Chemistry - Pressure and Gas

Standard temperature and pressure

0C and 1 atm

Postulates of the Kinetic Molecular Theory

1. The particles are so small compared with the distances between them that the volume of the individual particles can be assumed to be negligible. 2. The particles are in constant motion. The collisions of the particles with the walls of the container are the cause of the pressure exerted by the gas 3. The particles are assumed to exert no forces on each other; they are assumed neither to attract nor to repel each other 4. The average kinetic energy of a collection of gas particles is assumed to be directly proportional to the Kelvin temperature of the gas.

Molar volume

22.42 L in 1 mole - ideal GAS at )C and 1 atm

Molar Volume

22.42 L per moles at STP (0C and 1 atm)

Ideal Gas

A gas that strictly obeys Boyle's law

0K

Absolute Zero

Volume and Number of Moles (Avogadro's Law)

An increase in the number of gas particles at the same temperature would cause the pressure to increase if the volume were held constant. The only way to return the pressure to its original value is to increase the volume

Temperature must always be converted to the Kelvin Scale

C + 273.15 = K

Van der Waals equation

Correction factor for pressure and volume in one equation

Molar Mass = dRT/P

Derived from mRT/PV - mass/volume is density - Only for GAS

Van der Waals

Described the need for a correction factor to modify the assumptions of the kinetic molecular theory to fit the behavior of real gases.

Inverse relationship - multiplication

Direct relationship - Division

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. Total = P1 + P2 + P3 +... Partial pressures calculated through ideal gas law assuming that each gas behaves ideally

Charles's Law

Found that the volume of a gas at constant pressure increases linearly with the temperature of the gas. V = bT The volume of each gas is directly proportional to temperature T = in Kelvin K = C + 273.15 O K is called absolute zero

Gases are most NON-Ideal at their liquefaction condensing point

Gases are most ideal at High temperatures and low pressures

The rate of effusion of a gas is inversely proportional to the square root of the mass of its particles

Graham's Law of effusion

Density

Grams/Liter

Pressure and Volume (Boyle's Law)

KMT connection: This makes sense based on the kinetic molecular theory because a decrease in volume means that the gas particles will hit the wall more often, thus increasing pressure

When gas particles come close together - real gases, attractive forces occur, which causes the particles to hit the wall very slightly less often than they would in the absence of these interactions

KMT goes against this and says that ideal gases show no attractive forces towards each other: "The particles are assumed to exert no forces on each other; they are assumed neither to attract nor to repel each other"

Universal gas constant - remember to label this unit

Liters x arms / K x moles

Water vapor is present because molecules of water escape form the surface of the liquid and collect in the space above the liquid

Molecules of water also return to the liquid

Rearranged

P1 = X1 x Ptotal Partial pressure of a particular component of a gaseous mixture is the mole fraction of that component times the total pressure

Gay Lussac's Law

P1/T1 = P2/T2

Combined gas law

P1V1/T1=P2V2/T2 - MOLES are constant - set equal to the universal gas constant (R)

Boyle's law

PV = k: There is an inverse relationship between pressure and volume

Ideal Gas Law

PV = nRT

Avogadro's Law

Postulated that equal volumes of gases at the same temperature and pressure contain the same number of particles. V=an For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas V1/n1 = V2/n2

Graham's Law of Effusion

Rate of effusion for gas 1/Rate of effusion for gas 2 = square root of Molar Mass of 2 / Molar Mass of 1 Diagonal

Diffusion rates

Related to Molar Mass - NH3 and HCL example with cotton balls

Kinetic Molecular Theory (KMT)

Simple model that attempts to explain the properties of an ideal gas. The model is based on speculations about the behavior of the individual gas particles.

0C and 1atm

Standard Temperature and Pressure

Diffusion

Term used to describe the mixing of gases. The rate of diffusion is the rate of the mixing of gases.

Effusion

Term used to describe the passage of a gas through a tiny orifice into an evacuated chamber. The rate of effusion measures the speed at which the gas is transferred into the chamber.

Pressure and Temperature (Gay Lussac)

The KMT accounts for this behavior because when the temperature of a gas increases, the speeds of its particles increase, the particles hitting the wall with greater force and greater frequency. Since the volume remains the same, this would result in increased gas pressure.

Mixture of Gases (Dalton's Law)

The KMT assumes that all ages particles are independent of each other and that the volumes of the individual particles are unimportant. Thus the identities of the gas particles do not matter.

Mole fraction

The ratio of the number of moles of a given component in a mixture to the total number of moles in the mixture X1= n1/nTotal

U^2 = the average of the squares of the particle velocities

The square root of U^2 is called the root mean square velocity

Charles Law

The volume of each gas is directly proportional to temperature and extrapolates to zero when the temperature is 0K.

Boyles Law

There is an inverse relationship between pressure and volume - P1V1 = P2V2 Ex: As pressure increases, the volume should decrease As pressure decreases, volume should increase

The volume available to a given particle in a real gas is less than the volume of the container because the gas particles themselves take up some of the space.

V (volume of the container) minus a correction factor for the volume of the molecules

Volume and Temperature (Charles's Law)

When the gas is heated to a higher temperature, the speeds of its molecules increase and thus they hit the walls more often and with more force. The only way to keep the pressure constant in this situation is to increase the volume of the container. This compensates for the increased particle speeds.

R = Universal gas constant

When the pressure is expressed in atmospheres and volumes in LITERS, R has the value 0.08206

Vapor pressure of water

When the rate of escape equals the rate of return, the number of water molecules in the vapor state remains constant, and thus the pressure of water vapor remains constant - vapor pressure of water

Mole fraction relates to Pressure in the form of the ideal gas equation

X1 = n1/nTotal = P1/PTotal

Root Mean square velocity

the square root of the average of the squares of the individual velocities of gas particles