Chemistry S2 - Basic Stoichiometry Calculations

Stoichiometry

the calculation of the amounts of reactants & products involved in a chemical reaction

What is the representative particle for the element Na?

atom

What is the representative particle for the covalent compound H₂O?

molecule

What is the representative particle for the ionic compound NaOH?

formula unit

Mole Ratio

conversion factor that relates to amounts in moles of any 2 substances involved in chemical reaction

Stoichiometry Steps

1. write a balanced equation

2. identify the known (what is given in problem) and the unknown (what the problem is asking for)

3. ALWAYS start with known & include units

4. Identify & line up all needed conversion factors (mole ratio, molar mass, molar volume, Avogadro’s #)

5. calculate problem (recall what is on top is x & ÷ by what is on bottom)

6. check your answer (make sure units are cancelling)

Limiting Reactant

• the reactant completely used in chemical reaction

• determines amount of product(s) that can be produced

Excess Reactant

reactant that will have leftovers at the end of the reaction

Steps for Solving Limiting Reactant Problem (2 reactants)

1. make sure you have balanced equation

2. convert each reactant to moles if needed

3. pick 1 reactant & calculate amount of product you can make

4. pick other reactant & calculate amount of product you can make

5. one that makes least product is limiting reactant, other is excess reactant

6. use limiting reactant to determine amount product(s) can be produced & how much excess reactant will actually be consumed in reaction, rest is leftover

Percent Yield

• percent yield = actual yield/theoretical yield x 100

• a quick & simple way that scientists determine efficiency of chemical reaction

Actual Yield

actual amount that reaction actually produces

Theoretical Yield

amount that is expected from a reaction from the mole ratio