1. Chemical Reactions and Equations CLASS NOTES

2. Review from last class What types of changes can occur as a result of chemical reactions? – Can you give an example? – Physical changes! – Chemical changes!

3. What is involved in a chemical reaction? There are two parts to a chemical reaction: – Reactants and Products Reactants are those substances you begin with Products are the substances formed by the reaction reactant1 + reactant2  products For example: hydrogen + oxygen  water

4. Chemical equations Chemical reactions are written using equations, with reactants on one side and products on the other: Word equations! e.g. sodium + chlorine  sodium chloride carbon + oxygen  carbon dioxide calcium + oxygen  calcium oxide Usually written with chemical formulas (symbols): Ex. Na + Cl  NaCl C + O₂  CO₂ Ca + O  CaO

5. Chemical equations continued… The number of atoms on one side of the chemical equation is equal to the other side: Reactant1 + reactant 2  product  is the same as equals, or produces

6. Endothermic and Exothermic Reactions In a chemical reaction, bonds in the reactants break and new bonds form in the products Breaking and creating bonds requires energy Two types of chemical reactions: – Absorbs energy = endothermic (energy in = ENtrance) – Releases energy = exothermic (energy EXits)