Chapter U5.99, Problem 1TAI

Interpretation Introduction

Interpretation:The effect on heat during a phase change should be explained.

Concept Introduction:The water turns solid when left in the freezer for some time and ice cream melts when left at room temperature these are called phase changes. Boiling, melting, condensation, etc. are the process of phase changing.

Answer to Problem 1TAI

Heat transfer does not always result in a temperature increase. During a phase change, the transfer of energy into a substance does not cause any rise in temperature. Instead, this energy is used to overcome the attractions between atoms and molecules.

Explanation of Solution

Water boils at $100°\text{}\text{C}$ , at 1 atmosphere pressure. Once it reaches that temperature, liquid water does not get any hotter, no matter how big the flames are under its container or how much heat it.

When heat is transferred into a substance, like ice, the molecules in the ice move faster and the temperature rises. Once the temperature rises to $0°\text{}\text{C}$ , the ice begins melting. When heat is transferred into melting ice, the average kinetic energy does not change, and the temperature does not rise. Now, it is clear that heat transfer does not always result in a temperature change.

Conclusion

When a substance changes phase from solid to liquid or from liquid to gas, a certain amount of energy must be supplied to overcome the molecular or ionic attractions between the particles.