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Question
Calculate the standard enthalpy of the reaction, \[\ce{SiO2_{(s)} + 3C_{(graphite)} -> SiC_{(s)} + 2CO_{(g)}}\] from the following reactions:
- \[\ce{Si_{(s)} + O2_{(g)} -> SiO2_{(s)}}\], ΔrH0 = −911 kJ
- \[\ce{2C_{(graphite)} + O2_{(g)} -> 2CO_{(g)}}\], ΔrH0 = −221 kJ
- \[\ce{Si_{(s)} + C_{(graphite)} -> SiC_{(s)}}\], ΔrH0 = −65.3 kJ
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Solution
Reverse the Eq. (i)
(iv) \[\ce{SiO2_{(s)} -> Si_{(s)} + O2_{(g)}}\], ΔrH0 = −911 kJ
Add equations (ii), (iii) and (iv)
(ii) \[\ce{2C_{(graphite)} + O2_{(g)} -> 2CO_{(g)}}\], ΔrH0 = −221 kJ
(iii) \[\ce{Si_{(s)} + C_{(graphite)} -> SiC_{(s)}}\], ΔrH0 = −65.3 kJ
(iv) \[\ce{SiO2_{(s)} -> Si_{(s)} + O2_{(g)}}\], ΔrH0 = −911 kJ
________________________________________________
\[\ce{SiO2_{(s)} + 3C_{(graphite)} → SiC_{(s)} + 2 CO_{(g)}}\], ΔrH0 = +624 kJ
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