KS3 Chemistry: Chemical Changes Review

Vocabulary practice covering chemical and physical changes, gas testing, conservation of mass, and environmental impacts of combustion.

Effervescence

The bubbling or fizzing observed in a chemical reaction when a gas is produced as one of the products.

Test for Hydrogen

Placing a burning splint near a test tube which results in a "squeaky pop" or a small explosion.

Test for Oxygen

Placing a glowing splint near a test tube which results in the gas relighting the splint.

Test for Carbon Dioxide

Passing bubbles of gas through a delivery tube into limewater; the gas turns the limewater cloudy.

Composition of Nitrogen in Air

$78\%$.

Composition of Oxygen in Air

$21\%$.

Chemical Change

Occurs when particles change as new compounds are formed, often observed by temperature change or colour change.

Physical Change

Occurs when particles are rearranged but not individually changed, such as a change of state or forming/separating a mixture.

Principle of Conservation of Mass

The total mass of all reactants before a chemical reaction is equal to the total mass of all products after the reaction.

Exothermic Reaction

A reaction where energy is released, often as light, sound, or heat, resulting in a temperature increase.

Endothermic Reaction

A reaction where energy is taken in from the surroundings, resulting in a temperature decrease.

Reactants

The substances present at the start of a reaction, always shown to the left of the arrow in a chemical equation.

Products

The final substances formed in a reaction, always shown to the right of the arrow in a chemical equation.

State Symbol (aq)

The abbreviation used in a symbol equation to represent an aqueous solution.

Combustion

A type of chemical reaction where a substance is heated and reacts with oxygen to form an oxide.

Oxidation

A chemical reaction in which oxygen is added to a substance.

Hydrocarbon

A compound containing carbon and hydrogen only, such as methane.

Complete Combustion

Occurs when there is enough oxygen present to ensure all the carbon in a fuel forms carbon dioxide.

Incomplete Combustion

Occurs when there is not enough oxygen present, potentially producing carbon monoxide ($CO$) or soot.

Soot

Fine particles of carbon produced during incomplete combustion that can cause respiratory problems.

Acid Rain

Lowering of rain's pH caused by sulfur dioxide or nitrogen oxides dissolving in clouds to form sulfuric or nitric acids.

CFCs (chlorofluorocarbons)

Chemicals formerly used in aerosols and refrigerators that deplete the ozone layer.

Carbon Footprint

A term used to describe an individual's or group's impact on the environment regarding the release of carbon dioxide and other greenhouse gases.

Fire Triangle

A simple representation of the three things needed for burning: Fuel, Heat, and Oxygen.