Chemical Reactions Notes

Combustion reactions, rules on balancing equations, reaction types, and symbols

Br I N Cl H O F

Br I N Cl H O F

These are diatomic atoms. When written alone, they must be in a pair. EX: O2

Law of Conservation of Mass and Energy

Mass and energy is neither created or destroyed in an ordinary chemical reaction.

Products come _____ the reactants.

after

Exothermic

A reaction that releases energy (and heat).

Endothermic

A reaction that absorbs energy (and heat).

+

Separates 2 or more reactants or products

→

“Yield,” separates reactants from products. Does not mean “equal to.”

<-->

Used in place of ⇌ to indicate a reversable reaction.

(s)

Designates a reactant or product in the solid state. Placed after the formula. EX: NaCl(s)

(↓)

Alternative to (s), but only used for a solid PRODUCT, not reactants. Indicates a precipitate.

(l)

Indicates a liquid reactant or product.

(aq)

Indicates an aqueous solution (where some solute has been dissolved in water).

(g)

Indicates a gaseous reactant or product.

(↑)

Alternative to (g), but ONLY for a gaseous PRODUCT.

△→

Triangle above arrow Indicates heat was supplied in the reaction.

Pt→

A formula written above or below the sign indicates that it is used as a catalyst (something that speeds up the reaction).

Subscript

Small numbers within a formula of a compound. Tells the number of atoms in that compound.

Coefficient

The large number in front of the formula or compound. Tells the number of molecules (in a molecular compound), formula units (in an ionic compound), or atoms of an element.

Synthesis

(Combination) Where 2 or more elements or compounds combine to form ONE complex substance. Only ONE PRODUCT.

Decompostion

A compound decomposes into 2 or more simple substances. Heat or electricity usually required. Only one reactant.

Single-Replacement

Occurs when one element displaces another element in a compound. You must check the Activity Series

Double-Replacement

Occurs when the cations (positive ions) “switch” places. You will need solubility rules to predict if the reaction occurs.

Combustion

Where oxygen reacts with another substance, a hydrocarbon or alcohol, resulting in the release of energy, usually heat or light. Carbon dioxide and water are the only two products.