Combustion of a Hydrocarbon
Complete combustion of a hydrocarbon in oxygen, releasing energy and producing carbon dioxide and water.
Formula
Variables
Example
Methane: CH₄ + 2O₂ → CO₂ + 2H₂O
How it works
This equation shows the complete combustion of a hydrocarbon, meaning every carbon atom ends up as carbon dioxide and every pair of hydrogen atoms ends up as water. The coefficients come from balancing atoms: x carbons require x CO2 molecules, y hydrogens require y/2 H2O molecules, and the oxygen needed is then counted from the products, giving x + y/4 O2 molecules. It only applies when oxygen is plentiful enough for complete burning, so no carbon monoxide or soot is formed.
When to use it
Use this formula when balancing reactions for fuels such as alkanes, or when calculating how much oxygen is needed for full combustion. It is also useful for finding the amounts of CO2 and H2O produced from burning a known hydrocarbon sample.
Worked example, step by step
Example: complete combustion of propane, C3H8 Step 1: Identify x and y. C3H8 means x = 3 and y = 8. Step 2: Find the oxygen coefficient. x + y/4 = 3 + 8/4 = 3 + 2 = 5 Step 3: Write the balanced equation. C3H8 + 5O2 → 3CO2 + 4H2O Step 4: Check atoms. Left: C = 3, H = 8, O = 10 Right: C = 3, H = 8, O = 10 So the equation is balanced.
Common mistakes to avoid
- Forgetting that oxygen must be balanced after carbon and hydrogen are matched
- Using the wrong water coefficient and writing y H2O instead of y/2 H2O
- Applying the formula to incomplete combustion, where CO or soot may form instead of only CO2 and H2O
Did You Know?
Incomplete combustion (too little oxygen) produces carbon monoxide and soot instead of clean CO₂ and water.
Share this formula
More in Chemistry
View allIdeal Gas Law
IntermediateRelates pressure, volume, moles and temperature of a gas.
Molarity
BasicConcentration in moles of solute per litre of solution.
Moles from Mass
BasicNumber of moles from mass and molar mass.
pH
BasicAcidity from hydrogen-ion concentration.
pOH
BasicBasicity from hydroxide-ion concentration.
Henderson–Hasselbalch
AdvancedpH of a buffer solution.