AP Chemistry - Unit 3BC

Kinetic Molecular Theory

Kinetic Molecular Theory

• A gas consists of particles in constant, random motion.

• The combined volume of the particles is negligible compared to the total volume in which the gas is contained.

• The particles exert no attractive or repulsive forces on each other EXCEPT when they collide.

• Collisions between particles are completely elastic.

• The average kinetic energy of the particles is proportional to the Kelvin temperature.

• KE = ½mv²

Gas Law Conversions

• 1000mL = 1L

• K = C + 273

• 1 atm = 760 mmHg = 760 torr = 101.3 KPa

Standard Temperature and Pressure (STP)

• T = 0°C or 273K

• P = 1 atm or 101.3KPa or 760 torr or 760 mmHg

Mole Fraction Equations

• P_A = X_A * P_total

• P_A/P_{total =}X_A

Root mean square speed equation

• u_rms =√3RT/MM

  • R = 8.314 J

• Most probable speed bc the longer tail pulls the average speed slightly to the right

• Boltzmann graphs - distribution of molecular speeds & changing the temperature affects the SHAPE of the curve NOT the area beneath it

Effusion

• Tendency of gas molecules to move through a tiny hole

• rate of ef₁ / rate of ef₂ = √MM₂ / MM₁

Solute

What IS dissolved (lesser concentration)

Solvent

What DOES the dissolving (greater concentration)

Solubility

• “Like dissolves like”

• Ionic compounds tend to dissolve in polar solvents because they form ion-dipoles

Saturated solution

maximum amount of solute dissolved for that temperature and pressure

Unsaturated solution

less than maximum amount of solute is dissolved

Supersaturated solution

temporarily holds more than maximum solute

Molarity equation

M = mol/L

Dilution equation

M₁V₁ = M₂V₂

Particulate models

• Anions are LARGER than cations.

• Opposite forces must be next to each other

Chromatography

• Separates things based on IMFs

• The more polar a component is, the farther it’ll travel

• The less polar, the less it’ll travel

Distillation

• Higher vapor pressure → lower boiling point → weaker IMFs

• Distillate - the liquid coming out of the condensation tube

Microwave radiation

• Molecular rotation (causes molecules to rotate)

• Used to determine composition and structure of compounds

Infrared radiation

• Molecular vibration (causes bonds to vibrate, bend, stretch)

• Higher frequency and shorter wavelengths than microwaves

Ultraviolet and visible radiation

• Transitions in electronic energy levels

• UV is more energetic = UV has higher energy

Wavelength equation

c = λv

Photon energy equation

E = hv

Beer-Lambert Law

• Linear relationship between absorbance and concentration

• A = bc