Chemical Equations Chemistry Mrs. Coyle

Chemical Equations: represent chemical reactions Word Equations Skeleton Chemical Equations Balanced Chemical Equations

Reactants  Products Methane + Oxygen  Carbon Dioxide + Water The arrow (yield sign) and indicates that a reaction took place. Word Equations: show the names of the reactants and the products

Skeleton Chemical Equations The formulas of the reactants and products are written without indicating their relative amounts. Example: CH 4 + O 2  CO 2 +H 2 O

Balanced Chemical Equations The chemical formulas and the relative amounts of the reactants and products are written. Example: CH 4 + 2O 2  CO 2 + 2H 2 O The coefficients indicate the relative amounts of each substance. Equal number of atoms of each element must appear on both sides of the balanced equation.

Why does a chemical reaction have to be balanced? In any chemical or physical change, mass is neither created or destroyed Mass is CONSTANT Law of Conservation of Mass (Antoine Lavoisier)

Combustion of Methane CH 4 + 2O 2  CO 2 + 2H 2 O Atoms are rearranged!

Example: Decomposition of hydrogen peroxide in the presence of a catalyst. Word equation: hydrogen peroxide  water + oxygen

Example: Decomposition of hydrogen peroxide in the presence of a catalyst. Skeleton equation: H 2 O 2  H 2 O + O 2

Example: Decomposition of hydrogen peroxide in the presence of a catalyst. Balanced Equation: 2H 2 O 2  2H 2 O + O 2

Example: Decomposition of hydrogen peroxide in the presence of a catalyst. Balanced equation showing the catalyst (MnO 2 ) the state of the reactants and products: MnO 2 2H 2 O 2 ( l )  2H 2 O ( l ) + O 2 ( g )