Loveland High School Mrs. Partridge Gas Laws Loveland High School Mrs. Partridge

Kinetic Molecular Theory Kinetic molecular theory of gases uses the behavior of individual molecules to account for the physical properties and gas laws.

Theory Gases are made up of particles that are constantly moving in a straight line. Gases are mostly empty space - the distance between the particles is great. There are no attractive forces between particles (move independently). Particles collide with each other and the walls of their container without incurring a loss of energy. The average kinetic energy is directly proportional to the absolute temperature (increase temp.: increase speed).

Properties Gases can be compressed easily. Gases expand to fill the volume of their container. Gases have low densities. Gases can diffuse through each other. Gases exert a pressure on container walls.

Measuring Gas Pressure A barometer is a device to measure atmospheric pressure Consists of a sealed column containing Hg Measures pressure by allowing air to exert a force against the Hg – which exerts a force back 1 atm of atmospheric pressure will support a column of 760 mm Hg

Measuring Gas Pressure Closed ended monometer – a device to measure pressure of gases other than the atmosphere A U-tube containing Hg is connected to a flask containing the gas in question Gas molecules moving within the flask exert force on the Hg The difference in height of Hg in the U-tube is used to determine the gas pressure.

Dalton’s: Combined Pressure Particles move independently of each other, each gas in a mixture exerts a pressure (P) of its own. The TOTAL pressure (PT) will be the sum of the individual pressures.

Dalton’s: Combined Pressure

Boyles: Volume & Pressure When volume (V) decreases, the particles collide with wall more, leading to greater pressure (P). INDIRECT RELATIONSHIP!

Boyles: Volume & Pressure

Boyles: Volume & Pressure

Charles: Volume & Temperature When temperature (T) increases, particles have more kinetic energy and travel faster - colliding harder with the walls and with other particles. Pressure (P) increases until the volume (V) expands to the point where the pressure (P) inside the walls is again equal to the pressure outside. Volume and Temperature have a DIRECT RELATIONSHIP!

Charles: Volume & Temperature

Charles: Volume & Temperature

P1V1 / T1 = P2V2 / T2 Combined Gas Law: Accounting for the relationship from the first three laws we can combine them into: P1V1 / T1 = P2V2 / T2

Gay-Lassac’s Law: Pressure & Temperature As temperature increases the particles gain more kinetic energy, move more rapidly, collide more often therefore the pressure will increase. Combined gas: P1V1 /T1 = P2V2 / T2 If the Volume is kept constant, it would appear the same on both sides of the equation and could be eliminated: so, P1 / T1 = P2 / T2 Consequently there is a DIRECT RELATIONSHIP between T and P.

Graham’s Law: velocity of diffusion & molecular mass Particles with greater molecular mass will diffuse at a slower rate than those with less mass. A ratio can be calculated as follows:

Graham’s Law: velocity of diffusion & molecular mass     Graham's Law-- The rate of diffusion is inversely proportional to the square root of the molecular mass. Heavy molecules diffuse more slowly.

Avogadro’s Law: Volume & Moles For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles (n) of gas. V1 / n1 = V2 / n2 if temperature and pressure remain constant. Equal numbers of gas particles at the same T & P have the same volume. When the # of moles of gas is doubled, the volume also doubles. DIRECT RELATIONSHIP

Avogadro’s Law: Volume & Moles

Avogadro’s Law: Volume & Moles

The Ideal Gas Law Boyle’s law, Charles’s law, and Avogadro’s law describe the behavior of gases. The relationship between them show how the V of a gas depends on P, T, and n. PV = nRT, where R is the universal gas constant = 0.0821 L•atm/K•mol

The Ideal Gas Law This gas law involves all the important characteristics of a gas: P, V, n, and T. Knowledge of any three of these properties is enough to define completely the condition of the gas, because the fourth can then be determined.

Summary: Boyle’s P1 V1= P2 V2 Charles’s V1 / T1= V2 / T2 Combined P1 V1 / T1 = P2 V2 / T2 Gay-Lassac’s P1 / T1 = P2 / T2 Dalton’s PT = P1 + P2 + . . . . . . Avagadro’s V1 / n1 = V2 / n2 Graham’s v1 / v2 = √m2 / m1 Ideal PV = nRT