Question

Which of the following compounds is NOT present in its standard state at 25\(^\circ\)C and 1 atmosphere pressure?

• A. \(\text{CO}_2(g)\)
• B. \(\text{CaCO}_3(s)\)
• C. \(\text{C}_2\text{H}_5\text{OH}(l)\)
• D. \(\text{H}_2\text{O}(g)\)

Hint:

Always remember that the standard state of water at 25\(^\circ\)C and 1 atm is \textbf{liquid}, not gas.

Answer 1

The Correct Option is D

Step 1: Understanding standard state.
The standard state of a substance is defined as its most stable physical form at 25\(^\circ\)C (298 K) and 1 atmosphere pressure.

Step 2: Evaluation of each option.
(A) \(\text{CO}_2(g)\): Carbon dioxide exists as a gas under standard conditions, so this is its standard state.
(B) \(\text{CaCO}_3(s)\): Calcium carbonate is a stable solid at room temperature and pressure, so this is its standard state.
(C) \(\text{C}_2\text{H}_5\text{OH}(l)\): Ethanol exists as a liquid at 25\(^\circ\)C, which is its standard state.
(D) \(\text{H}_2\text{O}(g)\): Water exists as a liquid at 25\(^\circ\)C and 1 atm. Therefore, water vapour is not its standard state.

Step 3: Conclusion.
Among the given options, \(\text{H}_2\text{O}(g)\) is not present in its standard state at 25\(^\circ\)C and 1 atm pressure.