Please show all steps. Solution The equations to be used here are: C5H12 + 8O2 -

Question

Explanation / Answer

The equations to be used here are: C5H12 + 8O2 --> 5CO2 + 6H2O The enthalpy change here is the heat of combustion of pentane, which is given in your information above as 3536 kJ per mole. Also, to form 5CO2 and 6H2O from the constituent elements in their standard states, we would need 5 x (-393.5) + 6 x (-285.8) kJ, or -3682.3 kJ. Hence we can use Hess' Law to find out the enthalpy change of formation of pentane. Hess' Law states that the enthalpy change of a reaction is dependent on the reactants and products, and is independent of the pathway taken between these reactants and products. Hence, we have the equations: 5C + 6H2 + 8O2 --> 5CO2 + 6H2O (-3682.3 kJ) C5H12 + 5O2 --> 5CO2 + 6H2O (-3536 kJ) Taking the first equation backwards, we have 5CO2 + 6H2O --> 5C + 6H2 + 8O2 (+3682.3 kJ) Hence we have an overall equation: C5H12 + 5O2 --> 5CO2 + 6H2O --> 5C + 6H2 + 8O2 This overall equation, taken backwards (after discounting the intermediate CO2 and H2O) is the enthalpy change of formation. Thus, to calculate, we take negative of the first arrow (3536 kJ) plus negative of the second arrow (-3682.3 kJ). Hence, the enthalpy change of formation is -146.3 kJ. Hope I was of help!

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.