The vapour pressure of water at 20 degree celsius is 17.54 mmHg. What will be the vapour pressure of the water in the apparatus shown after the piston is lowered, decreasing the volume of the gas above the liquid to one half of its initial volume (assume temperature constant).
A) 8.77 mmHg
B)17.54mmHg
C)35.08 mmHg
D) between 8.77 and 17.54mmHg
Ans :
B) 17.54 mmHg
Volume does NOT affect vapour pressure !
The liquid in a container is in equilibrium with the vapor. When the volume is changed, for example - decreased, some of the vapor in the container turns into it's liquid state. Furthermore, if the volume is increased, some of the liquid will change into it's vapor state.