Chemical Reactions Review What is the difference between a What is the difference between a chemical and a physical reaction? chemical and a physical reaction?

Clues that a chemical reaction occurred: 1. Color change 2. Precipitate (Solid) formation 3. Bubble/gas formation 4. Heat/flame production or absorption.

In chemical reactions BONDS are BROKEN! BONDS are FORMED!

Chemical Equation Chemical Equation * Represents a chemical reaction * Represents a chemical reaction In the form: REACTANTS  PRODUCTS * In the form: REACTANTS  PRODUCTS * Physical states are given using symbols * Physical states are given using symbols Symbol State Symbol State (s) Solid (s) Solid (l) liquid (l) liquid (g) gas (g) gas (aq) aqueous(dissolved in water) (aq) aqueous(dissolved in water)

There are generally 5 types of reactions Synthesis Decomposition Single Replacement (displacement) Double Replacement (displacement) Double Replacement (displacement) Combustion Combustion

Synthesis Two or more simple substances combine to make a complex substance A + B  AB Example: solid magnesium and oxygen gas forming magnesium oxide 2 Mg (s) + O 2 (g)  2 MgO(s

Decomposition One complex substance is broken down into two or more simpler substances AB  A + B Example: Solid Mercury II oxide decomposes to solid mercury and oxygen gas 2 HgO(s)  2 Hg(s) + O 2 (g)

A single anion or cation is exchanged (a single element replaces an element in a compound) A + BC  B + AC or A + BC  BA + C Example: solid magnesium metal in aqueous hydrochloric acid (hydrogen monochloride) makes aqueous magnesium chloride and hydrogen gas Mg (s) + 2 HCl (aq)  MgCl 2 (aq) + H 2 (g) Single Replacement

Double Replacement The anions/cations are exchanged (an element from each of two compounds switch places) AB + CD  AD + CB Example: aqueous silver nitrate and aqueous sodium chloride react to make solid silver I chloride and aqueous sodium nitrate AgNO 3 (aq) +NaCl(aq)  AgCl(s) + NaNO 3 (aq) AgNO 3 (aq) +NaCl(aq)  AgCl(s) + NaNO 3 (aq)

Combustion A substance reacts with oxygen and releases A substance reacts with oxygen and releases light and heat in the process light and heat in the process X + O 2  XO or X + O 2  XO or (CH) x + O 2  CO 2 + H 2 O (CH) x + O 2  CO 2 + H 2 OExample: CH4 + 2 O 2  CO H 2 O CH4 + 2 O 2  CO H 2 O Methane gas is burned in air. It produces carbon dioxide and water.