In chemistry, the "ratio of an equation" typically refers to the mole ratio derived from the coefficients of a balanced chemical equation. This ratio is crucial for understanding the quantitative relationships between reactants and products.
What is the Mole Ratio?
The mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a balanced chemical reaction. It is determined by the coefficients that appear before the formulas of these substances in the balanced equation.
How to Find the Mole Ratio
To find the mole ratio from a chemical equation, follow these steps:
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Ensure the Equation is Balanced: The chemical equation must be balanced. This means the number of atoms of each element on the reactant side is equal to the number of atoms of that same element on the product side. If it's not balanced, you must balance it first.
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Identify Coefficients: Locate the numerical coefficients in front of each chemical formula in the balanced equation. These coefficients represent the relative number of moles (or molecules/atoms) of each substance involved in the reaction.
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Form the Ratio: To find the mole ratio between any two substances (let's call them Substance A and Substance B) in the equation, simply form a fraction using their coefficients:
$\text{Mole Ratio} = \frac{\text{Coefficient of Substance A}}{\text{Coefficient of Substance B}}$ or $\frac{\text{Coefficient of Substance B}}{\text{Coefficient of Substance A}}$
As highlighted in the provided reference (0:14 - 8:43 in the YouTube video), "If you have moles of one substance. And the coefficients from the balanced equation you can use the ratio to figure out moles of the other compounds." This underscores the practical application of the mole ratio.
Example: The Haber Process
Consider the balanced equation for the synthesis of ammonia (the Haber Process):
$\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)$
Here are some mole ratios you can find from this equation:
| Substances | Coefficients | Mole Ratio |
|---|---|---|
| $\text{N}_2$ to $\text{H}_2$ | 1 and 3 | $\frac{1 \text{ mol N}_2}{3 \text{ mol H}_2}$ or $\frac{3 \text{ mol H}_2}{1 \text{ mol N}_2}$ |
| $\text{N}_2$ to $\text{NH}_3$ | 1 and 2 | $\frac{1 \text{ mol N}_2}{2 \text{ mol NH}_3}$ or $\frac{2 \text{ mol NH}_3}{1 \text{ mol N}_2}$ |
| $\text{H}_2$ to $\text{NH}_3$ | 3 and 2 | $\frac{3 \text{ mol H}_2}{2 \text{ mol NH}_3}$ or $\frac{2 \text{ mol NH}_3}{3 \text{ mol H}_2}$ |
These ratios can be used in stoichiometry calculations. For instance, if you have 5 moles of $\text{N}_2$, you can use the ratio $\frac{2 \text{ mol NH}_3}{1 \text{ mol N}_2}$ to calculate the moles of $\text{NH}_3$ that can be produced.
Why are Mole Ratios Important?
Mole ratios are fundamental in stoichiometry because they allow chemists to:
- Predict the amount of product formed from a given amount of reactant.
- Determine the amount of reactant needed to produce a specific amount of product.
- Calculate the amount of one reactant needed to react completely with another reactant.
In essence, the mole ratio is the key bridge between the amounts of different substances in a chemical reaction, derived directly from the balanced equation's coefficients.
