Ice and water are placed in a closed container at a pressure of 1 atm and temperature 273.15 K. If pressure of the system is increased 2 times, keeping temperature constant, then identify correct observation from following
- Liquid phase disappears completely.
- The amount of ice decreases.
- The solid phase (ice) disappears completely.
- Volume of system increases.
Answer
(3) The solid phase (ice) disappears completely.
Solution
At 1 atm and 273.15 K, ice and water are in equilibrium: H2O(s) H2O(l)
Ice has a lower density (larger volume) than water, melting occurs with a decrease in volume ( V < 0).
By Le Chatelier's principle, an increase in pressure shifts the equilibrium towards the side of smaller volume, i.e. towards water (ice melts).
dTmdP = T V Hfus < 0, the melting point of ice falls below 273.15 K at 2 atm.
At 2 atm and 273.15 K (constant temperature, now above the melting point), ice is not stable: the solid phase disappears completely and only water remains.
Volume of the system decreases, not increases.
Answer: (3)