Question

Which from following reactions performs zero work?

• A. \(\text{CH}_{4(\text{g})} + \text{Cl}_{2(\text{g})} \longrightarrow \text{CH}_3\text{Cl}_{(\text{g})} + \text{HCl}_{(\text{g})}\)
• B. \(3\text{H}_{2(\text{g})} + \text{N}_{2(\text{g})} \longrightarrow 2\text{NH}_{3(\text{g})}\)
• C. \(\text{C}_2\text{H}_{2(\text{g})} + \frac{5}{2}\text{O}_{2(\text{g})} \longrightarrow 2\text{CO}_{2(\text{g})} + \text{H}_2\text{O}_{(\text{l})}\)
• D. \(2\text{C}_2\text{H}_{6(\text{g})} + 7\text{O}_{2(\text{g})} \longrightarrow 4\text{CO}_{2(\text{g})} + 6\text{H}_2\text{O}_{(\text{l})}\)

Hint:

If \(\Delta n_g = 0\), work done = 0.

Answer 1

The Correct Option is A

Concept:
Work depends on change in moles of gaseous species: \[ w \propto \Delta n_g \] Step 1: Check gaseous moles in option (A). Reactants = 2 moles gas Products = 2 moles gas \[ \Delta n_g = 0 \]
Step 2: Conclusion. No change in volume → no work done.