First slide

Hess law of constant summation

Question

How much energy is released when 6 mole of octane is burnt in ? Given $∆ H_{f}^{0}$ for CO_2(g), H₂O_(g) and C₈H_18(l) respectively are -390, -240 and +160 KJ/mol

Moderate

Solution

$\begin{array}{l} {C_{18}}{H_{18}}(l) + \frac{{25}}{2}{O_2}(g) \to 8C{O_2}(g) + 9{H_2}O(l)\\ \Delta {H_C} = [8\Delta {H_f}(C{O_2}) + 9\Delta {H_f}({H_2}O)] - [\Delta {H_f}({C_8}{H_{18}}) + \frac{{25}}{2}\Delta {H_f}({O_2})]\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\, = 8( - 390) + 9( - 240) - (160 + 0)\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = - 3120 - 2160 - 160 = - 5440KJ/mole \end{array}$

when 1 mole is burnt energy released = 5440KJ
for 6 moles energy released = ?
                                        = 6 x 5440 = 32,640KJ
                                        = 32,640 x 10^-3 MJ
                                          = 32.64MJ

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App