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Question
The energy released when 6 moles of octane is burnt in air will be: [Given, △Hf for CO2(g),H2O(g) and C8H18(l), respectively are −490,−240 and +160 J/mol].
The energy released when 6 moles of octane is burnt in air will be: [Given, △Hf for CO2(g),H2O(g) and C8H18(l), respectively are −490,−240 and +160 J/mol].
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Solution
The correct option is D −35.5 kJ
C+O2→CO2;△H=−490 J......(i)
H2+12O2→H2O;△H=−240 J.....(ii)
8C+9H2→C8H18;△H=+160 J.....(iii)
On applying, 8x Eq. (i) +9x Eq. (ii) - Eq. (iii), we get
C8H18+252O2→8CO2+9H2O
△H0R=[8×(−490)]+[9×(−240)]+160
=−5920 J mol−1
Hence, energy exchange when 6 moles of octane is burnt in air =−5920×6 =−35520 J =−35.5 kJ.
C+O2→CO2;△H=−490 J......(i)
H2+12O2→H2O;△H=−240 J.....(ii)
8C+9H2→C8H18;△H=+160 J.....(iii)
On applying, 8x Eq. (i) +9x Eq. (ii) - Eq. (iii), we get
C8H18+252O2→8CO2+9H2O
△H0R=[8×(−490)]+[9×(−240)]+160
=−5920 J mol−1
Hence, energy exchange when 6 moles of octane is burnt in air =−5920×6
=−35520 J
=−35.5 kJ.
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