Chapter 7 Types of Reactions Types of Reactions

Chapter 7 Types of Reactions

Types of Reactions �Synthesis �Decomposition �Single-replacement �Double-replacement �Combustion

Reaction Classification �Reactions are classified based on the: �Type of reactant �Number of reactants �Number of products

Synthesis Reactions � 2+ substances react to form a single substance �The reactants may be single elements or compounds �The product is always a compound �A + B → AB

Synthesis Reactions �Examples: � 2 Na + Cl 2 → 2 Na. Cl (table salt) �Sodium reacts with chlorine to form sodium chloride. � 2 H 2 + O 2 → 2 H 2 O (water) �Hydrogen reacts with oxygen to form dihydrogen monoxide or water.

Decomposition Reactions �The opposite of synthesis reactions �A compound breaks down into 2+ simpler substances. �The reactant must be a compound. �The products may be single elements or compounds. �AB → A + B

Decomposition Reactions �Examples: � 2 H 2 O → 2 H 2 + O 2 �Water breaks down into hydrogen and oxygen. �Ca. CO 3 → Ca. O + CO 2 �Calcium carbonate breaks down into calcium oxide and carbon dioxide.

Single Replacement Reactions � 1 element takes the place of another element in a compound �A + BC → B + AC

Single Replacement Reactions �Examples: �Cu + 2 Ag. NO 3 → 2 Ag + Cu(NO 3)2 �Copper reacts with silver (I) nitrate and replaces silver to form copper (II) nitrate and silver. � 2 K + 2 H 2 O → H 2 + 2 KOH �Potassium reacts with dihydrogen monoxide and replaces a hydrogen to produce potassium hydroxide and hydrogen.

Double Replacement Reactions � 2 different compounds exchange positive ions and form 2 new compounds �AB + CD → AD + CB

Double Replacement Reactions �Examples: �Pb(NO 3)2 + 2 KI → Pb. I 2 + 2 KNO 3 �Lead (II) nitrate reacts with potassium iodide to form lead (II) iodide and potassium nitrate. �Ca. CO 3 + 2 HCl → Ca. Cl 2 + H 2 CO 3 �Calcium carbonate reacts with hydrogen monochloride to form calcium chloride and dihydrogen carbonate.

Combustion Reactions �A substance reacts rapidly with oxygen �Often heat and light are produced �This is what happens when gas is burned to power cars or fireplaces or Bunsen burners.

Combustion Reactions �Examples: �CH 4 + 2 O 2 → CO 2 + 2 H 2 O + heat �Carbon tetrahydride or methane reacts with oxygen to produce carbon dioxide, water, and heat. � 2 H 2 + O 2 → 2 H 2 O �This can also be called a synthesis reaction. Sometimes classifications can overlap. �Hydrogen reacts with oxygen to produce water and heat.

Questions! What type of reaction is it if: 1. Oxygen is a reactant? 2. 2 reactants form 1 product? 3. 1 reactant forms 2 products? 4. Both the reactants and products contain 2 compounds? 5. Both the reactants and products contain 1 compound and 1 single element?

Answers! 1. 2. 3. 4. 5. Combustion Synthesis Decomposition Double replacement Single replacement

Oxidation-Reduction Reactions �Electrons are transferred from 1 reactant to another �Also called redox reactions �This was the last reaction discovered because it is based on subatomic particle (electron) transfer that was not originally known about.

Oxidation �Any process in which an element loses electrons during a chemical reaction. �A reactant is oxidized if it loses electrons. �Originally scientists thought that oxygen had to be present for this to happen. Now we know that several elements are capable of taking electrons.

Oxidation �Examples: � 2 Ca + O 2 → 2 Ca. O �Calcium loses electrons to oxygen and forms calcium oxide. �Na + Cl → Na. Cl �Sodium loses electrons to chlorine and forms sodium chloride.

Reduction �The process in which an element gains electrons during a chemical reaction. �A reactant is said to be reduced if it gains electrons. �Oxidation and reduction ALWAYS occur together because when 1 element loses electrons the other element gains them.