Question

Identify the equation in which change in enthalpy is equal to change in internal energy

• A. $2H_2{O}_2(I)\to 2H_{2}O(I)+O_2(g)$
• B. $C(s)+O_2(g)\to C{O}_2(g)$
• C. $PC{l}_5(g)\to PC{l}_3(g)+C{l}_2(g)$
• D. $N_2(g)+3H_2(g)\to 2N{H}_3(g)$

Answer 1

Answer: (B)

Key Idea Relationship between change in enthalpy and change in intemal energy is given as:

$\Delta H=\Delta U+\Delta n_{g}RT$

In the given options,

(a) $2H_2{O}_2(l)\to 2H_{2}O(l)+O_2(g)$ $\Delta n_g=1$

$\therefore \Delta H=\Delta U+RT$

(b) $C(s)+O_2(g)\to C{O}_2(g)$

$\Delta n_g=1-1=0$

$\therefore \Delta H=\Delta U$

(c) $PC{l}_5(g)\to PC{l}_3(g)+C{l}_2(g)$

$\Delta n_g=2-1=1$

$\therefore \Delta H=\Delta U+RT$

(d) $N_2(g)+3H_2(g)\to 2N{H}_3(g)$

$\Delta n_{g}RT=2-3=-1$

$\therefore \Delta H=\Delta U-RT$

Equation given in option (b) has enthalpy change equal to internal change