Stoichiometry is that area of chemistry which deals with the quantitative relationships between reactants and products in a chemical rxn and between atoms in a compound.

Background

Avogadro's Number: 6.022 X 10²³

1 mole of a substance contains 6.022 X 10²³ particles.(learn!)

1 mole of sodium, Na, contains6.022 X 10²³ atoms and weighs 22.99 g.

The atomic weight of Na is 22.99 g/mol.

The atomic weight of an element is ______________________________.

The molecular weight of a substance is ________________________________

__________________________________________.

ClF₃ (assume we have one mole)

How many moles of Cl?

How many moles of F?

Formula weight is used for ionic cpds (metal + nonmetal(s))

Ca(NO₃)₂

(see board)

Chemical Equations

CH₄ + 2O₂ --> CO₂ + 2H₂O

reactants --> products

Law of conservation of mass implies that there should be the same no. of atoms of each type on both sides of the equation. When the coefficients in the eq. show this, the eq. is said to be balanced.

A balanced eq. shows __________________________________________________________

_____________________________________________________________

Balancing Chemical Equations

General Approach:

1. Write down unbalanced equation.

2. Balance each element one at a time. Start with the most complicated molecule or with an element that appears only once on each side of the equation. Balance pure elements last (e.g., O₂, P₄, S₈, Cu)

(examples)

Stoichiometric Calculations

Balanced equation gives relative numbers of moles of reactants and products.

N₂(g) + 3H₂(g) --> 2NH₃(g)

General Approach for Calculating Masses of Reactants and Products:

1. Balance the eq. for the rxn.

2. Convert known masses of substances to ___________.

3. Use balanced equation to determine _______________ which give the necessary conversion factors, e.g.,

1 mol N₂ = 2 mol NH₃

4. Use these conversion factors to find __________ of reactant or product.

5. Convert moles to grams if necessary.

(examples)

Limiting Reactant (or reagant): The reactant which is used up first when a reaction is carried out. The limiting reactant limits and therefore determines the amount of product which can be formed.

(see board)

Efficiency of Reactions

% yield =

actual yield = amount of product actually obtained

theoretical yield = expected amount of product which would be obtained if the reaction went to completion according to the balanced eq. & if no product were lost.

(see board)