1. Chemistry I Honors Northwestern High School Jeff Venables
Chemical Reactions
Chemistry I Honors
Northwestern High School
Jeff Venables

2. Chemical Equations Reactants → Products
Reactants – the starting materials in a chemical reaction
Products – the ending materials in a chemical reaction
What happens during a chemical reaction?

3. Evidence of a chemical reaction:
Color Change
Heat Change
Solid Forms (precipitate)
Gas Forms (bubbles)

4. Symbols used in Chemical Equations
+ separates two reactants or two products
→ “yields” – separates reactants from products
(s), (l), (g), (aq) – states of substances
indicates heat is added
indicates a catalyst is used

5. Balancing Chemical Equations
Law of Conservation of mass
In a chemical reaction, atoms are “rearranged.”
There must be the same number of atoms of each element on each side of the equation (reactants and products)
Count atoms, then change coefficients, if necessary, to balance the equation.

6. 2 H2 (g) + O2 (g) → 2 H2O
Subscripts
(cannot be changed)
Coefficients

7. Examples – Balance the following equations
KClO3 → KCl + O2
N2 + H2 → NH3
Ca3(PO4)2 + NaOH → Na3PO4 + Ca(OH)2
K + H2O  KOH + H2

8. Examples – Balance the following equations
2KClO3  2KCl + 3O2
N2 + 3H2  2NH3
Ca3(PO4)2 + 6NaOH  2Na3PO4 + 3Ca(OH)2
2K + 2H2O  2KOH + H2