Calculate the standard heat of formation of carbon disulphide (l). Given that the standard heats of combustion of carbon (s), sulphur (s) and carbon disulphide (l) are -393.3, -293.72 and -1108.76 kJ `mol^(-1)` respectively.

Options

A. `-128.02 kJ mol^(-1)`
B. `+12.802 kJ mol^(-1)`
C. `+128.02 kJ mol^(-1)`
D. `-12.802 kJ mol^(-1)`

Answer

C

Explanation

`C+ 2S rarr CS_(2) Delta H=` ?
`C + O_(2) rarr CO_(2) Delta H= -393.3kJ` ...(i)
`S + O_(2) rarr SO_(2) Delta H= -293.72kJ` ...(ii)
`CS_(2) + 3O_(2) rarr CO_(2) + 2SO_(2) Delta H= -1108.76 kJ` ...(iii)
eq (ii) `xx 2` + eq (i) - eq (iii) - and find required result