GOB Chemistry Study Notes: Moles, Gas Laws, and Solutions

Moles and Stoichiometry

Basic Concepts of the Mole

The mole is a fundamental unit in chemistry used to express amounts of a chemical substance. It allows chemists to count entities at the atomic and molecular scale.

• Mole: The amount of substance containing as many entities (atoms, molecules, ions) as there are atoms in 12 grams of carbon-12.

• Avogadro's Number: $6.022 \times 10^{23}$ entities per mole.

• Molar Mass: The mass of one mole of a substance, expressed in grams per mole (g/mol).

Example: 1 mole of H2O contains $6.022 \times 10^{23}$ molecules and has a mass of 18.02 g.

Stoichiometry and Conversions

Stoichiometry involves quantitative relationships between reactants and products in chemical reactions.

• Moles to Grams: $\text{mass (g)} = \text{moles} \times \text{molar mass (g/mol)}$

• Grams to Moles: $\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$

• Moles to Atoms/Molecules: $\text{number of entities} = \text{moles} \times 6.022 \times 10^{23}$

Example: Convert 10 g of NaCl to moles: $\text{moles} = \frac{10}{58.44} = 0.171$ mol

Thermochemistry

Chemical reactions can be classified based on heat exchange:

• Exothermic: Releases heat to surroundings.

• Endothermic: Absorbs heat from surroundings.

Example: Combustion of methane is exothermic.

Gas Laws and Kinetic Molecular Theory

Kinetic Molecular Theory of Gases

This theory explains the behavior of gases in terms of particle motion.

• Gases consist of tiny particles in constant, random motion.

• Collisions between particles are elastic.

• Volume of gas particles is negligible compared to container volume.

Boyle's Law

Describes the inverse relationship between pressure and volume at constant temperature.

• Equation: $P_1V_1 = P_2V_2$

• Example: If a gas at 2.0 L and 1.0 atm is compressed to 1.0 L, the new pressure is 2.0 atm.

Charles's Law

Relates volume and temperature at constant pressure.

• Equation: $\frac{V_1}{T_1} = \frac{V_2}{T_2}$

• Example: Heating a balloon increases its volume.

Gay-Lussac's Law

Relates pressure and temperature at constant volume.

• Equation: $\frac{P_1}{T_1} = \frac{P_2}{T_2}$

Avogadro's Law

Relates volume and number of moles at constant temperature and pressure.

• Equation: $\frac{V_1}{n_1} = \frac{V_2}{n_2}$

Dalton's Law of Partial Pressures

The total pressure of a mixture of gases is the sum of the partial pressures of each gas.

• Equation: $P_{\text{total}} = P_1 + P_2 + P_3 + \ldots$

Molar Volume and STP

At standard temperature and pressure (STP: 0°C, 1 atm), one mole of any ideal gas occupies 22.4 L.

• Equation: $\text{Molar Volume at STP} = 22.4 \text{ L/mol}$

Barometer and Atmospheric Pressure

A barometer measures atmospheric pressure, often using mercury.

• Atmospheric pressure at sea level is 1 atm or 760 mmHg.

Solutions and Their Properties

Types of Solutions and Solutes

Solutions are homogeneous mixtures of solute and solvent.

• Solute: Substance dissolved in a solvent.

• Solvent: Substance that dissolves the solute (often water).

• Types of solutes: Polar, nonpolar, strong/weak electrolytes, nonelectrolytes.

Saturation and Concentration

Describes the amount of solute dissolved in a solvent.

• Saturated Solution: Contains maximum amount of solute at given conditions.

• Unsaturated Solution: Can dissolve more solute.

Effect of Temperature on Solubility

Temperature affects solubility of solids and gases differently.

• Solubility of solids generally increases with temperature.

• Solubility of gases generally decreases with temperature.

Concentration Units

Several ways to express concentration:

• Mass Percent: $\text{Mass percent} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$

• Volume Percent: $\text{Volume percent} = \frac{\text{volume of solute}}{\text{volume of solution}} \times 100\%$

• Molarity (M): $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

Dilution Formula

Used to calculate concentration after dilution.

• Equation: $M_1V_1 = M_2V_2$

Types of Solutions: Isotonic, Hypertonic, Hypotonic

These terms describe the relative concentration of solutes in solutions separated by a membrane.

• Isotonic: Equal solute concentration inside and outside the cell.

• Hypertonic: Higher solute concentration outside the cell; water moves out.

• Hypotonic: Lower solute concentration outside the cell; water moves in.

Colloids, Suspensions, and Solutions

Classification based on particle size and stability.

Type	Particle Size	Appearance	Stability
Solution	< 1 nm	Clear	Stable, does not settle
Colloid	1-1000 nm	Cloudy	Stable, does not settle
Suspension	> 1000 nm	Cloudy	Unstable, particles settle

Example: Salt water is a solution; milk is a colloid; muddy water is a suspension.

Additional info: Some context and definitions were inferred for completeness and clarity, especially for solution types and concentration units.