Summary
Highlights
A mole ratio is the ratio between the numbers of moles of any two substances in a balanced chemical equation. The coefficients in a balanced equation represent these mole ratios. A mole is defined as 6.02 x 10^23 particles (atoms, ions, molecules, or formula units).
Using the reaction N2 + 3H2 → 2NH3, the coefficients mean one molecule of nitrogen reacts with three molecules of hydrogen to produce two molecules of ammonia. A model kit demonstrates the breaking of bonds in reactants and forming new bonds for products.
While coefficients can represent molecules, in practical chemistry, we work with moles because individual molecules are too small to measure by mass. Therefore, the coefficients represent mole ratios, allowing chemists to weigh quantities on a balance.
For the N2 + 3H2 → 2NH3 reaction, several mole ratios can be written: 1 mole N2 / 3 moles H2, 3 moles H2 / 1 mole N2, 1 mole N2 / 2 moles NH3, 2 moles NH3 / 1 mole N2, 3 moles H2 / 2 moles NH3, and 2 moles NH3 / 3 moles H2.
The practice problem uses the reaction 4Al + 3O2 → 2Al2O3. The possible mole ratios are: 4 moles Al / 3 moles O2, 3 moles O2 / 4 moles Al, 4 moles Al / 2 moles Al2O3, 2 moles Al2O3 / 4 moles Al, 3 moles O2 / 2 moles Al2O3, and 2 moles Al2O3 / 3 moles O2.
The coefficients in balanced equations are essentially mole ratios, and understanding them is crucial for calculations in chemistry. Mole ratios allow for the scaling of reactions from a molecular level to measurable quantities, enabling laboratory experiments.