Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define reactants and products and identify them in reactions.
• Represent simple reactions using word equations.
• Distinguish between reactants and products in word equations.
• Explain the law of conservation of mass.
• Predict products of simple reactions based on observations.

Lesson summary

Chemical reactions are fundamental processes that occur all around us, constantly transforming matter from one form to another. Understanding chemical reactions, particularly the roles of reactants and products, is crucial for comprehending many aspects of the world, from cooking a meal in your kitchen to the industrial processes that produce essential goods. In South Africa, a grasp of chemistry is vital in various industries, including mining, agriculture, and manufacturing, contributing to economic growth and job creation. Chemical reactions are also essential for life processes like digestion and photosynthesis, making this topic incredibly relevant to your understanding of biology too.

Lesson notes

What is a Chemical Reaction? A chemical reaction is a process that involves the rearrangement of atoms and molecules to form new substances. This rearrangement results in a change in the chemical properties of the substances involved. Chemical reactions are often accompanied by observable changes, such as a change in colour, the formation of a gas (bubbling), the formation of a precipitate (a solid forming in a liquid mixture), or a change in temperature (either heat being released or absorbed).

Reactants: The Starting Materials Reactants are the substances that start the chemical reaction. They are the materials that undergo a change to form new substances. Reactants are usually written on the left-hand side of a chemical equation. Think of them as the ingredients in a recipe.

Products: The New Substances Formed Products are the new substances that are formed as a result of the chemical reaction. They are the substances that you end up with after the reaction has taken place. Products are usually written on the right-hand side of a chemical equation. Think of them as the final dish you create. Word Equations A word equation is a simple way to represent a chemical reaction using the names of the reactants and products. The reactants are written on the left, followed by an arrow (→), and then the products on the right. The arrow means "reacts to form" or "produces." For example: `Methane + Oxygen → Carbon dioxide + Water` In this reaction, methane and oxygen are the reactants, and carbon dioxide and water are the products. This reaction is what happens when you burn natural gas (mostly methane) in a stove or heater. Law of Conservation of Mass A crucial principle in chemical reactions is the Law of Conservation of Mass. This law states that matter cannot be created or destroyed in a chemical reaction. This means that the total mass of the reactants must equal the total mass of the products. Atoms are simply rearranged, not created or destroyed. This explains why balancing chemical equations is so important (although we don't formally balance equations at Grade 8 level, this sets the stage for future learning). Examples of Chemical Reactions and Identifying Reactants and Products: Rusting of Iron: Word equation: `Iron + Oxygen → Iron Oxide (Rust)` Reactants: Iron and Oxygen Product: Iron Oxide (Rust)

Real-life Application in South Africa: Rusting is a significant problem for infrastructure like bridges and pipelines, necessitating regular maintenance and protective coatings.

Photosynthesis (simplified): Word equation: `Carbon Dioxide + Water → Glucose + Oxygen` Reactants: Carbon Dioxide and Water Products: Glucose and Oxygen Real-life Application in South Africa: Photosynthesis is essential for agriculture, providing the energy and building blocks for crops that feed the nation.

Burning Wood: Word equation: `Wood + Oxygen → Carbon Dioxide + Water + Ash` Reactants: Wood and Oxygen Products: Carbon Dioxide, Water, and Ash Real-life Application in South Africa: Many rural communities rely on wood for cooking and heating, making understanding combustion important.

Reaction of Vinegar and Baking Soda: Word equation: `Vinegar + Baking Soda → Carbon Dioxide + Water + Sodium Acetate` Reactants: Vinegar (acetic acid) and Baking Soda (sodium bicarbonate)

Products: Carbon Dioxide, Water and Sodium Acetate

Worked example

Consider the reaction where calcium carbonate (limestone) reacts with hydrochloric acid to produce calcium chloride, water, and carbon dioxide. This is a reaction that often occurs when acid rain acts on limestone buildings.

Word equation: `Calcium Carbonate + Hydrochloric Acid → Calcium Chloride + Water + Carbon Dioxide`

Reactants: Calcium Carbonate and Hydrochloric Acid

Products: Calcium Chloride, Water, and Carbon Dioxide

Guided Practice (With Solutions)

Question 1: