Chem Lecture 5

Front 1

phase

Back 1

a part of a system that is uniform throughout in respect to chem comp and physical state

usually only one gas phase

Front 2

heat capacity

Back 2

C
q=C x change in T
specific heat capacity: q=mcAT (A is change in...)

measure of energy change needed to change the temperature of a substance

for any substance there are 2 Cs: Cv (constant volume) and Cp (constant pressure)

Cp is greater than Cv - need to put some of the energy using to change temp into changing the size of container/into Work on the surroundings (or in solids, lots E goes into small changes in intermolec F)

Front 3

specific heat capacity of water

Back 3

c = 1 cal g-1 *C-1

Front 4

Calorimeters

Back 4

device that measures E change

constant pressure calorimeter (eg coffee cup calorimeter) - measure E change at atmospheric pressure; measures heats of reaction (at constant P, q= change in H) - use q=mcAT

bomb calorimeter - E change at constant volume therefore the internal E change of rxn (q = change in U); use q=CAT (heat capacity of container)

Front 5

Phase changes

Back 5

arise from changes in the manner in which internal energy is distributed over molecules and space = may result when E of each molec is increased or decreased, or when space around each molec is changed

at bp and mp, energy going in at that temp is to BREAK bonds; after phase change, temp starts to rise again

E that needs to go in to break bonds = heat of fusion (melting) and heat of vaporization (boiling)
** state f'n, same each way

each phase of substance has its own specific heat
slope = 1/mc on heating curve

Front 6

triple point

Back 6

the one point on a phase diagram where a substance can exist in equilibrium as a solid, liquid and gas

Front 7

critical temperature

Back 7

temperature above which a substance cannot be liquefied regardless of pressure applied

pressure required to produce liquefactaion while substance is at critical temperature = critical pressure

together = critical point

Front 8

critical point

Back 8

critical pressure and critical temperature points

fluid beyond has characteristics of both gas and liquid (supercritical fluid)

Front 9

colligative properties

Back 9

properties that depend solely on the number of particles, irrespective of type of particle

vapor pressure
boiling point
freezing point
osmotic pressure

Front 10

boiling point elevation

Back 10

the addition of a nonvolatile solute lowers the vapor pressure and elevates the boiling point

change in bp = kb x m x i
kb is constant of substance being boiled
m = molality
i = van't Hoff factor (number of particles into which a single solute particle will dissociate when added to a soln)

Front 11

Freezing point depression

Back 11

impurities interrupt the crystal lattice and lower the freezing point

change in T= kf x m x i
kf is constant specific to substance being frozen
m - molality
i - van't Hoff factor (number of particles a single solute particle will dissociate when added to soln)

** note - impurities will initially lower melting poing - until so much solute that it is what is main item freezing and adding additional solute acts to reduce the impurities (solvent...) so freezing pt will rise

Front 12

osmotic pressure

Back 12

measure of tendency of water (or other solvent) to move into a solution via osmosis. ONLY relevant when comparing one solution to another

extra pressure on solution side... PULLING PRESSURE (vs hydrostatic P = Pushing P)

osmotic P = i M R T
M is molarity