Question

3. Fossil fuels (petroleum, natural gas, and coal) are excellent fuels composed primarily of hydrocarbons, which when burned in an adequate supply of air are oxidized, forming carbon dioxide and water. Chemical bonds are broken and new bonds are formed, and as a result, energy is released as heat. Calculate the following in the spaces provided using the table below. Show all work.

Hydrocarbon	Heat of Combustion (kJ/g)	Molar Heat of Combustion (kJ/mol)
Methane	55.6	890
Ethane	52	1560
Propane	50.0	2260
Butane	49.3	2859
Pentane	48.8	3510
Hexane	48.2	4151
Hepne	48.2	4817
Octane	47.8	5450
Decane	47.2	6760

Write a balanced chemical equation that includes a quantity of thermal energy for the complete combustion of the following alkanes:

Propane

Butane

Octane

Decane

Answer 1

Hi balancing chemical equation is a trial and error method work, please be familiar or you may take help from online resources or any software for this purpose. Remember always first balance carbons only otherwise it will become more hardwork and tedious.

1. Propane Combustion equation:

C₃H₈ (g) + 5O₂ (g) → 3CO₂ + 4H₂O  (g) ΔH = -2260 kJ/mol

2. Butane Combustion equation:

C₄H₁₀ (g) + O₂ (g) → 4CO₂ (g) + 5H₂O (g)   ΔH = -2859 kJ/mol

3. Octane Combustion equation:

2 C₈H₁₈ (g) + 25 O₂ (g) → 16 CO₂ (g) +18 H₂O (g) ΔH = -5450 kJ/mol

4. Decane Combustion equation:

2 C₁₀H₂₂ (g) + 31 O₂ (g) → 20 CO₂ (g) + 22 H₂O (g)         ΔH = -6760 kJ/mol

NOTE: All ΔH values have a negative sign before the energy value, it represents an exothermic reaction (Thermal enrgy released).

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