Chemistry - Chemical Equilibrium Question with Solution | TestHub
A cylinder fitted with a movable piston contains liquid ethanol in equilibrium with its vapour at 30°C. Which operation results in a decrease in the equilibrium vapour pressure?
Options:(select one or more)
Answer:
Solution:
At a fixed temperature, the equilibrium vapor pressure of pure ethanol remains constant. Moving the piston or adding more liquid only alters the amounts of liquid and vapor present; the pressure will return to its original value. Therefore, options (a) and (b) are incorrect.
Vapor pressure increases with temperature. Consequently, cooling the system will lower the vapor pressure, making option (c) correct.
Adding a non-volatile solute reduces the mole fraction of ethanol. According to Raoult's Law, the vapor pressure of the solution will decrease. Thus, option (d) is also correct.
The correct options are (c) and (d).
