Chemistry U8 - Reactions, Equations

Chemical change

NEW SUBSTANCE FORMS w/ chemical properties which differ from og substance

EX: rusting, oxidizing

Physical change

DOES NOT CHANGE IDENTITY of substance

EX: evaporation, melting, subliming

Chemical reaction

Process by which 1 OR MORE substances change into 1 OR MORE NEW SUBSTANCES

Caused by: CHANGE IN CHEM BONDS (electrons)

“new substances = new chem properties”

Exothermic

(REACTION) energy is RELEASED as a PRODUCT

EX: CH4 + O4 → CO2 + H2O

Endothermic

(REACTION) energy is ABSORBED as a REACTANT

EX: N2O4 + energy → NO2

Chemical equation

Shows formulas and relative amounts of all reactants and products

“Reactants yields Products”

Subscript

Small number on bottom right of ELEMENT, multiples to specific element or polyatomic ion it’s attached to

EX: in H2O, subscript is 2

Coefficient

Large number before FORMULA, multiplies the entire substance it’s next to

EX: 6O2, coefficient is 6

Word equations

CONTAINS NAMES

EX: carbon dioxide and water are PRODUCED when methane gas reacts with oxygen.

Methane + Oxygen → Carbon dioxide + Water

Atom Inventories

Counts number of EACH KIND OF ATOM on BOTH SIDES OF EQUATION.

• Count # with multiplying subscripts on elements, subscripts outside parenthesis containing elements and Coefficient

• SAME # OF EACH ATOM ON BOTH SIDES = BALENCED

law of conservation of matter

“Matter cannot be created or destroyed”

Diatomic Molecules

H2, O2, N2, F2, CL2, Br2, I2

(Brin-cl-hof), mnemonic or H + 7 on PT

Combustion

Oxidation reduction of organic compound, HEAT IS RELEASED

Reacts W/ OXYGEN TO MAKE CO2 AND H20

**Typically includes Even REACTANT and Odd PRODUCT

EX: CH4 + 2O2 → CO2 + 2H2O

Synthesis

Two or More substances react to form a new compound

2 OR MORE REACTANTS, ONLY 1 PRODUCT

EX: 2C + 2O → 2CO

Decomposition

Single compound breaks down to form 2 or More SIMPLER COMPOUNDS

1 REACTANT MORE THAN 1 PRODUCT

EX: 2H2O → 2H2 + O2

Single displacement

“Home-wrecker reaction” Single element reacts w/ compound and TAKES PLACE of ONE OTHER ELEMENT IN COMPOUND

**Element + compound form into element + compound

EX: 2Al (s) + CuCl2 (aq) → AlCl3 (aq) + 3Cu (s)

Double displacement

Gas, solid, precipitate, or a molecular compound forms from the apparent EXCHANGE OF ATOMS or ions between TWO COMPOUNDS

**2 Compounds make 2 DIFFERENT compounds

EX: 2KI (aq) + Pb(NO3)2 → PbI2 (s) + 2KNO3 (aq)