Chemical reactions

Assumed perquisite knowledge:

Students understand the difference between a physical change and a chemical change

Introduction

1. A chemical reaction occurs when substances combine or breakdown to produce something NEW.
2. A chemical reaction is accompanied by a chemical change. eg. permanment change in color or the production of a gas.

   Chemical changes indicate that something new has been produced. eg. the permanent color change produced as bread is toasted in a toaster or the smoke from a burning match.

3. Chemical reactions are generally difficult to reverse. eg. turning a slice of toast into a slice of fresh bread.

The chemicals that react are called the reactants. The new materials that are produced are called the products.

A chemical reaction can be shown by the use of a word equation. The ==> means 'give or produce'

Types of chemical reactions.

• There are many different types of reactions which include
• Corrosion of metals. Eg. The rusting of iron
• Combustion: Eg. The burning of fossil fuels
• Acid and base : Eg. Hydrochloric acid and sodium hydroxide.
• Acid and carbonate: Eg. Vinegar and bicarb of soda
• Acid and active metal: This type of reaction is also called a single displacement reaction. Eg. The dissolving of magnesium ribbon in hydrochloric acid.
• Precipitation: This type of reaction is also called a double displacement reaction. Eg. Mixing colorless lead nitrate and potassium iodide to yellow produce lead iodide.
• Decomposition: Eg. Hydrogen peroxide being broken down into water and oxygen
• Synthesis: Eg. The burning of magnesium in air to produce magnesium oxide.
• Displacement:. Eg. The production of copper wool by from steel wool being placed into a solution of copper sulphate.
• Redox (Reduction/ Oxidation): Eg. Making a battery.
• Condensation: Eg. Glucose and Fructose producing sucrose
• Dehydration: Eg. Adding concentrated sulphuric acid to sugar
• Substituion: Eg. Bromine reacting with octane in the presence of UV light.
• Addition: Eg. Adding bromine to cyclohexene
• Polymerisation: Eg. making Nylon, polyethylene
• Fermentation: Eg. The making of wine
• Exothermic: Eg. The thermite reaction is used to weld rail tracks together. The reaction is so hot molten iron is produced!
• Endothermic: Eg. An ice pack. Mix the contents inside the packet and the mixture becomes cold