Year 9 Chemical reactions

Chemical Reaction

A process in which starting substances undergo a chemical change to form one or more entirely new substance(s)

Reactant

A starting substance consumed during the course of a chemical reaction.

Product

A new substance formed as a result of a chemical reaction

Evidence of a chemical reaction

Gas production, precipitate formation, temperature changes, or permanent colour changes

Precipitate

An insoluble solid substance that emerges out of a liquid solution during a chemical reaction.

Reaction Arrow (➔)

'reacts to form', separating reactants from products, and must never be substituted with an equals sign (=).

Coefficient

The full-sized number placed intentionally in front of a chemical formula within an equation. Adjusting coefficients is the only way to balance an equation.

Subscript

The small-sized number embedded within a chemical formula indicating the ratio of atoms in that compound. Do not change the subscript when balancing.

Conservation of Mass (atoms)

Atoms are neither created nor destroyed during a chemical reaction. Same number of each atom on both sides of an equation.

Acid

A chemical substance that has a pH less than 7 and turns Red, Orange or Yellow in universal indicator.

Base

A substance that has a pH greater than 7 and turns blue or purple in universal indicator.

pH Scale

A scale running from 0 to 14 used to measure and rank how strongly acidic, neutral, or basic a solution is.

Indicator

A chemical dye that undergoes distinct, predictable colour variations depending on the pH level of the solution it is added to.

Neutralisation

When an acid and a base are added producing a neutral solution composed of a salt and water (Acid + Base ➔ Salt + Water).

Exothermic Reaction

A chemical reaction that transfers thermal energy outward to its surroundings, causing the surrounding temperature to increase.

Endothermic Reaction

A chemical reaction that absorbs thermal energy inward from its surroundings, causing the surrounding temperature to decrease.

Combustion

A chemical reaction between a fuel and an oxidiser (oxygen) that releases energy outward as visible light and heat energy.

Fuel

A high-energy chemical reactant like hydrocarbons e.g. butane, pentane, methane.

Hydrocarbon

An organic chemical compound composed of hydrogen and carbon atoms, commonly serving as fuel (e.g., methane, propane).

Complete Combustion

A reaction pattern occurring when a hydrocarbon fuel reacts completely in an environment with an abundant oxygen supply, producing carbon dioxide and water vapour as products.

Displacement

A competitive reaction pattern in which a metal of higher chemical reactivity displaces (forces out) a less reactive metal from its aqueous salt solution compound.

Reactivity Series

Ranking metals relative to one another in descending order of their chemical reactivity.

Aim

The purpose or intended outcome of an experiment.

Independent Variable

The variable that is changed.

Dependent Variable

The variable that is measured.

Controlled Variables

The variables that are kept the same to make the test fair.

Fair Test

An experiment where only one variable is changed.

Reliable Results

Results that are trustworthy and consistent when repeated.

Repeat

Doing the experiment more than once to produce accurate and reliable results.

Anomaly

A result that does not fit the pattern of the other results.