Mol Ratios

Mol Ratios

Balanced Equations show ratios usually in terms of moles. 

2Al₂O₃ ---> 4Al + 3O₂

(For every 2 moles of Al₂O₃ that is used, 4 moles of Al and 3 moles of O₂ are produced)

Mole-Mole Problems:

The quantity of one or more reactants is given in moles. The quantity of products in moles is requested. The mole ratio is used to calculate.

Excess and Limiting Reactants:

If reactants are not combined in their mol ratio, one will run out and the other will be excess. The one that runs out is called the limiting reactant. The limiting reactant (or limiting reagent) in a chemical reaction is the substance that is totally consumed when the chemical reaction is complete. The amount of product formed is limited by this reagent as the reaction can not continue. 

To determine the limiting reactant:

1. Convert both the given masses (grams) to amounts in moles
2. Then calculate the number of moles of one of the products
3. The reactant yielding the smaller number of moles of product is the limiting reactant

Percent Yield

% yield = actual yield/theoretical yield x 100%

• Theoretical Yield: is the maximum amount of the product that can be produced from a given amount of reactant
• Actual Yield: The measured amount of a product from a reaction