Chemical Reactions and Conservation of Mass

This page introduces fundamental concepts in chemical reactions, focusing on word equations, conservation of mass, and balanced symbol equations.

Word equations are used to represent chemical reactions, with reactants on the left side of the arrow and products on the right. The arrow signifies the transformation of reactants into new substances.

Definition: A word equation is a way to represent a chemical reaction using the names of substances instead of chemical symbols.

Conservation of mass is a key principle in chemical reactions. It states that the total mass of reactants equals the total mass of products.

Highlight: In a reaction, the amount of each type of atom remains constant, but they are rearranged to form new products.

If it appears that mass has been lost during a reaction, it often means that a gas has been produced and escaped, accounting for the seemingly lost mass.

Balanced symbol equations provide a more detailed representation of chemical reactions. They use symbols from the Periodic Table and show:

1. Formulae of reactants and products
2. How atoms are rearranged
3. Relative amounts of reactants and products

Example: The balanced equation for the formation of water is 2H₂ + O₂ → 2H₂O

Vocabulary: Reactants are the starting substances in a chemical reaction, while products are the substances formed as a result of the reaction.

This page provides essential Chemical reactions KS3 revision material, helping students understand the basics of representing and analyzing chemical reactions.

Combustion and Thermal Decomposition

This page delves into two important types of chemical reactions: combustion and thermal decomposition, providing crucial Chemical reactions KS3 Worksheet content.

Combustion is the burning of a fuel in oxygen. A fuel is a substance that stores energy in a chemical form.

Definition: Combustion is a chemical reaction where a fuel burns in the presence of oxygen, releasing energy in the form of heat and light.

When a carbon-based fuel undergoes combustion, it produces water and carbon dioxide.

Example: The combustion equation for methane is: methane + oxygen → carbon dioxide + water

Hydrogen can be used as an alternative fuel, which is more environmentally friendly as it doesn't produce carbon dioxide.

Highlight: The combustion of hydrogen only produces water: hydrogen + oxygen → water

Thermal decomposition is a reaction where substances are broken down using heat.

Definition: Thermal decomposition is a chemical reaction where a compound breaks down into simpler substances when heated.

An example of thermal decomposition is the breakdown of metal carbonates:

Example: zinc carbonate → zinc oxide + carbon dioxide

This reaction can be tested by bubbling the produced gas through limewater. If the limewater turns cloudy, it confirms the presence of carbon dioxide.

Vocabulary: Limewater is a solution of calcium hydroxide used to test for the presence of carbon dioxide.

This page provides essential information for understanding combustion and chemical reactions combined science gcse topics, as well as thermal decomposition reaction examples for students.