The heating value of combustible fuels is evaluated based on thequantities known as the higher heating value (HHV) and the lowerheating value (LHV). The HHV has a higher absolute value and isobtained by assuming that the water formed in the combustionreaction is formed in the liquid state. The LHV has a lowerabsolute value and is obtained by assuming that the water formed inthe combustion reaction is formed in the gaseous state. The LHV istherefore the sum of the HHV (which is negative) and the heat ofvaporization of water for the number of moles of water formed inthe reaction (which is positive). The table below lists theenthalpy of combustion (which is equivalent to the HHV) for severalclosely related hydrocarbons. Use the information in the table toanswer the following questions.
| Alkane | ΔHcombΔHcomb
(kJ/molkJ/mol) |
| CH4(g)CH4(g) | −−890. |
| C2H6(g)C2H6(g) | −−1560 |
| C3H8(g)C3H8(g) | −−2219 |
| C4H10(g)C4H10(g) | −−2877 |
| C5H12(l)C5H12(l) | −−3509 |
| C6H14(l)C6H14(l) | −−4163 |
| C7H16(l)C7H16(l) | −−4817 |
| C8H18(l)C8H18(l) | −−5470 |
Part A
Given the provided data, complete and balance the combustionequation for the combustion of butane, CH3CH2CH2CH3CH3CH2CH2CH3,using whole-number coefficients for CO2CO2 and H2OH2O, assumingliquid water forms:
CH3CH2CH2CH3(g)+O2(g)→     –––+      –––CH3CH2CH2CH3(g)+O2(g)→     _+      _
Express your answer as a balanced chemical equation using thesmallest whole-number coefficients including phases.
View Available Hint(s)
Part B
The following table lists heat of formation values for selectcompounds:
| Compound | ΔH∘fΔHf∘
(kJ/molkJ/mol) | | Compound | ΔH∘fΔHf∘
(kJ/molkJ/mol) |
| CO2(g)CO2(g) | −−393.5 | C4H10(g)C4H10(g) | −−125.7 |
| H2O(g)H2O(g) | −−241.8 | C5H12(g)C5H12(g) | −−146.9 |
| CH4(g)CH4(g) | −−74.6 | C6H14(g)C6H14(g) | −−167.4 |
| C2H6(g)C2H6(g) | −−84.68 | C7H16(g)C7H16(g) | −−187.9 |
| C3H8(g)C3H8(g) | −−103.85 | C8H18(g)C8H18(g) | −−208.7 |
Part C
Calculate ΔHΔH for the combustion of one mole of butane gas,C4H10C4H10, assuming H2O(l)H2O(l) is produced instead ofH2O(g)H2O(g).
Express the change in enthalpy in kilojoules to five significantfigures.
Part D
Calculate ΔHΔH for the combustion of one mole of butane gas,C4H10C4H10, assuming H2O(g)H2O(g) is produced instead ofH2O(l)H2O(l).
Express the change in enthalpy in kilojoules to five significantfigures.
| | |
| ΔHcombΔHcomb when H2O(g)H2O(g) is produced = | nothing | kJkJ |
