Chemical Reactions
1. Physical and Chemical Properties of Common Materials:
- Physical properties are observable without changing the material's chemical makeup (e.g., color, hardness, melting point, density).
- Chemical properties describe how a substance interacts with others (e.g., flammability, reactivity with acids).
2. Classifying Physical vs. Chemical Changes:
- Physical change: The substance’s form or state changes but not its chemical makeup (e.g., melting ice, dissolving salt in water).
- Chemical change: The substance’s composition changes, producing new substances (e.g., rusting iron, burning wood).
3. Indicators of a Chemical Change:
- Signs include color change, temperature change, gas formation, precipitate formation, and changes in odor.
4. Reactants and Products in a Chemical Reaction:
- Reactants are the starting substances in a reaction, and products are the substances formed after the reaction (e.g., in the reaction of hydrogen and oxygen, hydrogen and oxygen are reactants, and water is the product).
5. Definition of “Rate” of a Reaction:
- The rate of reaction refers to how fast reactants are converted into products in a chemical reaction.
6. Examples of Wanted and Unwanted Reactions:
- Wanted reactions: Photosynthesis, baking, digestion.
- Unwanted reactions: Rusting, food spoilage, corrosion of metals.
7. Elements as Building Blocks of Matter:
- Elements are pure substances that consist of only one type of atom. They cannot be broken down further by chemical means.
8. Matter as Particles: Atoms and Molecules:
- Matter is made up of atoms (single units of elements) and molecules (groups of atoms bonded together).
9. Definition of an Atom:
- An atom is the smallest particle of an element that retains its chemical properties. Atoms are the fundamental units of matter.
10. Interpreting Diagrams and Identifying Substances:
- Elements: Single type of atom (e.g., O₂).
- Compounds: Two or more different atoms bonded (e.g., H₂O).
- Pure substances: Made of only one type of element or compound.
- Mixtures: Combination of elements or compounds that are not chemically bonded (e.g., air).
11. Arrangement of Subatomic Particles in Atoms:
- Atoms have a nucleus with protons and neutrons, while electrons orbit around the nucleus.
12. Names and Symbols of Key Elements:
- First 20 elements: H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca.
- Important symbols: Fe (Iron), Cu (Copper), Ag (Silver), Au (Gold), Zn (Zinc), Hg (Mercury).
13. Identifying Elements, Compounds, and Mixtures with Symbols and Formulae:
- Elements have one symbol (e.g., O for oxygen).
- Compounds have formulae with different element symbols (e.g., CO₂ for carbon dioxide).
- Mixtures can include multiple elements/compounds, not written in a single formula.
14. Physical and Chemical Properties of Oxygen, Hydrogen, and Carbon Dioxide:
- Oxygen (O₂): Supports combustion, colorless, odorless.
- Hydrogen (H₂): Highly flammable, lightest gas, colorless.
- Carbon dioxide (CO₂): Non-flammable, denser than air, colorless, acidic.
15. Tests for O₂, CO₂, and H₂:
- O₂: Relights a glowing splint.
- CO₂: Turns limewater cloudy.
- H₂: Produces a popping sound with a lit splint.
16. Uses Based on Chemical Properties of O₂, CO₂, and H₂:
- O₂: Used in respiration, supports combustion in medical and industrial applications.
- CO₂: Used in fire extinguishers, carbonated drinks, and as a greenhouse gas in plant growth.
- H₂: Used as a fuel, in fuel cells, and as a reducing agent in chemical reactions.
17. Effect of Carbon Dioxide on the Environment:
- CO₂ is a greenhouse gas that contributes to global warming and climate change by trapping heat in the atmosphere. Increased CO₂ levels also lead to ocean acidification.