Question

How many kJ of heat are released when 2.5 g of octane undergo complete combustion according to the reaction:$$C_8H_{18} + 12.5 O_2 \rightarrow 8 CO_2 + 9 H_2O$$Given: Enthalpy of combustion of octane = -5,470 kJ/mol.

Answer 1

First, we need to determine the number of moles of octane  C8H18  in 2.5 g. The molar mass of octane is:C: 12.01 g/mol * 8 = 96.08 g/molH: 1.01 g/mol * 18 = 18.18 g/molMolar mass of octane = 96.08 + 18.18 = 114.26 g/molNow, we can find the number of moles of octane in 2.5 g:moles of octane = mass / molar mass = 2.5 g / 114.26 g/mol = 0.02186 molThe enthalpy of combustion of octane is given as -5,470 kJ/mol. To find the amount of heat released during the combustion of 0.02186 mol of octane, we can use the following equation:Heat released = moles of octane * enthalpy of combustion per moleHeat released = 0.02186 mol *  -5,470 kJ/mol  = -119.6 kJTherefore, 119.6 kJ of heat are released when 2.5 g of octane undergo complete combustion.