The reaction of cyanamide, `NH_(4)CN(s)`, with dioxygen was carried out in a bomb calorimeter, and `DeltaU` was found to be -742.7 kJ `mol^(-1)` at 298 K. calculate the enthalpy change for the reaction at 298 K.
`NH_(4)CN(g)+(3)/(2)O_(2)(g) to N_(2)(g)+CO_(2)(g)+H_(2)O(l)`

Options

A. `-741.46" kJ "mol^(-1)`
B. `741.46" kJ "mol^(-1)`
C. `241.46 " kJ "mol^(-1)`
D. `-241.6" kJ "mol^(-1)`

Answer

A

Explanation

`NH_(4)CN(s)+(3)/(2)O_(2)(g) to N_(2)(g)+CO_(2)(g)+H_(2)O(l)`
`Deltan_(g)=n_(p)-n_(r)=2-(3)/(2)=(1)/(2)=0.5`
`DeltaH=DeltaU+Deltan_(g)RT`
`DeltaH=-742.7" kJ "mol^(-1)`
`+(0.5xx8.314xx10^(-3)" kJ "mol^(-1)xx298K)`
`=-743.7+1238.786xx10^(-3)`
`=741.46" kJ "mol^(-1)`