A 15.0-kg block of ice at 0.0°C melts to liquid water at 0.0°C inside a large room at 20.0°C. Treat the ice and the room as an isolated system, and assume that the room is large enough for its temperature change to be ignored. (a) Is the melting of the ice reversible or irreversible? Explain, using simple physical reasoning without resorting to any equations.

Verified step by step guidance

1. Identify the initial state of the system, which includes the ice at 0.0°C and the room at 20.0°C.
2. Recognize that the ice absorbs heat from the room to melt, transitioning from solid to liquid while remaining at 0.0°C.
3. Understand that the process involves heat transfer from a warmer body (the room) to a colder body (the ice), which aligns with the second law of thermodynamics stating that heat flows naturally from hot to cold.
4. Consider whether the process can spontaneously reverse, i.e., if the water can turn back into ice without external work or energy removal from the system. Since this would require heat to flow from the colder water to the warmer room spontaneously, it contradicts the natural heat flow direction.
5. Conclude that the melting of the ice is an irreversible process because it cannot spontaneously reverse under the given conditions, and it results in an increase in the entropy of the system.

Key Concepts

Phase Change

Phase change refers to the transition of a substance from one state of matter to another, such as from solid to liquid. In this scenario, the ice is undergoing a phase change as it melts into water. This process involves the absorption of heat energy, which breaks the bonds holding the ice molecules in a rigid structure, allowing them to move freely as liquid water.

Reversibility in Thermodynamics

In thermodynamics, a process is considered reversible if it can be reversed without leaving any change in the system or surroundings. Melting ice in a warm room is typically irreversible because once the ice melts, the water cannot spontaneously return to ice at the same temperature without external intervention, such as cooling the water below freezing.

Entropy

Entropy is a measure of disorder or randomness in a system. When ice melts, the entropy of the system increases because the liquid water has more molecular disorder compared to the structured arrangement of ice. This increase in entropy is a key factor in determining the irreversibility of the melting process, as natural processes tend to move towards states of higher entropy.