Introduction to Chemical Reactions

Chemistry 20Miss Nicklas

IntroductionO All chemical reactions (simple or

complex) involved changes in substancesO One or more starting substances are

changed into one or more new substances

O Reactants Products

Introduction, cont.O Remember: in a chemical reaction,

atoms are NOT created or destroyed, they are just rearrangedO Bonds are broken and new bonds are

formedO We are going to study 5 types of

chemical reactionsO Our knowledge of these will help us to

predict what will happen

Writing Chemical Equations

O This is a way of describing chemical reactions

O Word EquationO magnesium + oxygen magnesium

oxideO Skeleton Equation

O Mg (s) + O2 (g) MgO (s)

O Balanced EquationO 2 Mg + O2 2 MgO

ExamplesO 1. Write a skeleton equation for this

chemical reaction:O When calcium carbonate is heated,

calcium oxide and carbon dioxide are produced

O CaCO3 (s) heat CaO (s) + CO2

ExamplesO 2. Write a sentence that completely

describes the chemical reaction shown in the equation:

O NaHCO3 (s)+ HCl (aq) NaCl (aq) + H2O (l) + CO2 (g)

O When sodium carbonate is reacted with hydrochloric acid, sodium chloride, water, and carbon dioxide are produced

Diatomic MoleculesO Notice: many non-metallic elements

exist as covalently bonded moleculesO Molecules that share electrons

O There are 7 elements that form diatomic molecules (molecules made of 2 atoms)O H2,O2, N2, F2, Cl2, Br2, I2