Problem 21 - Chemistry: An Atoms-Focused Approach

Question

What happens to the internal energy of a liquid at its boiling point when it vaporizes?

Step-by-Step Solution

Answer

A: During vaporization at its boiling point, the internal energy of a liquid increases as it absorbs energy to overcome intermolecular forces, resulting in the liquid converting into a gas. The exact change in internal energy depends on the specific substance (liquid) and the amount of it that vaporizes, which can be calculated using the equation: ∆U = n × ∆Hvap.

Step 1: Understand internal energy, boiling point, and vaporization

Internal energy is a measure of the total kinetic and potential energy of the molecules in a substance. In the context of a liquid at its boiling point, the internal energy is related to the motion and attractions between the liquid's molecules. The boiling point is the temperature at which a liquid turns into a vapor or gas. During vaporization, the liquid absorbs energy to overcome the intermolecular forces holding it together, which allows the molecules to move freely and turn into a gas.

Step 2: Calculate the change in internal energy during vaporization

To calculate the internal energy change during vaporization, we need to consider the following: - The substance (liquid) and its specific properties, such as its molar heat of vaporization \((\Delta H_{vap})\), which is the amount of energy required per mole to vaporize the liquid at its boiling point. - The number of moles \((n)\) of the liquid that vaporizes. The change in internal energy \((\Delta U)\) can be calculated using the equation: \(\Delta U = n \times \Delta H_{vap}\)

Step 3: Conclusion

When a liquid at its boiling point vaporizes, its internal energy increases as it needs to absorb energy to overcome intermolecular forces. This increase in internal energy results in the liquid converting into a gas. The exact change in internal energy depends on the specific substance (liquid) and the amount of it that vaporizes, which can be calculated using the above equation.