Chemistry S2 - States of Matter and Gas Laws

Solids

• have definite(fixed) shape and definite volume

• have strong IMFs holding them together in rigid structure

• do not flow, instead particles vibrate in place.

Liquids

• have definite volume, do not have definite shape

• have intermediate IMFs holding them together

• can flow, particles move and slide past one another

Gases

• do not have definite shape and do not have definite volume

• have weak IMFs - not held together at all

• can flow, the particles move around independently from one another

Liquid —> Gas

Boiling/Condensing

Solid —> Liquid

Melting/Freezing

Solid —> Gas

Sublimation/Deposition

Kinetic Energy

the energy of motion; directly proportional to temperature of substance.

Temperature

the measure of an object’s average kinetic energy (KE); all items at same temperature have same KE

Kelvin Scale

the unit of temperature that directly measures the amount of KE

Assumptions of Kinetic Energy for Gases

• gas particles are small spheres w/insignificant volume

• gas particles move rapidly in constant random motion

• all collisions are perfectly elastic

• there is no attraction/repulsion between particles

Gas Pressure

the force exerted by a gas per unit of surface area; caused by millions of collisions of gas particles w/the side of the container

How is pressure inside a closed container measured?

using a manometer whether liquid or gas. atmospheric pressure is measured using a barometer (used in forecasting).

Vaporization

the process of a liquid becoming a gas either through evaporation(occurs at surface of liquid at any temp) or boiling(occurs throughout liquid when liquid reaches boiling point)

Evaporation

• occurs at surface of liquid

• particles w/enough KE to break attractive forces holding liquid together become a gas

• overall KE of liquid decreases, making evaporation a cooling process

Vapor Pressure

• in closed container, evaporation only proceeds to certain point

• pressure of gas trapped above liquid (vapor pressure)

• vapor pressure increases w/increasing temp

• more evaporation = higher vapor pressure

Boiling Point

• heat liquid —> more particles able to leave surface —> increases vapor pressure

• when liquid heated high enough so that vapor pressure = external/atmospheric pressure (boiling), because of this you can change the bp of liquid by changing pressure liquid is under

• occurs throughout liquid, not just at surface

• normal bp - the temp at which liquid boils at 1 atm

The Gas Laws

mathematical relationships that can be used to predict changes to gaseous bodies dealing w/pressure, temperature, volume and amount (moles) all relating to Kinetic Theory of Gases

Boyle’s Law

• P₁ x V₁ = P₂ x V₂

• determined relationship between a gas’s pressure & volume was inversely related (as 1 increases the other decreases)

• only when temperature & amount of gas is held constant

Charles’ Law

• V₁/T₁ = V₂/T₂

• discovered the relationship between a gas’s volume & temp are directly related (as 1 increases the other will as well)

• only if amount & pressure held constant

Gay-Lussac’s Law

• P₁/T₁ = P₂/T₂

• discovered the relationship between a gas’s pressure & temp are directly related (as 1 increases the other will as well)

• only if amount & pressure held constant

Avogadro’s Law

• V₁/n₁ = V₂/n₂

• if 2 samples of a gas at STP have same volume, they contain same number of moles

• the relationship between a gas’s volume & number of particles (moles) are directly related (as 1 increases the other will as well)

• only if temp & pressure are held constant

The Combined Gas Law

• P₁V₁/n₁T₁ = P₂V₂/n₂T₂

• takes all the laws and mashes them into 1 equation

• used whenever a gas is changing in some way, ignore any variables that don’t change

Ideal Gases

• R = PV/nT

• have atoms that take up negligible space

• don’t have IMFs/attractions

• move randomly & have perfectly elastic collisions

• most gases considered ideal at STP; at very low temps or very high pressures gases are not ideal

• for ideal gases the Combined Gas Law always = same amount - Ideal Gas Constant (R)

Ideal Gas Law

• PV = nRT

• use when you have an ideal gas (close to STP) and no change in any variables

Dalton’s Law of Partial Pressure

• P_total = P₁ + P₂ + P₃ + …

• a mixture of gases, the total pressure of system = to sum of partial pressures of each of the individual gases

Diffusion

gas particles moving from high concentration to low concentration ex. perfume moving throughout the room

Effusion

gas particles moving from high pressure to low pressure ex. particles coming out of a hole in a tire

Graham’s Law

• r1/r2 = r₁/r₂ = √M₂/M₁

• states rate of diffusion/effusion of gas is inversely proportional to molecular weight - heavy gases move slow, light gases move quick

Vapor Pressure Curves

• show the relationship of a liquid’s boiling point (temp) to its vapor pressure

• as you increase temp, vapor pressure of liquid will increase

• vapor pressure = atmospheric pressure, liquid will boil

Phase Diagram

• a graph of pressure as a function of temperature

• shows all 3 states of matter

• triple point: the pressure & temp at which all 3 states of matter exist simultaneously