A city of 100,000 people uses approximately 1.0 * 10¹¹ kJ of energy per day. Suppose all of that energy comes from the combustion of liquid octane (C₈H₁₈) to form gaseous water and gaseous carbon dioxide. Use standard enthalpies of formation to calculate ΔH°_rxn for the combustion of octane and then determine the number of kilograms of octane necessary to provide this amount of energy.

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SORT You are given the amount of energy used and asked to find the mass of octane required to produce the energy. STRATEGIZE The conceptual plan has three parts. In the first part, write a balanced equation for the combustion of octane. In the second part, calculate AHin from the AH's of the reactants and products. In the third part, convert from kilojoules of energy to moles of octane using the conver- sion factor found in step 2, and then convert from moles of octane to mass of octane using the molar mass. GIVEN: 1.0 x 10¹¹ kJ FIND: kg C8H18 CONCEPTUAL PLAN (1) Write the balanced equation. (2) (3) AHx AHi's AHxn npAH (products) - Σn,AH; (reactants) kJ mol C8H18 114.22 g C8H18 mol CH18 Conversion factor to be determined from steps 1 and 2 RELATIONSHIPS USED molar mass C8H18 = 114.22 g/mol 1 kg = 1000 g g C8H18 1 kg 1000 g kg C8H18