Chemistry Lesson # 7 Types of Reactions

1. Synthesis A synthesis reaction is the combination of small atoms/molecules into larger molecules. It is also called a combination reaction. General Formula: A + B → AB When there is only ONE product, you can tell it is synthesis. Visuals: heat or light given off as the reactants come together Real-Life Examples: metals burning in oxygen to form a coating called an oxide (iron oxide is rust), sulfur compounds reacting with water to form acid rain (sulfuric acid)

Synthesis (continued) Example: 2 H2 + O2 → 2 H2O Example: H2O + CO2 → H2CO3 *Note that although synthesis reactions can involve elements or compounds, metals or non-metals, the only ones you will have to predict the products for will be between a metal and a non-metal. In this case, they create an ionic compound.

Practice Sodium + Chlorine → Magnesium + Phosphorus →

2. Decomposition A decomposition reaction is the splitting of a large molecule into elements or smaller molecules. General Formula: AB → A + B When only ONE reactant exists, it must be decomposition. Visuals: Usually these reactions involve heat, pressure, or a catalyst to force the reaction to occur, and if a gas is one of the products, you may see the gas being given off. Real-Life Examples: Breaking apart water or methane (CH4) to create hydrogen as fuel for vehicles.

Decomposition (continued) Example: 2 H2O → 2 H2 + O2 Example: 2 NI3 → N2 + 3 I2 *Note that although decomposition reactions can involve elements or compounds, metals or non-metals, the only ones you will have to predict the products for will be ionic or molecular compounds. Ionic compounds will form a metal and a non-metal, and molecular compounds will form two non-metals.

Practice Potassium Nitride → Diphosphorus pentoxide →

3. Single Displacement A single displacement reaction is a chemical change that involves an element and a compound as reactants. General Formula: M + AB → MB + A (metal as element) N + AB → A + NB (non-metal as element) In single displacement, an ionic compound is always a reactant, along with either a metal or a non-metal on its own. When the ionic compound is water or an acid, the metal will switch places with hydrogen, creating hydrogen gas.

Single Displacement (continued) Visual: solid, shiny precipitate usually forms when the metal comes out of solution, gas bubbles if there is a non-metal, and the solution itself can change colour. Real-Life Example: extracting expensive metals from minerals and rock in mining (take a cheaper metal and displace a more expensive metal in an ionic solution). Example: Mg + 2 AgNO3 → 2 Ag + Mg(NO3)2 Example: Br2 + CaI2 → I2 + CaBr2

Practice Sodium + Copper (II) Chloride → Fluorine + Iron (III) Phosphide →

Practice Zinc + Water → Aluminum + Hydrochloric Acid →

4. Double Displacement A double displacement reaction involves elements in different compounds displacing each other or exchanging places. General Formula: AB + CD → AD + BC A clue that the reaction is double displacement is that two ionic compounds are involved. Visuals: the two reactants are always aqueous, while one of the products will be a solid precipitate or water. Real-Life Example: neutralizing acids and bases to create water.

Double Displacement (continued) Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3 CaCO3 + 2 HCl → H2CO3 + CaCl2 H2SO4 + 2 NaOH → 2 H2O + Na2SO4

Practice Sodium chloride + silver nitrate → Magnesium sulfate + Iron (III) oxide → Hydrochloric acid + magnesium hydroxide →

5. Combustion A combustion reaction occurs when a hydrocarbon (a compound made of hydrogen and carbon) reacts with oxygen to produce water vapour, carbon dioxide, and energy in the form of heat. General Formula: CxHy + O2 → H2O + CO2 Since it releases energy, it is an exothermic reaction. Visuals - large amounts of heat and/or light can be seen, and possibly an explosion. Real-Life Example: the burning of fossil fuels, using a gas BBQ, how a car runs.

Combustion (continued) Example: CH4 + 2 O2 → CO2 + 2 H2O Example: C3H8 + 5 O2 → 3 CO2 + 4 H2O Combustion’s Environmental Impact Combustion of hydrocarbons releases carbon dioxide gas into the atmosphere. Carbon dioxide is a greenhouse gas, which means it plays a role in global warming. The excess carbon dioxide can prevent thermal energy (heat) from escaping into space, thus warming our planet. Combustion can also help the environment. When an oil spill occurs on land or water, it must first be set on fire before any contaminated soil can be removed for treatment, or before sponges can absorb the contaminated water.

Incomplete Combustion Incomplete combustion occurs when oxygen is limited – instead of getting carbon dioxide as a product, carbon monoxide is produced (poisonous gas) or solid carbon (black soot), along with water.

Practice Dicarbon tetrahydride + oxygen → Tetracarbon hexahydride + oxygen → Pentacarbon octahydride + oxygen →