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22 Cards in this Set

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Phases
-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
Heat Capacity
-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
specific heat capacity
-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
CALORIMETERS
measures energy change
-two types:
constant volume: coffee cup calorimeter
constant pressure: bomb calorimeter
coffee cup calorimeter
-calorimeter at constant pressure
-at constant pressure q=DeltaH
or enthalpy
measures heats of reactions
bomb calorimeter
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
Phase Changes
_/
___/
/
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
Phase changes, enthalpy and entropy
-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
phase diagrams
-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
critical point
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
supercritical fluid
-fluid that has characteristics of both liquids and gas
H20 vs CO2 phase diagrams
-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
Colligative properties
properties in chemistry that depend on quantity solely, not type
For solutions: vapor pressure, boiling point, freezing point, osmotic pressure
Boiling
a substance boils when vapor pressure=atm pressure
Nonvolatile solutes and boiling points
-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
Freezing point depression
-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
osmotic pressure
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
osmotic pressure equation
π = iMRT

osmotic pressure= Molarity x Temperature x vant hoff factor x Universal gas constant R = 0.08206 L · atm · mol-1 · K-1
Lecture Question 113
Which of the following will have the lowest boiling point?
.5M glucose
1M glucose
.5M NaCl
.6M NaCl
Want lower concentration .5, want glucose because it is not ionic it wont dissociate and i=1
Lecture question 114:
An object experiences a greater buoyant force in seawater than in freshwater: why?
This is because seawater has extra salt but not extra mass so it has more density..

Fb=ρgh
Lecture question 117:
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.
If you put the same amounts of NaCl and KF into water how will the boiling points of each solution compare?
They will be the same. Boiling point is a colligative property. KF and NaCl dissociate into the same amount of ions.