Chemistry Lect 5

any part of a system that is homogenous

a measure of the energy chance needed to change the temp of a substance --> think of it as internal energy capacity

• C: heat capacity
• q: heat
• T: temp

simply the heat capacity per unit mass

q = m c ΔT

• q: heat
• m: mass
• c: specific heat
• T: change in temp

• - measures the Δenergy at atmospheric pressure (∴ a constant pressure system)
• -used to measure heats of a reaction (@ constant pressure q=ΔH)

• i.e. we mix H⁺ + OH^- --> H₂O
• we can solve for "q" in q=mcΔT and since @ const. P, q=ΔH, we have the heat of the rxn

• - measures Δenergy at constant volume
• - used to measure internal energy change (@ constant volume q=ΔU)

i.e. use known heat capacity (C) of the container and the q=CΔT to deduce the internal energy (U)

• (1) Melting - Freezing
• (2) Vaporization - Condensation
• (3) Sublimation - Deposition

when the partial pressure above the liquid is less than (<) the vapour pressure of the liquid

BUT atmospheric P. > vapour P.

*this allows the liquid to evaporate rather than boil

Atmos. P = Vapour P. of a liquid

Vapour P_solid = Vapour P_liquid

Exactly the same amount of heat that is absorbed when melting is released when freezing

solid --> liquid (melting)

liquid --> gas (vaporization)

- critical temp: above which a substance cannot be liquified regardless of the pressure applied

- critical pressure: required to produce liquification while the substance is at the critical temp

critical pressure, critical temp = critical pt

There is no change in temperature during a phase change.

Otherwise, energy increases molecular movement which increases temperature.

slope = 1 / mc

• m: mass
• c: specific heat

- properties that depend only on the number of particles and not the type

• (1) vapour pressure
• (2) boiling point
• (3) freezing point
• (4) osmotic pressure

- with the addition of a nonvolatile solute there is a decrease in vapour pressure

- boiling point occurs when V.P. = Atmos. P.

- ∴ when V.P. decreases the b.p. increases

ΔT = k_bmi

• k_b: a constant
• m: molality
• i: # of ions after dissociation
• (i.e. NaCl --> Na + Cl ∴i = 2)
• (i.e. MgCl₂ --> Mg⁺² + 2Cl ∴ i = 2)

• - the addition of a nonvolatile solute can interrupt the crystal lattice
• - this will lower the freezing point

*be careful: eventually you get to a point where the solvent becomes the impurity preventing the solute from freezing --> ∴ the freezing point lowers at first and then rises again after it has hit this point

ΔT = k_fmi

• k_f: a constant
• m: molality
• i: # of ions after dissociation
• (i.e. NaCl --> Na + Cl ∴i = 2)
• (i.e. MgCl₂ --> Mg⁺² + 2Cl ∴ i = 2)

- only relevant when comparing one solution to another

• - think of a selectively permeable membrane
• if one side is concentrated, the water will move to wards that side in order to maintain the same dilution factor

Π = iMRT

• Π: osmotic pressure
• i: # of ions after dissociation
• M: molarity
• T: temp

- this gives you the pressure on one side of the membrane (the total pressure is the difference between both sides)