Question

Acetone evaporates more quickly than water at room temperature. What can you say about the relative strength of the intermolecular forces in the two compounds? Which substance is more volatile?

Short answer

Acetone has weaker intermolecular forces than water, which makes it more volatile.

Step-by-step solution

Identify the Key Concepts

Understand that the rate of evaporation is affected by the strength of intermolecular forces. A substance that evaporates quickly has weaker intermolecular forces than a substance that evaporates more slowly.

Analyze the Observation

Since acetone evaporates more quickly than water at room temperature, it implies that the intermolecular forces in acetone are weaker than those in water.

Conclude About Volatility

Substances with weaker intermolecular forces tend to be more volatile. Therefore, acetone is more volatile than water.

Key concepts

Evaporation Rate

Evaporation is the process in which a liquid turns into a vapor. A key factor affecting the evaporation rate is the strength of intermolecular forces within a liquid. Intermolecular forces are the forces of attraction between molecules, which keep a substance in its liquid or solid form.

When these forces are weak, molecules can escape from the liquid more easily, leading to a higher evaporation rate. In contrast, strong intermolecular forces tend to hold the molecules together more tightly, which reduces the evaporation rate. Several factors, such as temperature, surface area, and pressure, also play a role in evaporation but the intrinsic strength of the intermolecular forces within the substance is a primary determinant of how quickly it will evaporate under any given set of conditions.

Volatility

Volatility is a term that often describes how readily a substance will vaporize, which is inherently related to its evaporation rate. Essentially, volatility is a measure of a substance's tendency to turn into gas or vapor. This is crucial in many industries, such as perfume manufacturing, where a high degree of volatility is desirable for a scent to be detected by our sense of smell.

In terms of chemistry, a volatile substance has weak intermolecular forces; this means it requires less energy for the molecules to overcome these forces and transition from liquid to gas. Volatility is not constant and can change depending on factors such as temperature and pressure. As temperature increases, for example, volatility tends to increase because the molecules have more energy to overcome intermolecular forces.

Comparing Acetone and Water

When comparing the intermolecular forces of acetone and water, it is clear that they behave differently due to the nature of their molecular structures and interactions. Water is known for its relatively strong hydrogen bonds; these are a type of intermolecular force that arise because of the attraction between the positive end of one water molecule and the negative oxygen end of another. This strong bonding keeps water in its liquid state for a wide range of temperatures and is responsible for water's relatively high boiling point. It also results in a slower evaporation rate compared to many other substances.

Acetone, on the other hand, although it can form weak hydrogen bonds, is primarily governed by dipole-dipole interactions and London dispersion forces, which are generally weaker than the hydrogen bonds in water. This weaker force translates to a higher volatility for acetone, explaining why it evaporates more quickly than water at the same temperature. Understanding these differences is key in applications ranging from industrial solvents to nail polish removers, where the quick evaporation of acetone is a beneficial property.