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

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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