Chapter 10: Physical Characteristics of Gases

The Kinetic Molecular Theory (KMT) describes the behavior of an “ideal” gas. Ideal gases include the noble gases and diatomic gases Real gases deviate slightly from the KMT. At high pressures and low temperatures, deviation may be significant because particles begin to condense into liquid.

KMT Postulates: 1. Gases consist of tiny particles that are very far apart. 2. Gas particles are in constant straight-line motion. 3. The rate of motion of a gas depends on temperature. 4. Collisions between particles and between particles and container walls are elastic. (no loss of energy) 5. Attractive and Repulsive forces do not exist between molecules.

Characteristics of Gases 1. Expansion and Compressibility gases fill containers of any size 2. Low Density small number of particles in a given space 3. Fluidity particles slide past each other 4. Ability to Diffuse and Effuse diffusion –able to spread out and mix with other gases effusion –able to fit through narrow openings

Volume (V) Describing Gases measured in mL or L. (cm3 or dm3) amount of space occupied by a gas at a specific temperature and pressure. measured in mL or L. (cm3 or dm3) 1000 mL = 1 L or 1000 cm3 = 1 dm3

Temperature (T) Average kinetic energy of particles Measured in Kelvin K = °C + 273 Pressure (P) Force exerted over a given area Measured in atm, kPa, mmHg (torr) 1 atm = 101.325 kPa = 760 mmHg (torr)

Standard Temperature and Pressure Special Condition: Standard Temperature and Pressure “STP” 0 °C and 1 atm (273 K) (101.325 kPa) (760 mmHg)

Examples for Converting Units: 275 mL = ? L 0.055 L = ? mL 35 C = ? K 300 K = ? C 1.15 atm = ? mmHg 758 torr = ? kPa

The Gas Laws Boyle’s Law P1V1 = P2V2 animation Pressure and Volume of a gas are inversely proportional. Temperature of gas must remain constant.

Charles’ Law V1 = V2 T1 T2 animation Temperature and Volume of a gas are directly proportional. Pressure of gas must remain constant. Temperature MUST be measured in Kelvin.

Gay-Lussac’s Law P1 = P2 T1 T2 Temperature and Pressure of a gas are directly proportional. Volume of gas must remain constant. Temperature MUST be measured in Kelvin.

Combines 1st three gas laws into one equation. Combined Gas Law P1V1 = P2V2 T1 T2 Combines 1st three gas laws into one equation. Temperature MUST be measured in Kelvin.

Dalton’s Law of Partial Pressures Pmixture = PA + PB + PC + … The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas in the mixture. Pbar = Pgas + PH2O For gases that are collected by water displacement, the sum of the partial pressure of the gas and the vapor pressure of water is equal to barometric pressure.

Gas Law Problem-Solving Examples: 1. A sample of O2(g) has a volume of 150. mL when its pressure is 0.947 atm. What will the volume be when the pressure is increased to 0.987 atm? 2. A sample of Ne(g) has a volume of 752 mL at 25°C. At what Temperature will the volume be 900.mL?

3. A sample of Cl2(g) has a pressure of 100. 5 kPa at 30°C 3. A sample of Cl2(g) has a pressure of 100.5 kPa at 30°C. At what temperature will the gas be at standard pressure? 4. A gas occupies 1.8 L at 300. K and 738 torr. What will be the volume when the temperature is 325 K and pressure is 750. torr?

5. The pressure of a mixture of gases is measured as 2. 58 atm 5. The pressure of a mixture of gases is measured as 2.58 atm. If the mixture is composed of gas A (1.21 atm) and gas B (0.96 atm), what is the partial pressure of gas C? 6. A gas is collected over water with barometric pressure measuring 0.988 atm. The vapor pressure of the water is 17.5 mmHg. What is the pressure of the gas collected, in mmHg?