unit 4: chemical reactions and stoichiometry

physical change

change to appearance without changing identity (intermolecular forces are broken and new ones are formed; crush, boil, melt)

chemical change

change that transforms one substance into a different substance (chemical bonds are broken and new ones are formed; burning, decomposing)

chemical reactions

represented through chemical equations.

1. save elements that appear in multiple products/reactants for last (usually O or H)

2. keep conserved polyatomic ions together

3. balance 1 element at a time

   a. the number and type of atoms remain the same, but their arrangement changes when going through a reaction

molecular equation

ionic compounds always expressed as neutral compounds

complete ionic equation

the ions of aqueous compounds are written out individually (keep solids, liquids, and gases together)

net ionic equation

like complete ionic equation, but removes spectator ions that don’t react (aqueous compounds on both sides are removed)

limiting reactant

determines how much product you can make based on the quantities of reactants

combination (synthesis) reaction

A + B → AB

decomposition reaction

AB → A + B

single-replacement reaction

AB + C → AC + B

double-replacement reaction

AB + CD → AD + BC

(generally) nonreactive metals

copper, silver, mercury, platinum, and gold generally don’t like being in a compound, and often react to become a solid metal

bronsted-lowry acid

acids “donate” a hydrogen ion (proton) to bases

1. HCl + NaOH → NaCl + H2O

bronsted-lowry base

bases accept a hydrogen ion (proton) from acids

conjugate acid

results when a base accepts a proton

conjugate base

results when an acid donates its proton

amphoteric molecules

can act as either an acid or base (H2O, HCO3-, etc.)

redox (oxidation-reduction) reaction

a reaction where electrons are transferred between 2 substances (electrons tracked using oxidation numbers)