The enthalpy change for chemical reaction is denoted as `DeltaH^(Theta)` and `DeltaH^(Theta) = H_(P)^(Theta) - H_(R)^(Theta)`. The relation between enthalpy and internal enegry is expressed by equation:
`DeltaH = DeltaU +DeltanRT`
where `DeltaU =` change in internal enegry `Deltan =` change in number of moles, `R =` gas constant.
For the change, `C_("diamond") rarr C_("graphite"), DeltaH =- 1.89 kJ`, if `6g` of diamond and `6g` of graphite are seperately burnt to yield `CO_(2)` the heat liberated in first case is

Options

A. Less than in the second case by `1.89 kJ`
B. Less than in the second case by `11.34 kJ`
C. Less than in the second case by `14.34 kJ`
D. More than in the second case by `0.945 kJ`

Explanation

`C(g) +O_(2) rarr CO_(2)(g), DeltaH =- y …(i)`
`C(d) rarr C(g), DeltaH =- 1.89 kJ …(ii)`
Adding equations (i) and (ii), we get
`C(g) +C(d) +O_(2) rarr CO_(2) +C(g), DeltaH =- y +1.89 kJ`
or `C(d) +O_(2) rarr CO_(2), DeltaH =- y +1.89 kJ`
Hence, teh combustion of diamond releases enegry less than `1.89 kJ`.