.

Ensure that the heat exchange between the ice cube and its surroundings is infinitesimally slow, allowing the system to remain in equilibrium throughout the process.

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Key Concepts

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

Reversible Processes

A reversible process is a thermodynamic process that can be reversed without leaving any trace on the surroundings. In the context of melting ice, this means that the ice can transition to water and back to ice without any net change in the system or its environment. Reversible processes occur under specific conditions, typically involving equilibrium and infinitesimally slow changes.

Phase Equilibrium

Phase equilibrium refers to the state in which multiple phases of a substance (like solid ice and liquid water) coexist at a specific temperature and pressure. For an ice cube to melt reversibly, it must be at the melting point (0°C at 1 atm) where the solid and liquid phases are in equilibrium. Any deviation from this equilibrium can lead to irreversible changes.

Thermodynamic Conditions

The thermodynamic conditions, including temperature and pressure, play a crucial role in determining whether a phase change, such as melting, can occur reversibly. For an ice cube to melt reversibly, it must be subjected to conditions where the temperature is maintained at the melting point and the pressure is constant, allowing for the absorption of heat without changing the overall state of the system.

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A system goes from state 1 to state 2 and back to state 1. (c) Suppose the changes in state are reversible processes. Is the work done by the system upon going from state 1 to state 2 the same or different as compared to that upon going from state 2 back to state 1?

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