1. Limiting Reactant:
* The limiting reactant is the reactant that is completely consumed in a chemical reaction.
* It sets an upper limit on how much product can be formed.
2. Excess Reactant:
* The excess reactant is the reactant that is not completely consumed in a chemical reaction.
* It has some amount left over after the reaction is complete.
3. The Stoichiometry of the Reaction:
* The balanced chemical equation for the reaction provides the stoichiometric ratios of reactants and products. This means it tells us the precise amounts of each substance involved in the reaction.
Here's how it works:
1. Imagine a recipe: You have a recipe for cookies that requires 2 cups of flour and 1 cup of sugar. If you only have 1 cup of flour, you can only make half the amount of cookies even if you have plenty of sugar. The flour is the limiting reactant.
2. The limiting reactant runs out first: In a chemical reaction, the limiting reactant gets used up completely before the other reactants. Once it's gone, the reaction stops.
3. No more product can be formed: Since the reaction stops when the limiting reactant is used up, no more product can be formed, even if there's excess of other reactants.
Example:
Let's say you have 10 grams of sodium (Na) and 10 grams of chlorine (Cl) reacting to form sodium chloride (NaCl):
```
2 Na + Cl2 → 2 NaCl
```
* Step 1: Calculate moles: Calculate the moles of each reactant using their molar masses.
* Step 2: Determine the limiting reactant: Compare the mole ratios of the reactants based on the stoichiometry of the reaction. The reactant with the lower mole ratio (relative to the coefficients in the balanced equation) is the limiting reactant.
* Step 3: Calculate the amount of product: The amount of product formed is determined by the amount of the limiting reactant consumed.
In summary: The limiting reactant controls the amount of product formed because it is the first to be fully consumed, thereby halting the reaction and preventing further product formation.
