Calculate the standard enthalpy of the reaction,
`SiO_2(s) + 3C ("graphite") to SiC (s) + 2CO(g)` from the following reactions,
i. `Si(s) + O_2(g) to SiO_2(s), Delta_rH^0 = -911 kJ`
ii. `2C ("graphite") + O_2(g) to 2CO(g), Delta_rH^0 = - 221 kJ`
iii. `Si(s) + C ("graphite") to SiC(s), Delta_rH^0 = - 65.3kJ`

Explanation

Reverse the Eq. (i)
iv. `SiO_2(s) to Si(s) + O_2(g), Delta_rH^0 = -911 kJ`
Add equations (ii), (iii) and (iv)
ii. `2C("graphite") +O_2(g) to 2CO(g), Delta_rH^0 = - 221 kJ`
iii.`Si(s) + C("graphite") to SiC(s), Delta_rH^0 = -65.3 kJ`