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Chemical Reactions

Processes by which atoms of one or more substances rearrange to form new substance(s) (represented by chemical equations).


Evidence of Reactions

1. Temperature Change
• exothermic - energy released (hot)
• endothermic - energy absorbed (cold)

2. Change of State
• formation of precipitate - solid formed when two aqueous solutions react
• gas release (bubbling, effervescence)
• disappearance of a solid

3. Smell

4. Colour Change
• transparent, translucent, opaque

5. Other Energy Changes: Light, Sound, Electrical


Parts of Chemical Equations

• reactants (left side)
• products (right side)
• arrow symbol (yields or produces)
• state symbols (s, l, g, or aq subscripts)
• Stoichiometric coefficients


Types of Equations

1. Word Equation: Uses names of substances

2. Skeleton Equation: Uses formulas of substances (HOFBrINCl -g, g, g, l, s, g, g, are diatomic molecules with the subscript 2)

3. Balanced Equation: Uses coefficients in front of formulas to make atoms equal on both sides


Law of Conservation of Mass

In any chemical reaction, the mass of the reactant(s) is equal to the mass of the product(s) (balanced).



More than one reactant, one product formed.

A + B -> C

A and B are compounds or elements, C is always a compound.

Metal oxide (s) + Water (l) -> Metal Hydroxide (Base)

Nonmetal oxide (g) + Water (l) -> Acid



One reactant, more than one product formed.

A -> B + C

A is always a compound, B and C are compounds or elements.


Single Displacement (Cation Single Displacement)

An element on the Activity Series replaces another below it (ionic compound + element on Activity Series).

AX + B -> BX + A

If B is not higher than A on the Activity series, there is no reaction.


Single Displacement (Anion Single Displacement)

A halogen replaces another below it (ionic compound + halogen)

AX + Y -> AY + X


Double Displacement (Neutralization)

Two ionic compounds switch ions
Acid + Base -> Salt + Water
AX + BY -> BX + AY


Double Displacement (Gas Releasing Double Displacement)

An acid or base reacts with a salt to form an acid or base that decomposes into water and the corresponding gas.


Double Displacement (Precipitation)

A solid is formed when two aqueous solutions react
AX (aq) + BY (aq) -> BX + AY
Use solubility chart to predict precipitate (one must be solid or no reaction)