Study Guide: Gases and Solutions (Chapters 8 & 9) – CHEM 1303

Chapter 8: Gases

Section 8.1: Properties of Gases

The study of gases involves understanding their physical properties and behavior. The molecular theory of gases explains how gas particles move and interact, and how these behaviors relate to measurable properties such as pressure, volume, temperature, and amount.

• Molecular Theory of Gases: Gases consist of particles (atoms or molecules) in constant, random motion. These particles are far apart compared to their size, and collisions between them are elastic.

• Units of Measurement:

  • Pressure: Measured in atmospheres (atm), pascals (Pa), torr, or millimeters of mercury (mmHg).

  • Volume: Measured in liters (L) or milliliters (mL).

  • Temperature: Measured in Kelvin (K) or degrees Celsius (°C). Always use Kelvin for gas law calculations.

  • Amount of Gas: Measured in moles (mol).

• Conversions: Know how to convert between units, e.g.,

• Example: A gas sample at 2.0 atm pressure occupies 1.5 L at 300 K.

Section 8.2: Pressure and Volume (Boyle’s Law)

Boyle’s Law describes the relationship between the pressure and volume of a gas when temperature and amount are constant. As pressure increases, volume decreases, and vice versa.

• Boyle’s Law Equation: $P_1 V_1 = P_2 V_2$

• Application: Used to calculate unknown pressure or volume.

• Biological Example: Inspiration (breathing in) increases lung volume, decreasing pressure and drawing air in; expiration (breathing out) decreases volume, increasing pressure and expelling air.

Section 8.3: Temperature and Volume (Charles’s Law)

Charles’s Law relates the volume of a gas to its temperature at constant pressure and amount. As temperature increases, volume increases.

• Charles’s Law Equation: $\frac{V_1}{T_1} = \frac{V_2}{T_2}$

• Application: Used to calculate unknown temperature or volume.

• Example: A balloon expands when heated because the gas inside increases in volume.

Section 8.4: Temperature and Pressure (Gay-Lussac’s Law)

Gay-Lussac’s Law describes the relationship between the pressure and temperature of a gas at constant volume and amount. As temperature increases, pressure increases.

• Gay-Lussac’s Law Equation: $\frac{P_1}{T_1} = \frac{P_2}{T_2}$

• Application: Used to calculate unknown temperature or pressure.

• Example: A sealed container’s pressure rises as it is heated.

Section 8.5: The Combined Gas Law

The combined gas law incorporates Boyle’s, Charles’s, and Gay-Lussac’s laws to relate pressure, volume, and temperature when the amount of gas is constant.

• Combined Gas Law Equation: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$

• Application: Used when two properties change and the amount of gas remains constant.

• Example: Calculating the new volume of a gas when both pressure and temperature change.

Chapter 9: Solutions

Section 9.1: Solutions

A solution is a homogeneous mixture of two or more substances. The substance present in the greatest amount is the solvent, and the substance(s) present in lesser amounts are solutes.

• Solute: The substance dissolved in the solvent.

• Solvent: The substance in which the solute is dissolved.

• Formation: Solutions form when solute particles disperse uniformly throughout the solvent.

• Example: Salt (solute) dissolved in water (solvent).

Section 9.2: Electrolytes and Nonelectrolytes

Solutes can be classified as electrolytes or nonelectrolytes based on their ability to conduct electricity when dissolved in water.

• Electrolytes: Substances that dissociate into ions in solution and conduct electricity (e.g., NaCl).

• Nonelectrolytes: Substances that do not dissociate into ions and do not conduct electricity (e.g., sugar).

• Identification: Ionic compounds are typically electrolytes; molecular compounds are often nonelectrolytes.

Section 9.3: Solubility

Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.

• Unsaturated Solution: Contains less solute than the maximum possible; more solute can dissolve.

• Saturated Solution: Contains the maximum amount of solute; no more can dissolve.

• Temperature Effects:

  • Solubility of solids and liquids generally increases with temperature.

  • Solubility of gases decreases with increasing temperature.

• Solubility Table: Used to determine if an ionic compound is soluble or insoluble in water.

• Example: Table salt (NaCl) is soluble; calcium carbonate (CaCO3) is insoluble.

Section 9.4: Solution Concentration

Concentration expresses the amount of solute in a given amount of solution. Common units include mass percent, volume percent, mass/volume percent, and molarity.

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

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

• Mass/Volume Percent: $\text{Mass/Volume percent} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100\%$

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

• Application: Concentration can be used as a conversion factor to calculate the amount of solute or solution.

• Example: A 0.5 M NaCl solution contains 0.5 moles of NaCl per liter.

Section 9.5: Dilution of Solutions

Dilution involves adding more solvent to a solution, decreasing its concentration without changing the amount of solute.

• Dilution Equation: $C_1 V_1 = C_2 V_2$

• Application: Used to calculate unknown concentration or volume after dilution.

• Example: To prepare 250 mL of 0.1 M solution from a 1.0 M stock, use $V_1 = \frac{C_2 V_2}{C_1}$.