Chem Chapter 5

Pressure

collisions of gas particles (force/area)

atmospheric pressure

the pressure exerted by Earth’s atmosphere

air pressure

altitude - higher you are the less pressure

intermolecular forces (IMF)

determines an elements state of matter

STP

standard pressure and temperature (temp: 0 deg. C, 273K; pressure: sea level most commonly 1 atm)

barometer

instrument for measuring atmospheric pressure

manometer

a device is used to measure the pressure of gases other than the atmosphere

Boyle’s Law

P&V - the pressure of a fixed amount of gas at a constant temperature is inversely proportional to the volume of the gas

Equation: p1v1=p2v2

Charles’ Law

the volume of a fixed amount of gas maintained at constant pressure is directly proportional to the absolute temperature of the gas

Equation: v1/t1 = v2/t2

absolute zero

theoretically the lowest attainable temperature

Kelvin temperature scale

absolute temperature scale with absolute zero as the starting point (C = K - 273)

Gay-Lussac’s Law

the pressure of a fixed amount of gas maintained at constant volume is directly proportional to the absolute temperature of the gas

Equation: p1/t1 = p2/t2

Avagadro’s Law

Equation: v1/n1 = v2/n2

Combined gas law

p1v1/n1t1 = p2v2/n2t2

R

ideal gas constant (0.08206)

Ideal Gas Law vs. Combined Gas Law

Ideal: to describe a gas that is not changing

Combined: for a gas that is changing conditions, initial and final conditions are given

ideal gas

a hypothetical gas whose pressure-volume-temperature behavior can be completely accounted for by the ideal gas equation (gases behave ideally in high temp and low pressure, and deviate from ideal vice versa)

density

mass/volume → Pmm/RT

Dalton’s Law of Partial Pressures

the total pressure of a mixture is just the sum of the pressures that each gas would exert if it were present alone

• each gas will behave as if they are the only ones in the container. This allows us to use the mole fraction to determine an individual gas’ partial pressure

partial pressures

the pressures of individual gas components in a mixture of gases

mole fraction

expresses the ratio of the number of moles of one component to the number of moles of all components present

• never expressed as a fraction, always converted to decimal

Collecting gas over water

P_t = P_H2 + P_H2O

Vapor pressure

due to the collisions of the vapor particles that have “escaped” the liquid and are in the gas state above the liquid

• need to know the water temp to use the chart to find the pressure

kinetic energy

energy of motion

Kinetic Molecular theory of gases

• Gases are made of tiny particles that move constantly and randomly.

• They collide with each other and the walls of their container, causing pressure.

• These particles are far apart and have almost no attraction between them.

• The faster they move, the higher the temperature.

Distribution of molecular speeds

whichever molecule is the hottest or lightest is moving the fastest

diffusion

the gradual mixing of molecules of one gas with with molecules of another by virtue of their kinetic properties

Graham’s Law of Diffusion

under the same conditions of temperature and pressure, rates of diffusion for gases are inversely proportional to the square roots of their molar masses

Effusion

the process by which a gas under pressure escapes from one compartment of a container to another by passing through a small opening