Chem 5

Front 1

Phases

Back 1

-all intensive macroscopic properties of a system are constant then it is homogenous or in the same phase
-generally there is solid liquid and gas but there can be different forms of solid and liquid forms, aqueous is different from pure etc.
-to change phase you need a change in internal energy

Front 2

Heat Capacity

Back 2

-measure of energy change needed to change the temperature of a substance by 1 degree

q= C(ΔT)

-Cp if at constant pressure something is allowed to expand then some heat can be converted to work and there will be less temperature change
-at constant volume there is no PV work so all heat is converted into temperature change
-Cp is greater than Cv, it takes more heat to change something at constant pressure compared to constant volume by the same amount of temperature
-always positive on the MCAT, temp will always increase with energy added

Front 3

specific heat capacity

Back 3

-heat capacity per unit mass
q=mc(ΔT) m=mass

h20: 1calg-1C-1
4.18 Jg-1C-1
use units for c to determine necessary units of M

Front 4

CALORIMETERS

Back 4

measures energy change
-two types:
constant volume: coffee cup calorimeter
constant pressure: bomb calorimeter

Front 5

coffee cup calorimeter

Back 5

-calorimeter at constant pressure
-at constant pressure q=DeltaH
or enthalpy
measures heats of reactions

Front 6

bomb calorimeter

Back 6

measures energy change at constant volume
-tells internal energy U change because at constant volume q= U no PV work
use q=C(ΔT)to deduce deltaU

Front 7

Phase Changes

Back 7

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slanted lines represent where in a phase temperature is changing: use q=mcΔT, slope=1/mc

straight lines represent phase changes: where q=enthalpy because pressure is constant

Front 8

Phase changes, enthalpy and entropy

Back 8

-enthalpy is state function so amounts necessary for heat transfer during melting or freezing or boiling/condensation are equal

-each phase has its own specific heat

-sublimation-deposition
vaporization/condensation
melting/freezing

-melting and boiling are endothermic, entropy and enthalpy are positive

-freezing and condensation are exothermic, enthalpy and entropy are negative
-during phase changes at constant pressure temperature depends on which way reaction will go

Front 9

phase diagrams

Back 9

-pressure vs. temperature
-lines outlining phases represent dynamic equillibrium
-point where all three lines intersect and a substance is in equillibrium in solid liquid and gas phase is triple point

Front 10

critical point

Back 10

critical temperature:temperature in a phase diagram for which a substance cannot be liquefied regardless of pressure

critical pressure: pressure required to produce liquefacation while substance is at critical temp

-critical point, combination of two,

endpoint of equillibrium line between gas and liquid

Front 11

supercritical fluid

Back 11

-fluid that has characteristics of both liquids and gas

Front 12

H20 vs CO2 phase diagrams

Back 12

-are able to estimate where 1ATM is on these graphs
-since h20 exists as all three phases at 1atm, it is below triple point
-since CO2 sublimates from solid to gas it must be below triple point
-the equilibrium line between liquid and solid in H20 graph has a negative slope bc ice is less dense then water and volume decreases with increasing pressure

Front 13

Colligative properties

Back 13

properties in chemistry that depend on quantity solely, not type
For solutions: vapor pressure, boiling point, freezing point, osmotic pressure

Front 14

Boiling

Back 14

a substance boils when vapor pressure=atm pressure

Front 15

Nonvolatile solutes and boiling points

Back 15

-addition of nonvolatile solute lowers the vapor pressure and elevates the boiling point
-boiling point of ideally dilute solution is equation
: ΔT=Kbx m x i
where kb is a specific constant of the substance being boiled

m is molality (moles solute/kg solvent)

i= van hoff factor (# of particles expected to dissociate from a single particle when added to solution) ex: MgCl2 = 3

-cant apply to volatile solutes bc these increase vapor pressuer and decrease boiling points
-if you know heat of solution then you can guess about boiling point effects :endothermic-weaker bonds-higher vapor pressure-lower boiling point...viceversa

Front 16

Freezing point depression

Back 16

-impurities (solute) interrupt crystal lattice and lower freezing point

ΔT=kf(m)(i)

-if add a liquid solute melting point will lower melting point but when mole fraction increases and solute is being prevented from melting by solvent then it will rise as more solute as added...down then up with increased solute concentration

Front 17

osmotic pressure

Back 17

measure of tendency of water to move into a solution via osmosis

-ex. a pipe with a semipermeable membrane in the middle, on one side is solute, on other side is water, water can diffuse through membrane but not solute,

water diffuses through membrane to increase entropy and solution level rises and pressure increases as P=ρgh and water level or h increases...additional pressure on solute side is osmotic pressure

Front 18

osmotic pressure equation

Back 18

π = iMRT

osmotic pressure= Molarity x Temperature x vant hoff factor x Universal gas constant R = 0.08206 L · atm · mol-1 · K-1

Front 19

Lecture Question 113
Which of the following will have the lowest boiling point?
.5M glucose
1M glucose
.5M NaCl
.6M NaCl

Back 19

Want lower concentration .5, want glucose because it is not ionic it wont dissociate and i=1

Front 20

Lecture question 114:
An object experiences a greater buoyant force in seawater than in freshwater: why?

Back 20

This is because seawater has extra salt but not extra mass so it has more density..

Fb=ρgh

Front 21

Lecture question 117:

Back 21

If the height in the solution tube of an osmotic pressure is greater, that means the osmotic pressure of the solution is high and low for pure water which means it has proportionally a greater molarity and low molecular weight.

Front 22

If you put the same amounts of NaCl and KF into water how will the boiling points of each solution compare?

Back 22

They will be the same. Boiling point is a colligative property. KF and NaCl dissociate into the same amount of ions.