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Question
Heat of combustion of C(s), H2(g) and C2H6(g) are −x1, −x2 and −x3 respectively. Hence heat of formation of C2H6(g) is ____________.
Options
−X3 + 2x1 + 3x2
−x1 − x2 + x3
x1 + x2 − x3
−2x1 − 3x2 + x3
MCQ
Fill in the Blanks
Solution
Heat of combustion of C(s), H2(g) and C2H6(g) are −x1, −x2 and −x3 respectively. Hence heat of formation of C2H6(g) is −2x1 − 3x2 + x3.
Explanation:
\[\ce{C + O2 -> CO2}\], ΔH1 = −x1 .........(i)
\[\ce{H2 + 1/2O2 -> H2O}\], ΔH2 = −x2 ......(ii)
\[\ce{C2H6 + 7/2O2 -> 2CO2 + 3H2O}\], ΔH3 = −x3 ..........(iii)
Multiply equation (i) by 2 + multiply equation (ii) by 3 − equation (iii)
∴ \[\ce{2C + 3H2 -> C2H6}\]
∴ ΔH = 2ΔH1 + 3ΔH2 − ΔH3
∴ ΔH = −2x1 − 3x2 + x3
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Spontaneous (Irreversible) Process
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