Question 59 OSV01 - Master/Chief Mate - Offshore Supply Vessels

The Correct Answer is B **Explanation for Option B (Correct):** Vapor pressure is the pressure exerted by the vapor of a substance when the substance is in equilibrium with its liquid (or solid) phase in a closed container. When the temperature of a liquid increases, the average kinetic energy of the molecules also increases. This higher energy allows more molecules to overcome the intermolecular forces holding them in the liquid phase and escape into the gas (vapor) phase. Because more molecules are transitioning into the vapor phase, the concentration of vapor molecules above the liquid increases, which results in a corresponding increase in the pressure exerted by the vapor. Therefore, the vapor pressure of a substance is directly proportional to its temperature. **Explanation for Other Options (Incorrect):** * **A) The pressure decreases as temperature increases:** This is the opposite of the observed physical behavior. Higher temperatures provide the energy necessary to create more vapor, thus increasing the pressure, not decreasing it. * **C) The pressure is not affected by temperature:** This is incorrect. Temperature is the primary factor determining the kinetic energy of the molecules and their ability to escape the liquid phase; therefore, temperature significantly affects vapor pressure. * **D) The pressure may increase or decrease as the temperature rises:** While other factors (like atmospheric pressure or volume changes in an open system) can influence things, the intrinsic vapor pressure of a pure substance at equilibrium always increases monotonically (continuously upward) as its temperature rises. There is no physical mechanism by which increasing the temperature would decrease the equilibrium vapor pressure.