How much energy is released when 6 moles of octane is burnt in air- Given Hf- for CO2 g- H2Og and C8H18 l respectively are -490- -240 and -160 J-mol

The correct option is C 35.5 kJ C + O_2 = CO_2 H = 490 .... (i) H_2 + 12 O_2 = C_8 H_18 H = 240 ...... (ii) 8C + 9H_2 = C_8 H_18 H = +16 ...

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Standard XII

Chemistry

Hess' Law

How much ener...

Question

How much energy is released when $6 m o l e s$ of octane is burnt in air? Given $△ H_{f}^{\circ}$ for $C O_{2} (g), H_{2} O (g)$ and $C_{8} H_{18} (l)$ respectively are $- 490, - 240$ and $+ 160 J / m o l$

- 6.2 k J

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- 37.4 k J

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- 35.5 k J

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- 20.0 k J

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Solution

The correct option is C $- 35.5 k J$
$C + O_{2} = C O_{2} △ H = - 490 . . . . (i)$
$H_{2} + \frac{1}{2} O_{2} = C_{8} H_{18} △ H = - 240 . . . . . . (i i)$
$8 C + 9 H_{2} = C_{8} H_{18} △ H = + 160 . . . . . . (i i i)$
$2 C_{8} H_{18} + 25 O_{2} = 16 C O_{2} + 18 H_{2} O$
The required reaction can be obtained by
$2 \times (i i i) - 16 (i) - 18 (i i)$
$16 C + 18 H_{2} - 16 C - 16 O_{2} - 18 H_{2} - 9 O_{2}$
$= 2 C_{8} H_{18} - 16 C O_{2} - 18 H_{2} O$
or $- 25 O_{2} = 2 C_{8} H_{18} - 16 C O_{2} - 18 H_{2} O$
$2 C_{8} H_{18} + 25 O_{2} = 16 C O_{2} + 18 H_{2} O$
$[△ H = 2 \times 160 - 16 \times - 490 - 18 \times - 240]$
$△ H = - 11840 J = - 11840 k J$ for $2 m o l e s$ of octane. Energy released for $6 m o l e s$ of octane $= - 11.840 \times 3 = - 35.5 k J$ .
Hence, option C is correct

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Similar questions

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How much energy is released when 6 moles of octane is burnt in air? Given △H∘f for CO2(g),H2O(g) and C8H18(l) respectively are −490,−240 and +160 J/mol

How much energy is released when $6 m o l e s$ of octane is burnt in air? Given $△ H_{f}^{\circ}$ for $C O_{2} (g), H_{2} O (g)$ and $C_{8} H_{18} (l)$ respectively are $- 490, - 240$ and $+ 160 J / m o l$