chem: unit 5 - imfs + state of matter

solid molecules - features

• Molecules are really close together

• Has a definite volume

• Does NOT take the shape of its container

• Cannot be compressed

• Cannot flow

• Lowest energy of the three states we discuss

liquid molecules - features

• Molecules are pretty close together

• Has a definite volume

• Takes the shape of its container

• Cannot be compressed

• Can flow and move readily

• Middle energy of the three states we discuss

gas molecules - features

• Molecules are not very close together

• Does NOT have a definite volume

• Takes the shape of its container

• CAN be compressed

• Can flow and move readily

• Highest energy of the three states we discuss

gas to liquid

condensation

liquid to gas

vaporization

gas to solid

deposition

solid to gas

sublimation

solid to liquid

melting

liquid to solid

freezing

if the temperature doesn’t increase during a phase change, where does the energy go?

the energy is used to break the IMFs between the molecules

when the phase is changing on a heating curve…

potential energy is increasing

when the temperature is changing on a heating curve…

the kinetic energy is increasing

temperature is the…

average kinetic energy of a substance

phase change diagram

a diagram that shows changes in temperature and pressure

triple point

temperature and pressure at which all 3 phases exist together at equillibrium

critical point

temperature and pressure at which two phases become indistinguishable from one another

intermolecular forces (IMFs)

weak force attractions between covalently bonded things

keep molecules of a substance together

weaker than covalent and ionic bonds

london dispersion forces

• really weak forces that result from temporary shifts in density of electrons in electron cloud

• result of temporary dipole (electrons end up on one side of molecule)

• all molecules

• only IMFs nonpolar molecules can have

• more electrons = greater dispersion forces + greater attraction

dipole-dipole forces

• oppositely-charged ends of polar molecules attract, forming dipole-dipole forces

• stronger than dispersion foces b/c dipoles are permanent in polar molecules

• all polar molecules

hydrogen bonds

• special type of dipole-dipole attraction

• hydrogen bonds with O, F, or N (highly electronegative molecules)

strong IMFs correlate to what strength of physical properties?

boiling/melting point - high

surface tension - high

visosity - high

vapor pressure - low

weak IMFs correlate to what strength of physical properties?

boiling/melting point - low

surface tension - low

visosity - low

vapor pressure - high

vapor pressure

created by gas molecules hanging over the surface of a liquid

collision of molecules causes vapor pressure

a substance boils when vapor pressure is equal to atmospheric pressure

high VP: low BP, weak IMFs

low VP: high BP, strong IMFs

molality (m)

moles of solute/kg of solvent

colligative properties

properties that are dependent on the concentration of solute particles instead of their identity

boiling-point elevation

• when you add solute particles to a solution, the boiling point will change

• change in temp = bp constant (Kb) * molality of solute (m) * van’t hoffs of solute (i)

freezing-point depression

• as you add solute particles to a solute particles to a solution, the freezing point goes down

• change in temp = -freezing point constant * molality of solute * van’t hoffs of solute

van’t hoff factor (i)

• only have to worry about ionic substances

• depends on how many ions it breaks into

how to convert to moles

step #1: find molar mass of substance

step #2: dimensional analysis: multiple the amount of substance you have by the conversion factor of 1 mol/molar mass of substance

why are gases special?

• all have very similar physical properties/can be easily predicted

• we can use generalized laws and one comprehensive theory to explain most behaviors of gases.

how are pressure and volume related?

• pressure and volume of a gas are inversely related

• as one increases the other decreases

• boyle’s law: P1V1 = P2V2

how are temperature and volume related?

• temperature and volume are directly related

• as one increases the other increases

• charles’ law: V1/T1 = V2/T2

how are temperature and pressure related?

• pressure and temperature are directly related

• as one increases the other increases.

• gay lussac’s law: P1/T1 = P2/T2

how are volume and # of moles related?

• volume and number of moles (n) are directly related

• avogadro’s law: V1/n1 = V2/n2

ideal gas law

PV = nRT

kinetic molecular theory

• Gas particles move in continuous, random motion in straight lines until they collide with something (another particle or the container).

• The actual volume of individual gas particles is so small compared to the total volume of the gas that it is considered negligible.

• IMFs in gas are so weak that we can just ignore them

• When gas particles collide with each other or the container, no kinetic energy is lost

• The average kinetic energy of gas particles is directly proportional to the temperature (in Kelvin). Higher temperatures mean faster-moving particles.

real gases vs ideal gases

real gases:

• do have volume

• do have IMFs

how is a gas more ideal than another?

• Low Pressure (more empty space between molecules)

• High Temperature (More energy to overcome IMFs)

• Weaker Forms of Intermolecular Forces (such as LDF)

• Lower Molecular Mass (Fewer Electrons)