Question

Octane C8H18 is burnt in excess oxygen to give CO2 and water. -5 pts Enthalpy of reaction _C8H18 (1) + O2( → _ _CO2 (g) + _ _ H2O(g) AH = - 10, 922kJ/mol Rxn 1) Is the reaction exothermic or endothermic 2) 2) Balance the reaction. 3) Calculate the energy change when 1 .0L of octane ( d= 0.69g/ml) is burnt in excess oxygen

Answer 1

(1) $\Delta$ H = -10,922 kJ/mol Rxn

Since $\Delta$ H is negative, therefore, heat is released by the reaction.

Hence, this reaction is exothermic.

(2) The balanced reaction is :

2 C₈H₁₈ (l) + 25 O₂ (g) $\rightarrow$ 16 CO₂ (g) + 18 H₂O (g)

(3) volume of octane = 1.0 L = 1000 mL

mass of octane = (volume of octane) * (density octane)

mass of octane = (1000 mL) * (0.69 g/mL)

mass of octane = 690 g

moles octane = (mass of octane) / (molar mass octane)

moles octane = (690 g) / (114.23 g/mol)

moles octane = 6.04 mol

energy change = (moles octane) * ($\Delta$H)

energy change = (6.04 mol C₈H₁₈) * (-10922 kJ / 2 mol C₈H₁₈)

energy change = -(6.04 * 10922 / 2) kJ

energy change = -32986.9 kJ