Gas Laws Chapter 5

Units of Pressure Kilopascals (SI unit) Millimeters of mercury is the same as a torricelli Atmospheres Pounds per square inch 101.3 kPa = 760 mm Hg (torr) = 1 atm = 14.7 psi

Barometers

Open Manometers

Closed Manometer

Manometer problems

Answers: 1. 727 mm Hg 2. 685 mm Hg 3. 871 mm Hg

Manometer Problems continued

STP Standard Temperature and Pressure Standard Temperature is 0 ˚C or 273 K Standard Pressure is 101.3 kPa Kelvin = ˚Celcius + 273

Boyle’s Law If the temperature remains constant, Pressure and Volume have an inverse relationship P1 x V1 = P2 x V2 Watch for unit agreement!

Charles’ Law If pressure remains constant, then volume and Kelvin temperature will have a direct relationship. V1 = V2 T1 T2 Temperature MUST be in Kelvin…volume needs unit agreement

Gay-Lussac’s Law If the volume of a gas is held constant, then there is a direct relationship between pressure and Kelvin temperature. P1 = P2 T1 T2 Temperature MUST be in Kelvin and unit agreement for pressure

Combined Gas Law P1V1 = P2V2 T1 T2 Make sure you have unit agreement and temperature must be in Kelvin!

PV= nRT Ideal Gas Law P= Pressure V = Volume (in Liters) n = moles R = Gas Constant (8.314 L·kPa/mol·K) T = Temperature in Kelvin

Avogadro’s Law V1 = V2 n1 n2 V = volume n= moles

Dalton’s Law of Partial Pressures For a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone. Ptotal = P1 + P2 + P3 + …

Kinetic Molecular Theory The particles are so small compared to the distances between them that the volume of the individual particles can be assumed to be negligible (zero). The particles are in constant random motion. The collisions of the particles with the walls of the container are the cause of the pressure exerted by the gas. The particles are assumed to exert no forces on each other; they are assumed to neither attract nor repel each other. The average Kinetic energy of a collection of gas particles is assumed to be directly proportional to the Kelvin temperature of the gas.

Real Gases Have finite volumes Do exert forces on each other Van der Waals equations correct for this reality Gases only behave ideally at: High Temperatures and Low Pressures

Meaning of Temperature Kelvin Temperature indicates the average Kinetic energy of the gas particles. (KE) avg = 3/2 RT

Root Mean Square Velocity Average Velocity of the gas particles U rms = √3RT/M

Effusion Effusion is diffusion of a gas through a small opening Rate of Effusion of Gas 1 = urms for gas 1 Rate of Effusion of Gas 2 urms for gas 2