14.1 Chemical Reactions ANNE - 1: start at 7; 2: done; 3: start at 6; 4: done

Chemical Reactions Chemical reaction: the process of breaking chemical bonds and reforming new bonds to make new substances

Evidence of Chemical Change Four indicators of a chemical change: 1. Formation of new gas 2. Formation of new solid 3. Release of energy (heat or light) 4. Color change

Reactants and Products Reactant: starting substance(s) Product: new substance(s) formed

Reaction Symbols arrow = “to produce” The small symbols in the parentheses (s, l, g, aq) indicate the phase of each substance in the reaction. Symbol Meaning (s) solid (l) liquid (g) gas (aq) aqueous - dissolved in solution

Law of Conservation of Mass Mass of reactants = mass of products

A Reminder: Numbers in Chemical Formulas

Balancing Chemical Equations The law of conservation of mass tells us that atoms and molecules must be balanced on both sides of a chemical equation.

Balancing Chemical Equations coefficient subscript Rules: Subscripts (small numbers) CANNOT be changed. Coefficients (big numbers) can be placed in front of the chemical formula. A coefficient applies to ALL atoms in the chemical formula. Multiply coefficients by subscripts to get the total atoms.

Balancing Chemical Equations Example #1 ___Cu2S + ___ O2 → ___ Cu2O + ___ SO2

Balancing Chemical Equations Example #2 ___ Al + ___ O2 → ___ Al2O3

Balancing Chemical Equations EXIT SLIP ___ CO2 + ___ H2 → ___ CH4 + ___ H2O