Chemical Reactions Overview

Chemical Reactions

• Chemical reaction: Substances react to form new substances with different chemical properties.

Definitions

• Reactants: Substances that react with each other.
• Products: Substances formed from the reaction.
• Chemical change: A reaction that forms new products.
• Physical change: A change in state (phase) without changing the chemical form.

Parts of a Chemical Reaction

• Reactants are the starting substances.
• Products are the substances formed in the reaction.
• Example: 2H₂(g) + O₂(g) → 2H₂O(l)
  • Reactants: 2H₂ (g) , O₂(g)
  • Product: 2H₂O(l)

How to Tell if a Chemical Reaction is Taking Place

• Color change
• Gas production (bubbles, fizzing)
• Temperature change (heat or cold)
• Formation of a precipitate (solid forming from a liquid)
• Smell

Examples of Chemical Changes

• Burning wood
• Rotting fruit
• Baking a cake
• Rusting metal
• Using a battery
• Digestion
• Souring milk
• Exploding fireworks
• Cooking an egg
• Photosynthesis

Class Activity

• Examples of chemical changes.
• Signs of chemical change for each example.

Homework

• Page 48 classify substances.
• Revision exercise question 1-4.
• Complete balancing equations worksheet.
• Research examples of exothermic and endothermic reactions on page 55

Chemical Change

• Chemical change: New products are formed when old bonds break and new bonds form between products, resulting in a new product/molecule.
• Example: Rust

Phase Change

• Physical change: When a substance changes phases (solid, liquid, gas) the molecule remains the same, and it can return to its original form.
• Example: Water changing to steam

Energy Changes

• Exothermic reactions: More energy is given out than is required. Energy is lost to the surroundings, and the product is colder than the reactants.
• Example: Burning a candle
• Endothermic reactions: More energy has to be put in than is given out. Energy is taken from the surroundings, and the product is warmer than the reactants.
• Example: Baking bread

Types of Chemical Reactions

• Combustion
• Synthesis
• Acid-base reactions
• Decomposition

Combustion

• Oxygen combines with a compound to form carbon dioxide and water.
• Example: Fuel + O₂ → CO₂ + H₂O

Synthesis

• Two molecules interact to form a different molecule.
• Example: A + B → AB

Acid-Base Reactions

• A chemical reaction between an acid and a base forms water and a salt.
• Example: Acid + Base → H₂O + Salt

Decomposition

• A reactant breaks down into two or more products.
• Example: AB → A + B

Balancing Chemical Equations

• The number of atoms of each element must be the same on both sides of the equation.

This quiz covers the fundamental concepts of chemical reactions, including definitions of reactants and products, the distinction between chemical and physical changes, and indicators of a chemical reaction. Explore various examples and learn to identify when a chemical reaction occurs.