Some Basic Concepts in Chemistry Cheatsheet
Cheat Codes & Shortcuts
- Mole: SI unit for amount of substance; contains \(6.022 \times 10^{23}\) particles (Avogadro's number).
- Molar Mass: Mass of one mole in grams; \( \text{M} = \frac{\text{mass}}{\text{moles}} \).
- Empirical Formula: Simplest whole-number ratio of atoms.
- Molecular Formula: Actual number of atoms of each element in a molecule.
- Stoichiometry: Use balanced equations to relate moles, mass, & volume.
- Limiting Reagent: Reactant that runs out first, limits product formed.
- Atomic Mass Unit (amu): \(1\,\text{amu} = 1/12\) mass of a carbon-12 atom.
- Law of Conservation of Mass: Mass is neither created nor destroyed in chemical reactions.
- Percentage Composition: \( \% = \frac{\text{mass of element}}{\text{total mass}} \times 100 \).
- Avogadro's Law: Equal volumes of gases at same T and P contain equal number of molecules.
Quick Reference Table
| Term | Definition / Formula | Example / Note |
|---|---|---|
| Mole | \(1\,\text{mole} = 6.022 \times 10^{23}\) entities | 1 mole of Na = \(6.022 \times 10^{23}\) atoms Na |
| Molar Mass | \(\text{M} = \frac{\text{mass (g)}}{\text{moles}}\) | Molar mass H\(_2\)O = 18.02g/mol |
| Empirical Formula | Simplest ratio (CH for C\(_6\)H\(_6\)) | Benzene: empirical = CH, molecular = C\(_6\)H\(_6\) |
| Stoichiometry | Balanced equation gives mole ratios | \(2H_2 + O_2 \rightarrow 2H_2O\): 2:1:2 ratio |
| Limiting Reagent | Least moles consumed first | Calculates max possible product |
| Atomic Mass | \(\text{Relative mass compared to C-12}\) | C = 12.00 amu by definition |
| % Composition | \(\frac{\text{mass of element}}{\text{total mass}} \times 100\) | H in H\(_2\)O: (2/18)×100=11.1% |
Advice
Step 1: Always check units: grams, moles, liters.
Step 2: For formulas, reduce to *empirical form* first.
Step 3: When calculating product, always identify the limiting reagent.
Step 4: Use Avogadro's number for particle conversions.
Step 5: Balance equations for stoichiometry before calculations.
Chemistry Quick Tips
- Converting grams → moles: \( \text{n} = \frac{\text{mass}}{\text{molar mass}} \).
- Empirical formula steps: Convert mass to moles, divide by smallest, round to nearest whole number.
- Mole concept: Use Avogadro’s number whenever particles are asked.
- Volume of gas at STP: \(1\,\text{mol} = 22.4\,\text{L}\) (for ideal gases at STP).
- Limiting reagent: Compare mole ratios from balanced equation.
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