The mole ratio of oxygen (O₂) to carbon dioxide (CO₂) in the complete combustion reaction for propane (C₃H₈) is 5:3. This means that for every 5 moles of oxygen consumed, 3 moles of carbon dioxide are produced.
Understanding Mole Ratios in Chemical Reactions
A mole ratio is a fundamental concept in stoichiometry, representing the exact proportions in which reactants combine and products are formed in a balanced chemical equation. It provides a direct numerical relationship between the amounts of any two substances involved in a reaction. For instance, in the combustion of propane, a 5:3 mole ratio between oxygen and carbon dioxide signifies that you need 5 moles of oxygen to produce 3 moles of carbon dioxide.
The Combustion of Propane: A Balanced Perspective
The combustion of propane is a chemical reaction where propane (C₃H₈) reacts with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O). To determine the accurate mole ratios, the chemical equation must first be balanced.
The balanced chemical equation for the complete combustion of propane is:
C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)
From this balanced equation, we can directly observe the stoichiometric coefficients, which represent the mole ratios of the reactants and products:
- 1 mole of propane (C₃H₈)
- 5 moles of oxygen (O₂)
- 3 moles of carbon dioxide (CO₂)
- 4 moles of water (H₂O)
Therefore, the mole ratio of oxygen to carbon dioxide is precisely 5:3.
How to Determine Mole Ratios: Balancing the Equation
Determining mole ratios hinges on having a correctly balanced chemical equation. Here's how the propane combustion equation is balanced:
-
Write the Unbalanced Equation:
C₃H₈ + O₂ → CO₂ + H₂O -
Balance Carbon Atoms:
There are 3 carbon atoms on the left (in C₃H₈). Place a coefficient of 3 in front of CO₂ on the right to balance carbon.
C₃H₈ + O₂ → 3CO₂ + H₂O -
Balance Hydrogen Atoms:
There are 8 hydrogen atoms on the left (in C₃H₈). Place a coefficient of 4 in front of H₂O on the right to balance hydrogen (4 × 2 = 8).
C₃H₈ + O₂ → 3CO₂ + 4H₂O -
Balance Oxygen Atoms:
Count the total oxygen atoms on the right side: (3 × 2) from CO₂ + (4 × 1) from H₂O = 6 + 4 = 10 oxygen atoms.
To balance, place a coefficient of 5 in front of O₂ on the left side (5 × 2 = 10).
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
The equation is now balanced, and the coefficients reveal the mole ratios. For more on balancing chemical equations, you can refer to resources like Khan Academy's guide on balancing chemical equations.
Significance in Chemistry and Practical Applications
Mole ratios are indispensable tools in chemistry for several reasons:
- Stoichiometric Calculations: They allow chemists to predict the exact amount of reactants needed or products formed in a chemical reaction. For example, if you know the amount of propane you want to burn, you can calculate precisely how much oxygen is required and how much carbon dioxide will be produced.
- Limiting Reactant Determination: Mole ratios help identify the limiting reactant, which is the reactant that will be completely consumed first, thereby stopping the reaction and limiting the amount of product formed.
- Industrial Processes: In industrial settings, understanding mole ratios is crucial for optimizing chemical reactions, minimizing waste, and ensuring efficient production of desired compounds.
Here's a summary of the mole ratios in the complete combustion of propane:
| Reactant/Product | Chemical Formula | Moles (Coefficient) |
|---|---|---|
| Propane | C₃H₈ | 1 |
| Oxygen | O₂ | 5 |
| Carbon Dioxide | CO₂ | 3 |
| Water | H₂O | 4 |
From this table, the ratio of Oxygen (O₂) to Carbon Dioxide (CO₂) is clearly 5:3.
