Question

Which of the following processes is an endothermic ?

• A. The aqueous NaOH and HCl solutions mixed together.
• B. Formation of ammonia by Haber process.
• C. Ice melts at room temperature.
• D. The freezing of liquid water.

Hint:

An endothermic process absorbs heat from the surroundings.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
An endothermic process absorbs heat from the surroundings, so \(\Delta H\) is positive. An exothermic process releases heat.

Step 2: Check option (A):
Mixing aqueous NaOH and HCl is neutralisation, which releases about 57 kJ per mole of water formed. It is exothermic.

Step 3: Check option (B):
Formation of ammonia by the Haber process, \(\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3\), has \(\Delta H = -92\) kJ. It is exothermic.

Step 4: Check options (C) and (D):
Ice melting needs heat to break hydrogen bonds in the solid (fusion), so it is endothermic. Freezing of water is the reverse and releases heat, so it is exothermic.

Final Answer:
Only melting of ice absorbs heat, so option (C) is correct. \[ \boxed{\text{(C) Ice melts at room temperature}} \]