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Question
Calculate the standard enthalpy of the reaction:
SiO2(s) + 3C(graphite) → SiC(s) + 2CO(g) from the following reactions:
- Si(s) + O2(g) → SiO2(s), ΔrH° = −911kJ
- 2C(graphite) + O2(g) → 2CO(g), ΔrH° = −221kJ
- Si(s) + C(graphite) → SiC(s), ΔrH° = −65.3kJ
Solution
Reverse the Eq. (i)
(i) SiO2(s) → Si(s) + O2(g), ΔrH° = −911kJ
Add equations (ii), (iii) and (iv)
(ii) 2C(graphite) + O2(g) → 2CO(g), ΔrH° = −221kJ
(iii) Si(s) + C(graphite) → SiC(s), ΔrH° = −65.3kJ
(iv) SiO2(s) → Si(s) + O2(g), ΔrH° = +911kJ
________________________________________________
SiO2(s) + 3C(graphite) → SiC(s) + 2 CO(g), ΔrH° = +624kJ.
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