Question
When carbon is burnt in a definite amount of oxygen, the product will be CO, if excess amount of carbon is present and the product will be CO2 if excess amount of O2 is present. The enthalpies of formation of CO(g) and CO2(g) are −75 and −95 kcal/mol, respectively. In which of the following case, the amount of heat evolved will be maximum?
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Solution
$(a)\underset{\begin{aligned} & \\ & (9.0) \end{aligned}}{C} + \underset{(4.5)}{\frac{1}{2}O_{2}} \rightarrow CO;\Delta H = - 75\text{ kcal}$
Heat evolved = 75 × 9 = 675 kcal
$(b)C + O_{2} \rightarrow CO_{2};\Delta H = - 95\text{ kcal} $$$22$$
Heat evolved = 95 × 2 = 190 kcal
$(c)4C + 3.5O_{2} \rightarrow CO + 3CO_{2}$
Heat evolved = 75 × 1 + 95 × 3 = 360 kcal
$(d)C + O_{2} \rightarrow CO_{2};\Delta H = - 95\text{ kcal} $$$2.52.5$$
Heat evolved = 95 × 2.5 = 237.5 kcal
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