Chemical Reactions and Equations

CLASS NOTES

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!

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

reactionreactant1 + reactant2 products

• For example:hydrogen + oxygen water

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 CO₂Ca + O CaO

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

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)