Chapter 1 / 1.5 Laws Of Chemical Combination

Unit Conversion Magic ✨

When converting units, we use unit factors (fractions equal to 1). Multiply them to switch units without changing the value!

Examples:

Inches to cm: $$3 \text{ in} = 3 \text{ in} \times \frac{2.54 \text{ cm}}{1 \text{ in}} = 7.62 \text{ cm}$$ Tip: Cancel matching units! ✅
Liters to m³: $$2 \text{ L} = 2000 \text{ cm}^3 \times \left(\frac{1 \text{ m}}{100 \text{ cm}}\right)^3 = 0.002 \text{ m}^3$$ Cubing unit factors? Easy-peasy! 📦
Days to seconds: $$2 \text{ days} = 2 \times 24 \times 60 \times 60 \text{ s} = 172,\!800 \text{ s}$$ Chain those conversions! ⛓️

5 Laws of Chemical Combinations 🔬

1. Law of Conservation of Mass

⚖️ Antoine Lavoisier (1789): Mass can’t be created or destroyed in chemical reactions. Reactant mass = Product mass.

Example: Burning wood? Ash + gas mass = original wood mass!

2. Law of Definite Proportions

🧪 Joseph Proust: Compounds always have the same element ratio by mass, no matter how they’re made.

Proof: Natural vs. synthetic copper carbonate both had:
$$\%\text{ Cu} = 51.35,\quad \%\text{ C} = 9.74,\quad \%\text{ O} = 38.91$$

3. Law of Multiple Proportions

🔢 John Dalton (1803): When 2 elements form multiple compounds, masses of one element per fixed mass of the other are in whole-number ratios.

Example: Hydrogen + Oxygen →
Water: 2g H : 16g O (O:H = 16:2)
Hydrogen peroxide: 2g H : 32g O (O:H = 32:2)
Ratio = 16:32 = 1:2 ✨

4. Gay Lussac’s Law of Gaseous Volumes (1808)

💨 Gases react in simple volume ratios at same T & P.

Example: Hydrogen + Oxygen → Water vapor:
$$100 \text{ mL H}_2 + 50 \text{ mL O}_2 \rightarrow 100 \text{ mL steam}$$ Ratio = 100:50 = 2:1

5. Avogadro’s Law (1811)

🌫️ Equal gas volumes (same T & P) have equal molecules.

Example: 2 H₂ + O₂ → 2 H₂O means:
2 volumes H₂ + 1 volume O₂ → 2 volumes steam