Chemistry Chapter: Acids and Alkalis

Two types of changes: Chemical and Physical.
Chemical changes create new substances (elements or compounds) and are typically permanent or difficult to reverse.
Reactants are substances that undergo a chemical change while products are the new substances formed.
Chemical changes can occur in two forms:
- Two or more substances combine to create new substances (e.g., carbon + oxygen → carbon dioxide + water).
- A substance breaks down into two or more new substances (e.g., calcium carbonate → calcium oxide + carbon dioxide).

The total number of atoms in reactants equals the total in products.
Example: H2 + O2 = H2O (2 atoms of Hydrogen + 1 atom of Oxygen = 3 atoms total).

Combustion:
- Reaction involving a substance burning in oxygen, producing heat and light (e.g., carbon in a barbecue produces carbon dioxide).
Thermal Decomposition:
- A substance breaks down into simpler substances when heated (e.g., calcium carbonate → calcium oxide + carbon dioxide).
Oxidation:
- Involves a substance gaining oxygen (e.g., rusting of iron leading to rust formation).
Cellular Respiration:
- Breakdown of food molecules (like glucose) in the presence of oxygen to release energy, producing carbon dioxide and water as byproducts.

Neutralization Reaction:
- Acids react with alkalis to form salt and water.
- Example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
Properties of Acids:
- Sour taste, can burn skin, turn blue litmus paper red, react with alkalis, metals, and carbonates.
Properties of Alkalis:
- Bitter taste, soapy feel, can burn skin, turn red litmus paper blue, react with acids.
Types of Reactions Involving Acids:
- Acid + Alkali → Salt + Water (e.g., hydrochloric acid + sodium hydroxide).
- Acid + Metal → Salt + Hydrogen (e.g., hydrochloric acid + magnesium → magnesium chloride + hydrogen).
- Acid + Carbonate → Salt + Carbon Dioxide + Water (e.g., hydrochloric acid + magnesium carbonate → magnesium chloride + carbon dioxide + water).
Common Acid Names:
- Hydrochloric acid → chloride
- Sulfuric acid → sulfate
- Nitric acid → nitrate

Hydrogen Test:
- Place a metal in acid, cover it, and add a lit splint. A 'pop' sound indicates hydrogen is present.
Carbon Dioxide Test:
- Mix acid with carbonate in one test tube and limewater in another. If limewater becomes murky, carbon dioxide was produced.

Two primary ways chemical changes occur:
- Mixing: Reactants combine irreversibly to form products.
- Heating: Increased temperature facilitates chemical reactions (e.g., combustion and thermal decomposition).