a. The triple point of benzene is at 5.5^∘ C and 4.8 kPa . The critical point is at 289^∘ C and

step 1 We look at a phase diagram for benzene. We have temperature on the bottom, pressure on the side

A. The triple point of benzene is at 5.5^∘ C and 4.8 kPa ....

a. The triple point of benzene is at $5.5^{\circ} \mathrm{C}$ and 4.8 $\mathrm{kPa}$ . The critical point is at $289^{\circ} \mathrm{C}$ and $4.29 \times 10^{3} \mathrm{kPa}$ . Vapor pressure above solid benzene is 101.3 $\mathrm{kPa}$ at $80.1^{\circ} \mathrm{C}$ . Solid benzene is denser than liquid benzene. Sketch the phase diagram of benzene.. b. In what state is benzene at 200 $\mathrm{kPa}$ and $80^{\circ} \mathrm{C} ?$ c. In what state is benzene at 10 $\mathrm{kPa}$ and $100^{\circ} \mathrm{C} ?$ d. What happens as you increase the temperature of a sample of benzene at 101.3 $\mathrm{kPa}$ from $0^{\circ} \mathrm{C}$ to $20^{\circ} \mathrm{C}$ ? e. What happens as you decrease the pressure on a sample of benzene at $80^{\circ} \mathrm{C}$ from 150 $\mathrm{kPa}$ to 100 $\mathrm{kPa} ?$

a. The triple point of benzene is at $5.5^{\circ} \mathrm{C}$ and 4.8 $\mathrm{kPa}$ . The critical point is at $289^{\circ} \mathrm{C}$ and $4.29 \times 10^{3} \mathrm{kPa}$ . Vapor pressure above
solid benzene is 101.3 $\mathrm{kPa}$ at $80.1^{\circ} \mathrm{C}$ . Solid benzene is denser than liquid benzene. Sketch the phase diagram of benzene..
b. In what state is benzene at 200 $\mathrm{kPa}$ and $80^{\circ} \mathrm{C} ?$
c. In what state is benzene at 10 $\mathrm{kPa}$ and $100^{\circ} \mathrm{C} ?$
d. What happens as you increase the temperature of a sample of benzene at 101.3 $\mathrm{kPa}$ from $0^{\circ} \mathrm{C}$ to $20^{\circ} \mathrm{C}$ ?
e. What happens as you decrease the pressure on a sample of benzene at $80^{\circ} \mathrm{C}$
from 150 $\mathrm{kPa}$ to 100 $\mathrm{kPa} ?$

Key Concepts

Density and Phase Equilibria

Density differences between phases, such as when a solid is denser than its corresponding liquid, can result in unique phase behavior and stability. These differences play a significant role in determining phase boundaries and are reflected in the slopes of the phase lines on a phase diagram.

Phase Transitions

Phase transitions are the changes between different states of matter—such as fusion (melting), vaporization (boiling), and sublimation—that occur when a substance absorbs or releases energy. These transitions are depicted in phase diagrams and are governed by the thermodynamic conditions of temperature and pressure.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It is an important concept for understanding evaporation, boiling, and condensation, and it is used to determine phase boundaries in phase diagrams.

Triple Point

The triple point is the unique condition where solid, liquid, and gas phases of a substance coexist in thermodynamic equilibrium. It is an important parameter in thermodynamics and phase diagrams because it provides a fundamental reference point for calibrating temperature scales and for understanding phase stability.

Phase Diagram

A phase diagram is a graphical representation that shows the conditions of temperature and pressure at which different phases (solid, liquid, and gas) of a substance occur and coexist in equilibrium. It includes boundaries that indicate phase transitions and key reference points, helping to understand and predict the state of a substance under various conditions.

Critical Point

The critical point marks the end of the liquid–vapor phase boundary. Above this point, the distinction between the liquid and vapor phases disappears, and the substance forms a supercritical fluid, which exhibits properties of both phases. This concept is crucial in understanding the behavior of substances near the critical conditions.

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