The normal boiling point of Br2(l) is 58.8 ^∘ C, and its molar enthalpy of vaporization is ΔHvap

step 1 We have the normal boiling point of bromine as 58 .8 degrees Celsius, while the molar enthalpy o

The normal boiling point of Br2(l) is 58.8 ^∘ C, and its...

The normal boiling point of $\mathrm{Br}_{2}(l)$ is $58.8{ }^{\circ} \mathrm{C},$ and its molar enthalpy of vaporization is $\Delta H_{\text {vap }}=29.6 \mathrm{~kJ} /$ mol. (a) When $\mathrm{Br}_{2}(l)$ boils at its normal boiling point, does its entropy increase or decrease? (b) Calculate the value of $\Delta S$ when $1.00 \mathrm{~mol}$ of $\mathrm{Br}_{2}(l)$ is vaporized at $58.8{ }^{\circ} \mathrm{C}$.

Key Concepts

Thermodynamic Relationship (?S = ?H/T)

This key relationship connects the enthalpy change and the entropy change during a reversible process at a constant temperature. In the context of vaporization, it provides a straightforward method to calculate the change in entropy by dividing the enthalpy of vaporization by the absolute temperature (in Kelvin) at which the transition takes place.

Phase Transitions

This concept involves the change of a substance from one phase to another, like liquid to gas. During a phase transition, particularly when vaporization occurs, the system transitions from a more ordered phase (liquid) to a less ordered phase (gas), which reflects a change in the molecular arrangement and intermolecular forces.

Entropy

Entropy is a measure of the disorder or randomness of a system. During processes such as vaporization, entropy increases because gas molecules have significantly more freedom of movement and a greater number of available microstates compared to those in the liquid state, leading to a net increase in randomness.

Enthalpy of Vaporization

Enthalpy of vaporization is the heat required to convert a given amount of a liquid into gas at constant pressure. This concept is essential in thermodynamics because it quantifies the energy change associated with breaking the intermolecular forces in the liquid, thereby facilitating the phase change to vapor.

Normal Boiling Point

The normal boiling point is defined as the temperature at which the vapor pressure of a liquid equals the external pressure (typically 1 atm). At this point, the liquid has enough thermal energy to overcome intermolecular attractions and transition into the gaseous phase.

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