Lowering of vapor pressure is directly proportional to:
a) Temperature
b) Mole fraction of Solute
c) Mole fraction of Solvent
d) Amount of solution
To determine which of the given factors is directly proportional to the lowering of vapor pressure, we need to understand the concept of vapor pressure lowering.
Vapor pressure is the pressure exerted by the vapor molecules above a liquid when the liquid and vapor are in dynamic equilibrium. When a non-volatile solute (i.e., a substance that does not easily evaporate) is dissolved in a solvent, the vapor pressure of the resulting solution is lower than that of the pure solvent alone. This reduction in vapor pressure is known as vapor pressure lowering.
Now, let's analyze each option to see which one is directly proportional to the vapor pressure lowering.
a) Temperature: The vapor pressure of a liquid generally increases with temperature. Hence, an increase in temperature doesn't lead to a lowering of vapor pressure.
b) Mole fraction of Solute: The mole fraction of solute refers to the ratio of moles of solute to the total moles of solute and solvent in the solution. The presence of more solute particles decreases the vapor pressure since the solvent molecules are replaced by the solute particles on the surface. Increasing the mole fraction of solute leads to a higher vapor pressure lowering.
c) Mole fraction of Solvent: The mole fraction of solvent is the ratio of moles of solvent to the total moles of solute and solvent in the solution. The presence of more solvent molecules doesn't directly affect the vapor pressure lowering. Instead, it is the presence of solute particles that contribute to the vapor pressure reduction.
d) Amount of solution: The amount of solution, also known as the total volume of the solution, does not directly affect the vapor pressure lowering. It is the nature and quantity of solute particles that determine the magnitude of the vapor pressure reduction.
Based on the above analysis, the correct answer is b) Mole fraction of Solute. As the mole fraction of the solute increases, the vapor pressure lowering also increases.