Question

The standard heat of formation of carbon disulphide $\left(l\right)$ given that standard heat of combustion of carbon (s), sulphur (s) and carbon disulphide $\left(l\right)$ are -393.3, -293.72 and -1108.76 KJ mol${}^{-1}$ respectively is

• A. -12.502 KJ. mol${}^{-1}$
• B. +128.02 KJ.mol${}^{-1}$
• C. -128.02 KJ.mol${}^{-1}$
• D. +12.802 KJ.mol${}^{-1}$

Answer 1

Answer: (B)

+128.02 KJ.mol${}^{-1}$

(i) $C\left(s\right)+O_2\to C{O}_2\left(g\right)$
(ii) $S\left(s\right)+O_2\to S{O}_2\left(g\right)$
(iii) $C{S}_2+3O_2\to C{O}_2+2S{O}_2$

(i) + 2 x (ii) - (iii) gives
$C\left(s\right)+2S\left(s\right)\to C{S}_2\left(l\right)$
$\Delta H=-$393.2 + 2 (-293.72) + 1108.76
$=$ + 128.02 KJ mol ${}^{-1}$