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