Chemical thermodynamics

Hess's law

Exercise 4

Using these data: (a) $H_2(g)$ $+$ $\frac{1}{2}O_2(g)$ $\longrightarrow$ $H_2O(l)$ $\Delta H_a$ $ = $ $-285.8 kJ$ (b) $N_2O_5(g)$ $+$ $H_2O(l)$ $\longrightarrow$ $2HNO_3(l)$ $\Delta H_b$ $ =$ $ -76.6 kJ$ (c) $\frac{1}{2}N_2(g)$ $+$ $\frac{3}{2}O_2(g)$ $ +$ $\frac{1}{2}H_2(g)$ $\longrightarrow$ $HNO_3(l)$ $\Delta H_c$ $ = $ $-174.1 kJ$ calculate the standard enthalpy of the following reaction: (d) $2N_2(g)$ $+$ $5O_2(g)$ $\longrightarrow$ $2N_2O_5(g)$ $\Delta H_d = ?$

-2(a) $2H_2O(l)$ $\longrightarrow$ $2H_2(g)$ $+$ $O_2(g)$ $-2\Delta H_a$ -2(b) $4HNO_3(l)$ $\longrightarrow$ $2N_2O_5(g)$ $+$ $2H_2O(l)$ $-2\Delta H_b$ 4(c) $2N_2(g)$ $+$ $6O_2(g)$ $+$ $2H_2(g)$ $\longrightarrow$ $4HNO_3(l)$ $4\Delta H_c$

-2(a)-(b)+4(c) $2H_2O(l)$ $+$ $4HNO_3(l)$ $+$ $2N_2(g)$ $+$ $6O_2(g)$ $ +$ $2H_2(g)$ $\longrightarrow$ $2H_2(g)$ $+$ $O_2(g)$ $+$ $2N_2O_5(g)$ $+$ $2H_2O(l)$ $+$ $4HNO_3(l)$ $-2\Delta H_a$ $-$ $2\Delta H_b$ $+$ $4\Delta H_c$ (d)= -2(a)-(b) $2N_2(g)$ $+$ $5O_2(g)$ $\longrightarrow$ $2N_2O_5(g)$ $\Delta H_d$ $=$ $-2\Delta H_a$ $-$ $2\Delta H_b$ $+$ $4\Delta H_c$ $=$ $28.4kJ$