Question

Calculate the standard heat of formation of carbon-di-sulphide(l). Given that the standard heats of combustion of carbon(s), sulphur(s) & carbon disulphide(l) are -393.3, -293.7 & -1108.76 $kJmo{l}^{-1}$ respectively.

• A. 228.02 kJ
• B. -128.02 kJ
• C. 128.02 kJ
• D. -228.02 kJ

Answer 1

The correct option is C

128.02 kJ

Given equations are: $C\left(s\right)+O_2\left(g\right)\to C{O}_2\left(g\right)△H=-393.3kJ------\left(i\right)$

$S\left(s\right)+O_2\left(g\right)\to S{O}_2\left(g\right)△H=-293.72KJ------\left(ii\right)$

$C{S}_2+3O_2\left(g\right)\to C{O}_2\left(g\right)+2S{O}_2\left(g\right)△H=-1108.76kJ------\left(iii\right)$

Multiply the equation (ii) by 2

$2S\left(s\right)+2O_2\left(g\right)\to 2S{O}_2\left(g\right)△H=-587.44kJ------\left(iv\right)$

Add equatios (i) & (iv) and subtracting equation (iii) we get

$C\left(s\right)+2S\left(s\right)\to C{S}_2\left(l\right)$

$\therefore △H_f=-393.3-587.44+1108.76$ $△H_f=128.02kJ$