Question

Describe what the heating curve of ethanol shows about the rate of temperature increase and the enthalpy of vaporization.
A) The temperature increase converts bonding forces into intermolecular forces.
Eliminate
B) The faster the rate temperature increase then the faster the enthalpy occurs.
C) The enthalpy of vaporization is unaffected by the rate of temperature increase.
D) The rate for both the temperature increase and the enthalpy change are the same.

Answer 1

Answer: -

A heating curve is one that plots the temperature of a system as a function of the heat flow into the system.

During a phase change, the temperature does not change. But heat flows into the system. This heat is called the enthalpy of fusion.

Only after melting is complete that further heat increases the temperature.

Thus option D is incorrect.

Option C is incorrect as the enthalpy of vaporization is temperature dependent.

Option A is incorrect as temperature increase increases the kinetic energy.

Option B is correct as the faster the rate temperature increase then the faster the enthalpy occurs in accordance with Kirchhoff's Law.

Answer 2

The correct answer is B.) The enthalpy of vaporization is unaffected by the rate of temperature increase..

The temperature does not change during the phase change so the rate of temperature increase will not affect the enthalpy. We can see this from the zero slope line (horizontal line) during the enthalpy of vaporization.