Study Notes
Chemical reactions involve the transformation of substances into new ones, with different properties and compositions. They are not easily reversible and can be identified by indicators such as color change, effervescence, precipitation, temperature change, smell, and sound.
- Physical Change — a change in which the matter's physical appearance is altered, but composition remains unchanged. Example: Melting ice into water.
- Chemical Change — a change that alters the composition of the original matter, resulting in new substances. Example: Burning wood to produce ash and smoke.
- Reactants — substances that are involved in a chemical reaction and are changed by it. Example: Hydrogen and oxygen in the formation of water.
- Products — substances that are produced by a chemical reaction. Example: Water formed from hydrogen and oxygen.
- Combustion — a reaction where a substance burns in oxygen, releasing energy. Example: Methane burning in a Bunsen burner.
- Thermal Decomposition — a reaction where a single reactant breaks down into two or more products when heated. Example: Copper carbonate decomposing into copper oxide and carbon dioxide.
Exam Tips
Key Definitions to Remember
- Physical Change: A change in physical appearance without altering composition.
- Chemical Change: A change that alters the composition of the original matter.
- Reactants: Substances changed by a chemical reaction.
- Products: Substances produced by a chemical reaction.
- Combustion: Reaction of a substance with oxygen, releasing energy.
- Thermal Decomposition: A single reactant breaking down into multiple products when heated.
Common Confusions
- Confusing physical changes with chemical changes.
- Thinking that all reactions are reversible.
Typical Exam Questions
- What is a chemical reaction? A process where substances change to produce new substances.
- What are the indicators of a chemical reaction? Color change, effervescence, precipitation, temperature change, smell, and sound.
- What happens during combustion? A substance reacts with oxygen, releasing energy.
What Examiners Usually Test
- Understanding the difference between physical and chemical changes.
- Identifying reactants and products in a chemical reaction.
- Recognizing indicators of chemical reactions.