Chapter 5

Stoichiometry and

Chemical Equations

Chemical Compounds

• Remember compounds can be either ionic or molecular– Ionic compounds are formed between a cation

and an anion• These ions can be monatomic or polyatomic

– Molecular compounds are formed between two or more nonmetals of similar electronegativities.

– Don’t forget acids (H+ and some anion)

Writing chemical formulas

• When writing chemical formulas, listen to the name.– If you hear prefixes, the compound is

molecular (no charges, no flipping)– For all other compounds, you need to find

charges and then flip the charges• Memorize ions and charges

Naming chemical compounds

• Look at the beginning species…– If it is a nonmetal, then the compound is

molecular…use the prefixes in the name– If it is a metal, then the compound is ionic…

know which metals need roman numerals– If it is ammonium, just name it

Balancing chemical equations

Moles

• There are three definitions for the mole– 1 mole equals the mass of the substance in

grams.– 1 mole contains Avogadro’s number of

particles (6.022 × 1023)– 1 mole of a gas @ STP occupies 22.4 L

Mole diagram

Simple idea about moles

• Look at the following formula– C12H22O11

• In one mole of sucrose, there are 12 moles of C, 22 moles of H, and 11 moles of O

• In 10 moles of sucrose, there are 120 moles of C, 220 moles of H, and 110 moles of O

• In 5 moles of sucrose, there are 60 moles of C, 110 moles of H, and 55 moles of O

Moles and Gases

• Remember the Ideal Gas Law

PV = nRT• You can rearrange the formula in order to

solve for the number of moles.– Remember that R must have the same units

as the pressure unit

% Composition

Empirical Formulas

• Steps for solving problems1. Determine moles of each element

2. Do the mole ratio (divide each mole answer by the smallest mole number…looking for a whole number…double all if you get a half a whole number)

3. The whole numbers become the subscripts in the formula.

Stoichiometry…The Box

Limiting vs Excess

Who is limiting?

• In order to determine which reactant is limiting and which reactant is in excess, you must compare moles.

• Whichever reactant runs out first is the limiting reactant.– This is the reactant that must be used to

determine how much product is made.

Molarity and Molality

• Molarity is moles of solute divided by liters of solution (notice…total volume of soln)

• Molality is moles of solute divided by kg of solvent (notice solvent only)

• Therefore we can find moles by…

moles = Molarity × vol (L)

moles = Molality × kg

For test, know….

• How to balance

• Mole conversions

• % composition

• # moles of element when looking at formula

• Empirical formula (by calculation & thinking)

• Limiting vs excess….product formed