Question

The process of evaporation of a liquid is accompanied by (1) increase in enthalpy (2) decrease in Gibbs energy (3) increase in entropy (4) all

Short answer

All (increase in enthalpy, decrease in Gibbs energy, and increase in entropy).

Step-by-step solution

Understand Evaporation

Evaporation is the process in which molecules transition from the liquid phase to the gas phase. During this process, the molecules gain kinetic energy sufficient to overcome intermolecular forces.

Analyze Changes in Enthalpy

During evaporation, heat is absorbed from the surroundings. This results in an increase in the enthalpy of the system, as energy is required to break the intermolecular bonds.

Evaluate Gibbs Energy

For a spontaneous process such as evaporation, the Gibbs free energy decreases. This indicates that the process will proceed naturally without requiring additional energy input.

Assess Entropy

Entropy, a measure of disorder, increases during evaporation because the gas phase of a substance is more disordered than its liquid phase. The molecules are moving more freely and randomly in the gaseous state.

Conclusion

Since evaporation results in an increase in enthalpy, a decrease in Gibbs energy, and an increase in entropy, it is correct to say that all three changes occur during the process of evaporation.

Key concepts

enthalpy change

When discussing the evaporation of a liquid, it’s essential to understand the concept of enthalpy. Enthalpy is a thermodynamic quantity that represents the total heat content of a system. When a liquid evaporates, it absorbs heat from its surroundings. This absorption of heat is necessary because energy is needed to break the intermolecular forces holding the liquid molecules together.
Specifically, during evaporation, you will notice an increase in enthalpy. This is because the system takes in heat, leading to a rise in energy level. Here is the core formula connected to enthalpy change:
\(\triangle H = Q \), where \(\triangle H\) is the change in enthalpy and \ Q \ is the heat absorbed.
Understanding this is key to grasping why substances feel cooler as they evaporate; they are pulling energy from their environment.

Gibbs free energy

Gibbs free energy (G) is a term used to predict the spontaneity of a process at constant temperature and pressure. It considers both enthalpy and entropy through the formula:
\(\triangle G = \triangle H - T\triangle S \), where \(\triangle G\) is the change in Gibbs free energy, \(\triangle H\) is the change in enthalpy, \(\triangle S\) is the change in entropy, and \ T \ is the temperature in Kelvin.
In the case of evaporation, for the process to be spontaneous (which evaporation generally is under standard conditions), the Gibbs free energy must decrease. This decrease signifies that the process will proceed naturally, without needing external energy input.
So when a liquid evaporates, the energy dynamics shift in such a way that the Gibbs free energy lessens, signaling a favorable process towards a state of equilibrium.

entropy increase

Entropy is a measure of disorder or randomness in a system. When a liquid evaporates, the molecules transition into a gas phase. This phase change results in an increase in entropy. Why? Because molecules in a gas phase have more freedom of movement compared to those in a liquid.
To put it simply, evaporating liquid molecules are no longer held together by strong intermolecular forces. They instead move freely and spread out in the gas phase, considerably increasing the disorder.
The formula to quantify entropy change is:
\(\triangle S = k_B \ ln\frac{W_{final}}{W_{initial}}\) where \ k_B \ is Boltzmann's constant, and \ W \ represents the number of microstates.
When enthalpy and entropy changes are combined into the Gibbs free energy equation, they help explain the spontaneity and thermodynamic favorability of processes like evaporation.