unit 6: phases i. phases defined and characterized
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Unit 6: Phases
I. Phases Defined and Characterized
a. Substances vs. Mixtures
Substances = element/compound Mixture = various combinations
b. Solids Properties:
Low temperature Low Kinetic energy Slow diffusion rates Strong intermolecular forces Fixed volume and shape
c. Liquids
Properties:Low to medium low temperature (KE)Medium to slow diffusion ratesSomewhat strong IMF’s Volume fixed shape depends on container
d. Gas
High KELow attractive forces between moleculesNo definite shape or volume; depends upon containerParticles spaced far, far apart
Phases Summary Chart
Liquids
Entropy [disorder]Shape,Properties
Energy
GasesSolids
Introducing…..
“Heating and Cooling Curves”
A short video by Mark Rosengarten:
http://www.youtube.com/watch?v=DhZ3r9qp7Ik
II. Heating and Cooling Curves
Phase Changes
Phase Change = changing the state of a substance by altering the temperature and pressure; reversible PHYSICAL CHANGE
Dynamic Equilibrium exists when 2 phases exist together; at temperature and pressure of the phase change
Terms for Phase Changes
1) Evaporation or Vaporization
2) Condensation
3) Fusion
4) Solidification
5) Sublimation
6) Deposition
Concepts for Phase Changes
Energy absorbed to change from lower temp to higher temp substance
Energy released to change from a higher temp to a lower temp
Relate phase changes and terms to Heating/Cooling Curves!Identify: Single Phases
vs.Dynamic Equilibrium
[phase change]
PE vs KE Changes on Heating/Cooling Curves
Changes in KE occur whenever there is a change in TEMPERATURETEMPERATURESections with only 1 phase have KE changes Ex.]
Changes in PE occur during a phase change when the temperature is CONSTANTCONSTANTPhase changes occur on flat sections
Ex.]
Heat of Fusion
Heat of FusionThe amount of heat energy required to convert a substance from a solid into a liquid, or vice versa
For water: Hf = 334 J/g
Equation…
Heat of Vaporization
Heat of Vaporizationthe amount of heat energy required to convert a substance from a liquid into a gas, or vice versa
For water:
Hv = 2260 J/g
Equation…
Relate Hv and Hf to IMF’s
Stronger IMF’s lead to: Higher boiling
points Lower vapor
pressure
Weaker IMF’s lead to: Low boiling points Higher vapor
pressure
IV. Heat Calculations
Three equations are used to calculate heat energy transferred during a heatins/cooling curve: q = mcΔT used during…?
q = mHv used during….?
q = mHf used during….?
Ex.] on board
2. Vaporization and Boiling
Vapor pressure = the pressure exerted by a layer of the gas phase on the surface of a liquid or solid High Vapor pressure = weaker IMF’s,
weaker bonds, changes to gas phase easily
Low vapor pressure = STRONGER IMF’s, stronger bonds, and prefers to remain a liquid phase
Table H Vapor Pressure of Four
Liquids
3. Boiling Point vs. Normal Boiling Point
Boiling Point = temperature at which vapor pressure of the liquid equals the atmospheric pressure of the surroundings
NORMAL boiling point =
temperature when the vapor pressure equals
standard pressure [1atm]
What changes the boiling point?
Changes in atmospheric pressure cause changes in the boiling point
Low pressure at higher altitudes cause the boiling point to be lower than normal [pressure is lower than normal…]
High pressure occurring below sea level cause boiling points to increase […?]
Vapor Pressure… REVIEW…
Vapor pressure changes INDIRECTLYINDIRECTLY with variations is atmospheric pressure Explain……
Vapor pressure is a function of IMF’s within the liquid phase Stronger IMF’s = ________ vapor pressure Weaker IMF’s = _________ vapor pressure
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swf
4. Sublimation and DepositionSublimation Deposition
III. Temperature
Average KE of particles within an areaMeasured in Celsius or Kelvin
K = oC + 273
Potential energy = stored energy; no temperature changes
Changes in KE = changes in Temperature; reflects Energy in motion
V. Gases
PressureUnits and definitions: Torr, atm, mmHg, kPa, Pa, etc. [on
board] Standard Pressure = ………. Use Dimensional Analysis to convert
from one unit to another!
a. KMT
KMT = Kinetic Molecular Theory
Theoretical Model explaining how/why particles behave as they doBased on ideal gas equation: PV=nRTDescribes the behavior of an ‘ideal gas’
A. Postulates [parts]
1- Gas particles move in straight-line, continuous, random motion
2- Have NO attractive forces due to large distances between molecules
3- The volume of the particles themselves are negligible compared to the volume of the gas itself
Postulates cont’.
4- Particles have perfectly elastic collisions
5- Total Kinetic Energy of the system is proportional to the absolute temperature of the system
B. Ideal Gases vs. Real Gases
Ideal Gases:
Have no attractive forces between particles
Particles have no relevant volume
Real Gases:
Have attractive forces between their particles
Particles themselves have a definite volume
The MOST Ideal of the Real Gases are...
Most IDEAL Gases
HydrogenHelium
Why?... Both have very small
volumes Both have very weak
attractive forces
Most IDEAL Conditions
HIGH TemperatureLow Pressure
Why?... Lots of Kinetic energy,
moving very fast so little time for attractive forces
Large volume, lots of space, so little taken up by atoms themselves
Definition= amount of force per unit area
Units: Torr, atm, mmHg, kPa, Pa, etc.
Standard Pressure =
Use Dimensional Analysis to convert from one unit to another!
c. Pressure
d. Gas Laws1. Boyle’s Law
Boyle’s Law = changes in pressure cause changes in volumeIndirect relationshipUses 2 sets of conditions for P and V, at a constant temperature
Boyle’s Law Equation and Calculations
Boyle’s Law Equation:P1V1 = P2V2
At constant Temperature!A(n) ____________ Relationship between pressure and volume
Ex.] If the initial pressure inside a balloon is 0.95atm with a volume of 0.25L, what will the volume be when the pressure is decreased to 0.75atm and the temperature remains constant?
Boyle’s Law Examples cont.’
Ex.] The volume of gas inside a tank is 53.2L at a pressure of 0.55atm. What will the new pressure be when the volume is decreased to 35.7L at constant temperature?
2. Charles’ Law
Charles’ Law is a temperature and volume relationshipChanges in temperature cause changes in volume, at constant pressureTemp line crosses volume axis at –273 degrees celsius
Charles’ Law Equation and Calculations
Charles’ Law Equation
V1 = V2
T1 T2
At constant Pressure!A(n) ______________
relationship!
Special Note:Special Note:
ALL temperatures HAVE to be converted into KELVIN!!!
Temp oC + 273 = Temp K
Charles’ Law Examples cont.’
Ex.] The temperature of 0.33L of gas inside a balloon is C. What will the volume be when the temperature changes to 1.0oC at constant pressure?
Ex.] A 2.25L sample of air has a temperature of 25C. What will the temperature be when if volume changes to 1.13L at constant pressure?
3. Gay-Lussac’s Law
This is a pressure and temperature relationship, at constant volume.It is a ___________ relationship!
Temperatures need to be in KELVIN!!
Gay-Lussac’s Equation and Calculations
Equation:
P1 = P2
T1 T2
Occurs at constant volume!!
Ex.] The pressure inside a container is 0.98atm at 100C. What is the new temperature when the pressure increases to 2.25atm?
4. Combined Gas Law
Pressure, temperature, and volume condition changes can be related for two sets of conditions with the Combined Gas Law
P1V1 = P2V2
T1 T2
Combined Gas Law Example
Ex.] A 75mL sample of gas is at STP. What will the volume become if the temperature is raised to 75oC and the pressure is increased to 945 torr?
5. Avogadro’s Law
Established by the work of Avogadro What value did he generate from his work
with gases?
A moles vs. volume relationship at constant temperature and pressure
V1 = V2
n1 n2
6. Ideal Gas Law
The “Ideal Gas Law” defines the variables of a gas during one set of conditionsUses gas law constant, R, for calculations
R = 0.0821 L*atm/mol*K
PV = nRT
NOTES: Pay attention to
units Use units of gas
constant and convert accordingly
SINGLE SET OF CONDITIONS!!!
Ideal Gas Law Example
Ex.] Calculate the volume of 0.049mol of a gas whose pressure is 1.95atm at 3oC.
Ex.] Calculate the volume of 0.75mol of methane at 303K and a pressure of 0.758atm.
C. Van der Waals Equation
This is an alteration of the Ideal Gas Equation that accounts for the differences between ideal and real gases
Adds constants for specific substances to adjust volumes and attractive forces
F. Phase Diagrams
Phase Diagrams are temperature vs. pressure graphs for a substanceDiagrams allotropes and shows special temperatures: Critical Point Triple Point Supercritical Fluids
Phase Diagram of Carbon
Phase Diagram for Carbon Dioxide
Phase Diagram of Water
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