I. Phases Defined and Characterized 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 rates Somewhat strong IMF’s Volume fixed shape depends on container

d. Gas High KE Low attractive forces between molecules No definite shape or volume; depends upon container Particles spaced far, far apart

Phases Summary Chart Solids Liquids Gases Energy Entropy [disorder] Shape, Properties

“Heating and Cooling Curves” 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 Evaporation or Vaporization Condensation Fusion Solidification 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 TEMPERATURE Sections with only 1 phase have KE changes Ex.] Changes in PE occur during a phase change when the temperature is CONSTANT Phase changes occur on flat sections Ex.]

Heat of Fusion Equation… Heat of Fusion The 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 Equation… Heat of Vaporization the 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 INDIRECTLY 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 Deposition

III. Temperature Average KE of particles within an area Measured 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 Pressure Units 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 do Based on ideal gas equation: PV=nRT Describes 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 Have no attractive forces between particles Particles have no relevant volume Have attractive forces between their particles Particles themselves have a definite volume

The MOST Ideal of the Real Gases are... Most IDEAL Gases Most IDEAL Conditions Hydrogen Helium Why?... Both have very small volumes Both have very weak attractive forces HIGH Temperature Low 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

c. Pressure 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!

d. Gas Laws 1. Boyle’s Law Boyle’s Law = changes in pressure cause changes in volume Indirect relationship Uses 2 sets of conditions for P and V, at a constant temperature

Boyle’s Law Equation and Calculations 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 relationship Changes in temperature cause changes in volume, at constant pressure Temp line crosses volume axis at –273 degrees celsius

Charles’ Law Equation and Calculations Special Note: ALL temperatures HAVE to be converted into KELVIN!!! Temp oC + 273 = Temp K Charles’ Law Equation V1 = V2 T1 T2 At constant Pressure! A(n) ______________ relationship!

Charles’ Law Examples cont.’ Ex.] The temperature of 0.33L of gas inside a balloon is 21oC. 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 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 conditions Uses 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 substance Diagrams allotropes and shows special temperatures: Critical Point Triple Point Supercritical Fluids

Phase Diagram of Carbon

Phase Diagram for Carbon Dioxide

Phase Diagram of Water