The normal freezing point of n-octane (C₈H₁₈) is -57 °C. (d) Is there any temperature at which liquid n-octane and solid n-octane are in equilibrium? Explain.

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1. 1. The freezing point of a substance is the temperature at which the liquid and solid phases of the substance are in equilibrium. This means that at this temperature, the rate at which the substance freezes (goes from liquid to solid) is equal to the rate at which it melts (goes from solid to liquid).
2. 2. For n-octane, this temperature is -57 °C. Therefore, at -57 °C, liquid n-octane and solid n-octane are in equilibrium.
3. 3. At temperatures above -57 °C, n-octane will be in the liquid phase because the rate of melting will be greater than the rate of freezing. At temperatures below -57 °C, n-octane will be in the solid phase because the rate of freezing will be greater than the rate of melting.
4. 4. Therefore, there is only one temperature at which liquid n-octane and solid n-octane are in equilibrium, and that is at its freezing point of -57 °C.
5. 5. In conclusion, the freezing point of a substance is the temperature at which the liquid and solid phases of the substance are in equilibrium. For n-octane, this temperature is -57 °C.

Key Concepts

Phase Equilibrium

Phase equilibrium occurs when two phases of a substance, such as solid and liquid, coexist at a specific temperature and pressure. At this point, the rates of melting and freezing are equal, leading to a stable condition where both phases are present. For n-octane, this equilibrium can be established at its freezing point, where the solid and liquid forms can exist together.

Freezing Point

The freezing point is the temperature at which a liquid turns into a solid under a given pressure. For n-octane, the normal freezing point is -57 °C, meaning that at this temperature, n-octane can exist as both a liquid and a solid. Understanding this concept is crucial for determining the conditions under which n-octane can transition between its phases.

Thermodynamic Stability

Thermodynamic stability refers to the state of a system where it is at its lowest energy configuration, making it resistant to change. In the context of n-octane, the equilibrium between its solid and liquid phases represents a stable state at the freezing point. Any deviation from this temperature will favor either the solid or liquid phase, illustrating the importance of temperature in phase behavior.