Calculations and Phase Diagrams Notes

Calculating Heat Involved in Phase Changes of Bromoethane

• Given:
  • Mass of bromoethane: $100 \text{ g}$
  • Melting point: $-7.0 \,^{\circ}\text{C}$
  • Boiling point: $59.0 \,^{\circ}\text{C}$
  • Specific heat of liquid bromoethane: $0.474 \,\frac{\text{J}}{\text{g} \cdot ^{\circ}\text{C}}$
  • Heat of fusion: $10.8 \,\frac{\text{kJ}}{\text{mol}}$
  • Heat of vaporization: $29.6 \,\frac{\text{kJ}}{\text{mol}}$

Phase Change Diagram Analysis

• Given:
  • Mass of substance: $20.0 \text{ g}$

Analyzing the Provided Phase Change Diagram

1. Boiling Point Temperature:

   • The boiling point of the substance is at $80\,^{\circ}\text{C}$.

2. Calculating Heat of Fusion:

   • The heat of fusion is the amount of heat required to change the substance from solid to liquid at its melting point.
   • From the graph, the heat added during melting (section B to C) is $100 \text{ J}$.
   • Heat of fusion calculation:
     $\text{Heat of fusion} = \frac{\text{Heat}}{\text{Mass}} = \frac{100 \text{ J}}{20.0 \text{ g}} = 5.0 \,\frac{\text{J}}{\text{g}}$

3. Physical State at $55\,^{\circ}\text{C}$:

   • At $55\,^{\circ}\text{C}$, the substance would be in the liquid state, as it is between the melting and boiling points.

4. Process from C to B:

   • The section from "C" to "B" of the diagram refers to the heat being removed during freezing or solidification. The substance is changing from liquid to solid at its freezing point.

5. Physical State after Removing 200 J from $60\,^{\circ}\text{C}$:

   • The substance starts at $60\,^{\circ}\text{C}$, which is in the liquid state (above the melting point but below the boiling point).
   • Removing $200 \text{ J}$ of heat brings the substance to point L, based on heat quantities on the X-axis. Since point L is along the sloped line after point D, it indicates after solidifying it cooled further.
   • Therefore, the substance would be in the solid state.