Chemical Equations Notes
All chemical reactions have two parts:
 Reactants - the substances you start with
 Products- the substances you end up with (new substances
are formed)
Law of Conservation of Mass
Antoine Lavoisier – atoms cannot be created or destroyed
 All the atoms we start with we must end up with
 A balanced equation has the same number of each element
on both sides of the equation. Atoms are rearranged to
form new substances.
► How do I know I am writing my equations correctly?
Yields
 NaOH + HCl -------> H2O + NaCl
(Reactants) 1 Na 1 (Products)
1 O 1
2 H 2
1 Cl 1
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Which is the reactant? product?
Count the atoms on the reactant side.
Count the atoms on the product side.
Is it balanced?
To balance an equation, coefficients CAN be changed, but
subscripts CANNOT be changed.
Counting Atoms
► When you count atoms, remember to multiply the coefficient
number and the subscript number.
(Coefficient)
 2H2O

four atoms of hydrogen, two atoms of oxygen
2(NaOH)4
(Subscript)
eight atoms of sodium, eight atoms of oxygen, eight atoms of hydrogen
Physical Properties (review): color, shape, state of matter, shape, mass
Chemical Changes (examples): burning wood, frying and egg, rusting
metal, digesting food
Signs of a chemical change:
 Unexpected color change
 New odor
 Gas bubbles
 Light production
 An increase or decrease in temperature
(exothermic/endothermic)
 Precipitate (formation of a soid)