Chapter 8A Chemical Equations and Reactions West Valley High School General Chemistry Mr. Mata

Standard 3a Students will know how to describe chemical reactions by writing properly balanced equations.

Essential Question Describe the 5 different types of chemical reactions that are in chemistry.

Chemical Reactions Products and Reactants Write compounds to react on left and compounds produced on the right. Remember, reactants react to produce products Read as “yields”

Symbols and Notation (l) – compound is a liquid (s) – compound is a solid (l) – compound is a liquid (g) – compound is a gas (aq) – aqueous (dissolved in water, exists as ions) ↓ - a precipitate has formed (solid falling out of the reaction) ↑ - a gas is evolved (bubbling out of the reaction) Various things can be put over the “yields” sign (→) to indicate special conditions.

Reaction Types Composition or Synthesis Decomposition Combustion There are five basic reaction types: Composition or Synthesis two or more reactants produce a single product. Decomposition a single reactant breaks down into its parts. Combustion rxn between oxygen and a reactant:

Reaction Types Single Displacement or Single Replacement One ion kicks one of the ions in the pair out. Double Displacement or Double Replacement Ion pairs switch places (partners). You must have a positive ion-negative ion pair in each position. Never a + to + or a – to - .

Chemical Equations Chemical reaction expressed with chemical equation. Shows relative number of products and reactants required to satisfy the Law of Conservation of Mass. Our lab reaction: Must be written: This balances the equation (reactants = products).

Rules for Balancing Chemical Rxns Never Change Subscripts Balance Groups First Balance H2O, O2, and H2 last. We balance by adding coefficients. Two reactant oxygens Four product hydrogens Properly balanced 2 2

Mole Ratios Mole ratios: how many moles of products are produced with given number of moles of reactants. Here, the mole ratio is 1:1:2 (1H2 : 1Cl2 : 2 HCl) This means two moles of HCl will be produced when one mole of H2 and one mole of Cl2 react.

Balancing Practice 4 3 2 2 2 2 5 4 2 6 6 6 + Energy + Energy + Energy Balance the following reactions on your own: 4 3 2 Rust 2 2 Thermite + Energy 2 5 4 2 + Energy Acetylene torch 6 6 6 + Energy Respiration