Question

Given: ${ 2C(s) + 2O_2 (g) -> 2CO_2 (g) ; \Delta H = -787 kJ}$

• A. -1802 kJ
• B. #ERROR!
• C. #ERROR!
• D. -800 kJ

Answer 1

Answer: (C)

#ERROR!

Answer 2

$2 C (s)+2 O _{2}(g) \longrightarrow 2 CO _{2}(g) ;$ $\Delta H =-787 \,kJ \ldots (i)$ $H _{2}(g)+\frac{1}{2} O _{2}(g) \longrightarrow H _{2} O (l) ;$ $\Delta H =-286\, kJ \ldots (ii)$ $C _{2} H _{2}(g)+2 \frac{1}{2} O _{2}(g) \longrightarrow 2 CO _{2}(g)+ H _{2} O (l)$ $\Delta H=-1310 \,kJ \ldots (iii)$ Add the Eqs. (i) and (ii) and subtract E (iii) from them. $2 C + H _{2} \longrightarrow C _{2} H _{2}-787-286+1310$ $2 C + H _{2} \longrightarrow C _{2} H _{2}-1073+1310$ $2 C + H _{2} \longrightarrow C _{2} H _{2}+237$ Hence, the heat of formation of acetylene is + $237 \,kJ$.