Question

What is the property of vapor pressure lowering, and what equation is used to determine its effect?

Answer 1

Dissolving a nonvolatile substance in a volatile liquid lowers the vapor pressure. This is due to reduced surface area available to solvent molecules, resulting in less solvent vaporization. The Clausius-Clapeyron equation describes the relationship between vapor pressure and temperature.

Step-by-step explanation:

Dissolving a nonvolatile substance in a volatile liquid results in a lowering of the liquid's vapor pressure. This is due to the effect of added solute molecules on the liquid's vaporization and condensation processes. The presence of solute reduces the surface area available to solvent molecules, decreasing the rate of solvent vaporization. The net result is that the vaporization-condensation equilibrium is achieved with fewer solvent molecules in the vapor phase, causing a lower vapor pressure.

The quantitative relation between a substance's vapor pressure and its temperature is described by the Clausius-Clapeyron equation.

Answer 2

The property of vapor pressure lowering is known as Raoult's Law. The equation used to determine its effect is expressed as
`( P_{\text{soln}} = x_{\text{A}} \cdot P_{\text{A}} + x_{\text{B}} \cdot P_{\text{B}} \), where \( P_{\text{soln}} \))` is the vapor pressure of the solution,
`\( x_{\text{A}} \) and \( x_{\text{B}} \)` are the mole fractions of the components A and B, and
`\( P_{\text{A}} \) and \( P_{\text{B}} \)` are the vapor pressures of pure A and B.

Step-by-step explanation:

Raoult's Law describes the vapor pressure lowering of a solution compared to the vapor pressure of its individual components. It is especially relevant in ideal solutions where the intermolecular forces between different molecules are similar. The equation
`\( P_{\text{soln}} = x_{\text{A}} \cdot P_{\text{A}} + x_{\text{B}} \cdot P_{\text{B}} \)` quantifies this effect.

Breaking down the equation,
`\( P_{\text{soln}} \)` is the vapor pressure of the solution,
`\( x_{\text{A}} \) and \( x_{\text{B}} \)` represent the mole fractions of components A and B, and
`\( P_{\text{A}} \) and \( P_{\text{B}} \)` are the vapor pressures of pure A and B, respectively. The mole fraction accounts for the proportion of each component in the solution.

In practical terms, Raoult's Law is applied to understand and predict the behavior of solutions, especially when there is a deviation from ideal behavior. The equation aids in calculating the vapor pressure of the solution based on the vapor pressures of its individual components and their respective mole fractions.