Chapter 5 Gases Vocabulary

Gases are composed of small particles moving rapidly in straight lines with negligible attractive or repulsive forces. These particles are very far apart, possessing very small volumes relative to their container and kinetic energies that increase with temperature.

The volume of a gas matches its container's volume, typically measured in liters or milliliters. Gas temperature, measured in Kelvin, relates to the average kinetic energy of the molecules; decreasing temperature reduces molecular collisions, while increasing temperature increases them. Pressure measures the collisions of gas particles with the container's sides, quantified in units such as mmHg, torr, atm, Pa, kPa, and psi. Atmospheric pressure is exerted by air particles.

Gases are described by pressure (P), volume (V), temperature (T), and amount (n). The SI unit for pressure is Newton/meter^2, equivalent to 1 Pascal (Pa). Standard atmospheric pressure is 101,325 Pa, 101.325 kPa, or 1.01325 bars, and also equals 1 atm, 760 mmHg, or 760 torr. Pressure is defined as force per area. A barometer measures atmospheric pressure as the height of a mercury column, with 760 mmHg = 1 atm = 760 torr. Evangelista Torricelli invented the barometer. Atmospheric pressure, the pressure exerted by a column of air, is 1 atm at sea level and varies with weather and altitude; rising mercury indicates higher pressure on sunny days, while falling mercury indicates lower pressure on rainy days.

For example, converting 2.5 atm yields 1.9 \times 10^3 torr and 2.5 \times 10^5 Pa. Boyle's Law states that gas pressure is inversely related to volume at constant temperature, expressed as P \times V = constant. Decreasing volume increases pressure, following the formula P1V1 = P2V2. Charles's Law indicates that gas volume is directly related to Kelvin temperature at constant pressure and moles, described by \frac{V1}{T1} = \frac{V2}{T2}. This can be rearranged to solve for V2 or T2. Gay-Lussac's Law states that gas pressure is directly related to Kelvin temperature at constant volume and amount of gas. The relationship is expressed as \frac{P1}{T1} = \frac{P2}{T2}, which can be solved for P*2.

The Combined Gas Law integrates Boyle’s, Charles’s, and Gay-Lussac’s laws, showing the relationship \frac{P1V1}{T1} = \frac{P2V2}{T2} where n is constant. Avogadro's Law states that gas volume is directly related to the number of moles (n) at constant T and P, given by \frac{V1}{n1} = \frac{V2}{n2}. Standard Temperature and Pressure (STP) conditions are 0ºC (273 K) and 1 atm (760 mmHg). The molar volume at STP is 22.4 L per mole of gas.

The Ideal Gas Law is represented as PV = nRT, where R is the ideal gas constant (0.0821 L atm / (mol K)). In gas stoichiometry, 1 mol of gas equals 22.4 L at 1 atm and 273 K. The molar mass of a gas can be calculated using Molar\ mass = \frac{dRT}{P}, where d is the density. Dalton's Law of Partial Pressures states that the total pressure of a gas mixture is the sum of each gas's individual pressure, expressed as P{Total} = P*1 + P2 + ….

The Kinetic Molecular Theory of Gases includes postulates such as negligible particle volume, constant particle motion (causing pressure), no inter-particle forces, and average kinetic energy being directly proportional to Kelvin temperature. Effusion is the passage of gas through a tiny orifice, while diffusion is the mixing of gases. Graham’s Law of Effusion states that the rate of effusion is inversely proportional to the square root of molar mass. Real gases deviate from ideal behavior at high pressures and low temperatures due to high particle concentration and significant attractive forces, which are corrected using Van der Waals forces.

Atmospheric chemistry involves air pollution from transportation and electricity production. Combustion of petroleum produces various gases. At high temperatures, nitrogen and oxygen form NO2, which decomposes into NO and oxygen atoms, leading to ozone (O3) formation. Sulfur produces SO2 when burned, which oxidizes into SO3 and combines with rainwater to form sulfuric acid.