Gases and Their Properties

States of Matter and the Kinetic Molecular Theory

The three primary states of matter are solids, liquids, and gases. Gases differ from solids and liquids in several key ways, as described by the Kinetic Molecular Theory:

• Gas molecules move rapidly and randomly, with large distances between them.

• They have negligible volume compared to the container.

• Gas particles experience elastic collisions (no energy lost).

• There are no significant attractive or repulsive forces between gas molecules.

• The average kinetic energy of gas molecules is proportional to the temperature (in Kelvin).

Example: Air in a balloon expands when heated because the kinetic energy of the gas molecules increases, causing them to move faster and occupy more space.

Pressure and Its Measurement

Pressure is defined as the force exerted per unit area by gas molecules as they collide with the surfaces of their container.

• Common units: atmospheres (atm), millimeters of mercury (mmHg), and torr.

• 1 atm = 760 mmHg = 760 torr

STP (Standard Temperature and Pressure): Defined as 0°C (273 K) and 1 atm pressure. At STP, 1 mole of any ideal gas occupies 22.4 L.

Gas Laws

Gas laws describe the relationships between pressure (P), volume (V), temperature (T), and amount (n) of a gas.

• Boyle's Law: At constant temperature, pressure and volume are inversely related.

• Charles's Law: At constant pressure, volume and temperature are directly related.

• Gay-Lussac's Law: At constant volume, pressure and temperature are directly related.

• Combined Gas Law: Combines Boyle's, Charles's, and Gay-Lussac's laws.

• Ideal Gas Law: Relates all four variables:

• Dalton's Law of Partial Pressures: The total pressure of a gas mixture is the sum of the partial pressures of each component:

Units:

• Pressure: atm, mmHg, torr

• Volume: liters (L)

• Temperature: Kelvin (K) (always use Kelvin in gas law calculations)

• Amount: moles (mol)

Example: If the pressure on a gas is increased while temperature is constant, the volume decreases (Boyle's Law).

Conversions and Calculations

• To convert Celsius to Kelvin:

• To convert between pressure units: 1 atm = 760 mmHg = 760 torr

• To convert grams to moles:

• Use mole ratios from balanced equations to relate amounts of reactants and products.

Atmospheric Pressure and Altitude

• Atmospheric pressure decreases as altitude increases.

• Boiling point of water decreases at higher altitudes due to lower atmospheric pressure.

Solutions and Their Properties

Definitions

• Solution: A homogeneous mixture of two or more substances.

• Solvent: The substance present in the greatest amount; dissolves the solute.

• Solute: The substance being dissolved.

• Electrolytes: Substances that conduct electricity when dissolved in water (strong, weak, or nonelectrolytes).

Example: In saltwater, water is the solvent and sodium chloride is the solute.

Solubility and Solubility Rules

• Saturated solution: Contains the maximum amount of solute that can dissolve at a given temperature.

• Unsaturated solution: Contains less solute than the maximum amount that can dissolve.

• Solubility of solids generally increases with temperature; solubility of gases decreases with temperature.

• "Like dissolves like": Polar solutes dissolve in polar solvents; nonpolar solutes dissolve in nonpolar solvents.

Effect of Solute on Boiling and Freezing Points

• Adding a solute to water raises the boiling point and lowers the freezing point (colligative properties).

• Electrolytes have a greater effect than nonelectrolytes because they produce more particles in solution.

Molarity and Dilution

• Molarity (M): The concentration of a solution, defined as moles of solute per liter of solution:

• Units for molarity: mol/L

• To calculate molarity, convert grams to moles if necessary, and volume to liters.

• Dilution equation: (where C = concentration, V = volume)

Example: To prepare 250 mL of 0.5 M NaCl from a 2.0 M stock solution, use the dilution equation to find the required volume of stock solution.

Equivalents and Ions

• Equivalent (Eq): The amount of an ion that supplies 1 mole of charge.

• Number of equivalents per mole of ion = absolute value of the ion's charge.

• Example: 1 mole of Ca2+ provides 2 equivalents.

Hydrogen Bonding

• Hydrogen bonding occurs when hydrogen is bonded to fluorine (F), oxygen (O), or nitrogen (N).

• These interactions are responsible for many unique properties of water and biological molecules.

Summary Table: Gas Laws and Their Relationships

Additional info:

• Solubility rules are used to predict whether a compound will dissolve in water; refer to your textbook or provided chart for specific rules.

• For all gas law calculations involving temperature, always use Kelvin.

• When interpreting solubility rules, remember that most nitrates (NO3-) and alkali metal salts are soluble.