Chemistry 11 : Limited Reactants

The limiting reactant

-   In many experiments, have the amounts of multiple reactants. o   Which amount do you use to calculate the amount of products? o   The amount you could use is the amount of limiting reactant o   The limiting reactant is the reactant that limits the amount of product produced o   The limiting reactant is the completely used up at the end of the reaction -   All other reactants are excess reactants there will be more reactants left over at the of the reaction Example 2g of hydrogen gas and 12g of oxygen gas are put into a vessel and reacted in the reaction

2H2(g) + O2(g) -> 2 H2O(g)

What is the limiting reactant? mH2O = 2.00g H2 * 1g /2.02gH2 * 2molH2o/2mol H2 *18.02gH2o/1mol =  17.8g mH2 = 1.01 g* 2 = 2.02g/mol mH2O = 18.02g/mol

If O2 is the LR

mH2O = 12.0g O2 * 1mol O2/32.00g O2 * 2OH2O/1molO = 18.00g/1mol=  13.5g mO2 = 32.00g

Oxygen is the limiting reactant (13.5g < 17.8g)

Finding the LR in this way also tells us the amount of the product is produced

Finding the excess reactant Find the LR Use the amount of the LR to find how much of the excess reactant actually reacted Subtract the amount that actually reacted from the given amount

Example How much of mass of    the excess reactant remained after the reaction completed?

mH2 = 12.0g O2* 1mol O2/32gO2 * 2mol H2/1mol O2 * 9.02H2/1mol H2 = 1.52g