CHEM 121 Ch.4 Stoichiometry of Chemical Reactions

chemical equations

are concise representations of chemical reactions

where are reactants located in a chemical equation?

on the left

where are products located in a chemical equation?

on the right

subscripts

tell the number of atoms of each element in a molecule

coefficients

tell the number of molecules

balancing a chemical equation

1. find atoms that appears in the fewest times in the chemical formula

2. change the coefficients to have equal atoms on two sides

3. find the next one and change the coefficient

molecular equation

a way to represent a chemical reaction where all reactants and products are shown as complete, undissociated neutral compounds, regardless of whether they exist as individual molecules or as ions in a solution

identify the molecular equation

Pb(NO3)2(aq) + 2KI(aq) > PBIz(s) + 2KNO3(aq)

complete ionic equation

represents a chemical reaction by showing all dissolved ionic compounds and strong acids as their constituent, separated ions by an aqueous solution

net ionic equation

a chemical equation that shows only the chemical species that are actually involved in a chemical reaction, excluding spectator ions

how to write a net ionic equation

1. write a balanced molecular equation

2. dissociate the molecules into ions

3. identify and cancel spectator ions

precipitation reactions

reactions that result in the formation of an insoluble product (precipitate)

acids, bases, and neutralization reactions

H+ donor gives H+ to something that accepts it to form H2O

oxidation-reduction reactions

electrons are traded as evidenced by change in charge/oxidation number

soluble salt

can be written as NaCl(aq) or Na+(aq) + Cl-(aq)

slightly soluble salt

always written as AgCl(s)

soluble ionic compounds

• NH4+

• group 1 cations: Li+, Na+, Rb+, Cs+, K+

• Cl-, Br-, I-

• F-

• C2HO32-, HCO3-, NO3-, CIO3-

• SO42-

insoluble ionic compounds contain

• CO3-, CrO42-, PO43-, S2-

• OH-

how to predict whether a precipitate forms

1. note ions present in the reaction

2. consider the possible cation-anion combinations

3. use solubility rule to determine if any of the combinations are insoluble