Question

What is the value of critical temperature of water?

• A. 647 K
• B. 312 K
• C. 346 K
• D. 493 K

Hint:

Water has exceptionally high critical constants ($T_c = 647\ \mathrm{K}$ and $P_c = 218\ \mathrm{atm}$) compared to other common small molecules like $\mathrm{CO_2}$ or $\mathrm{NH_3}$ because its extensive intermolecular hydrogen-bonding network requires an immense amount of energy to destabilize.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the standard experimental value of the critical temperature ($T_c$) of water ($\mathrm{H_2O}$) expressed on the Kelvin absolute temperature scale.

Step 2: Key Formula or Approach:
The critical temperature of a substance is the precise threshold temperature above which it cannot exist as a stable liquid phase, regardless of how much external pressure is applied. Gas molecules above this thermal state possess too much kinetic energy for intermolecular attractions to bind them into a liquid form.

Step 3: Detailed Explanation:
For water ($\mathrm{H_2O}$), the strong intermolecular hydrogen bonding network requires significant thermal energy to be disrupted up to the critical point. Experimentally, the critical temperature of water is measured to be $374^{\circ}\mathrm{C}$. To convert this Celsius value to the absolute Kelvin scale, add 273.15: $$T_c = 374 + 273.15 = 647.15\ \mathrm{K} \approx 647\ \mathrm{K}$$ Looking at the options provided, this maps directly to $647\ \mathrm{K}$.

Step 4: Final Answer:
The critical temperature of water is 647 K, which matches option (A).