Question

In which of the following changes at constant pressure is work done by system on surrounding?

	Initial state		Final state
(i)	$H_{2}O\left(g\right)$	$\to$	$H_{2}O\left(l\right)$
(ii)	$H_{2}O\left(s\right)$	$\to$	$H_{2}O\left(g\right)$
(iii)	$H_{2}O\left(l\right)$	$\to$	$H_{2}O\left(s\right)$
(iv)	$3H_2\left(g\right)+N_2\left(g\right)$	$\to$	$2N{H}_3\left(g\right)$
(v)	$CaC{O}_3\left(s\right)$	$\to$	$CaO+C{O}_2\left(g\right)$

• A. i
• B. ii
• C. iii
• D. iv
• E. v

Answer 1

Answer: (B), (E)

The correct options are
B ii
E v

Work done= $-P\left(\Delta V\right)$

For work done by system on surroundings, $W$= negative

$\therefore \Delta V$ should be positive.

$\Delta V$ is positive when the system moves to a higher active state i.e., from solid to liquid, solid to gas or liquid to gas.

Therefore, option (B) and (E) are correct answers.