Agenda:
Thermochemistry Heating & Cooling Curves – a review Graphing temperature change Phase Change Diagrams Why are some compounds liquids
and gases at room temperatures ?
Homework:
Characteristics of Solids, Liquids & Gases Sort the terms into 3 columns: S, L, G
(Hint: Look for 3 cards with similar wording and determine which best fits solid, liquid or gas)
Solid Liquid Gas
Most substances, like water, can exist in all three states.
A cloud is made of water vapor, a type of gas.
An iceberg is made of water in solid form.
This glass contains liquid water.
WHAT ARE THE CHANGES OF STATE?
GAS
SOLID LIQUID
Deposition
Sublimation
Boiling / EvaporationCondensation
Freezing
Melting
Which are endothermic?
Which are exothermic?
Changing States (Phase changes)
SolidGas
Liquid
Increase Thermal Energy (Heat up)
Decrease Thermal Energy (Cool off)
Where on the picture would we place: - Melting Point?- Boiling Point? - Condensing Point?- Freezing Point?
States of matter, energy & phase changesEnergy levelEnergy changePhase changesMP/BP
Entropy= degree of disorder
Melting point Melting - change from solid to liquid Melting point - SPECIFIC temperature when
melting occurs. Each pure substance has a SPECIFIC melting
point.Examples:M.P. of Water = 0°C (32°F) M.P. of Nitrogen = -209.9 °C (-345.81998 °F)M.P. of Silver = 961.93 °C (1763.474 °F) M.P. of Carbon = 3500.0 °C (6332.0 °F)
Melting Point Particles of a solid vibrate so fast that they
break free from their fixed positions.
Solid Liquid
Increasing Thermal Energy
Melting point
Vaporization Vaporization – change from liquid to gas Vaporization happens when particles in a
liquid gain enough energy to form a gas.
GasLiquid
Increasing Thermal Energy
Boiling point
Two Kinds of Vaporization Evaporation – vaporization that takes
place only on the surface of the liquid Boiling – when a liquid changes to a gas
BELOW its surface as well as above.
Boiling Point Boiling Point – temperature at which a
liquid boils Each pure substance has a SPECIFIC
boiling point.Examples:B.P. of Water = 100°C (212°F) B.P. of Nitrogen = -195.79 °C (-320.42 °F)B.P. of Silver = 2162 °C (3924 °F) B.P. of Carbon = 4027 °C (7281 °F)
States of matter, energy & phase changesEnergy levelEnergy changePhase changesMP/BP
Entropy= degree of disorder
Heating and Cooling Curves of a Substance Representing MP, BP, CP, FP
Heating Cooling
Energy (heat) added Energy (heat) released:
Energy requirements for water Three formulas : specific heat Q = mCp∆T
heat of fusion Q= mHf
heat of vaporization Q= mHv
Heating Cooling
Energy (heat) added Energy (heat) released:
Energy calculations related heating or cooling specific substances Specific heat (Cp)
Latent heat Heat of fusion (Hf) Heat of vaporization (Hv)
Use reference tables – values for each pure substance
Heat calculations – 3 formulas
Specific heat = heat required to raise the temperature of 1 gram of substance 1 °C
Formula: Q = mCp∆T Specific heat
Specific for each pure substance Use reference tables
Heat calculations – 3 formulas
Heat of fusion - Amount of heat added to melt a substanceAmount of heat released to freeze a
substance
Formula Q= mHfSpecific for each pure substance Use reference tables
Heat calculations – 3 formulas
Heat of vaporization- Amount of heat added to boil a substanceAmount of heat released to condense a
substance
Formula Q= mHvSpecific for each pure substance Use reference tables
Heat energy In a heat calculation
problem, if the problem asks about melting/freezing you would multiply the mass times _____________________. heat of fusion heat of vaporization or specific heat
In a heat calculation problem, if the problem asks about vaporizing/condensing of steam, you would multiply the mass times ________. Heat of fusion Heat of vaporization Specific heat
In a heat calculation problem, if the problem asks about a change in temperature, you would multiply the mass times ___________________ times the change in temperature. Heat of fusion Heat of vaporization Specific heat
Thermochemistry Problems related to water
1. How much heat is required to raise the temperature of 789 g of water from 25oC to 70oC?
2. How much heat is released when 432 g of water cools from 71oC to 18oC?
3. How many joules of heat are given off when 5.9 g of
steam cools from 175oC to 125oC?
4. How many joules does it take to melt 35 g of ice at 0oC?
5. How much heat is released when 85 g of steam condense to liquid water?
6. How much heat is necessary to raise the temperature
of 25 g of water from 10 oC to 60 oC?
7. How much heat is given off when 50 g of water at 0oC
freezes?
How much energy is needed to heat water from a solid to a vapor?
Graph the data – using most of the graph paper
Time (when heat energy is added) Resulting temperature
See Textbook
Review: Heating curve with heat formulas
Scroll down http://www.kentchemistry.com/links/Matter/
HeatingCurve.htm
What factors impact change?
Intermolecular forces Energy Conditions: T, P, V, amount,
Phase Diagrams: What is added to this diagram? Why?
Phase diagrams
http://www.youtube.com/watch?v=fLOPaJ8lcr8&feature=endscreen&NR=1
T °C 200 °C -2°C 100 °C -2 °C 30°C 100 °CP - atm 1 atm 1 atm 100 atm 0.001 atm 0.8 atm 1 atm
Phase Liquid Vapor
For Water
A = B= C= D=
PHET States of Matter http://phet.colorado.edu/en/simulation/stat
es-of-matter
Phase Diagrams. Use the phase diagram for water below to answer the following questions.
What is the state of water at 2 atm and 50 C?
What phase change will occur if the temperature is lowered from 80C to -5C at 1 atm?
You have ice at -10C and 1 atm. What could you do in order cause the ice to sublime?
Review: Interpreting Phase Diagrams
Interpreting a Phase Diagramof Water at varying pressuresExample: 100 atm
1) What is the normal melting point of this substance? ________ 3) What is the normal boiling point of this substance? ________ 4) What is the normal freezing point of this substance? ________ 5) If I had a quantity of this substance at a pressure of 1.25 atm and a temperature of 00 C and heated it until the temperature was 7500 C, what phase transition(s) would occur? At what pressure(s) would they occur? 6) At what temperature do the gas and liquid phases become indistinguishable from each other? ________
7) If I had a quantity of this substance at a pressure of 0.25 atm and a temperature of -1000 C, what phase change(s) would occur if I increased the pressure to 1.00 atm? At what temperature(s) would they occur?
Water: Connecting Phase Diagram and Heating Curve
Vapor Pressure – Physical Equilibrium
The vapor pressure is the pressure measured when there is an equilibrium between the gas and liquid phases. The rates of condensation and vaporization
are equal.
Vapor pressure
http://www.chem.purdue.edu/gchelp/liquids/vpress.html
Discovery Ed video
Resources for S, L, G
http://www.kentchemistry.com/links/Matter/HeatingCurve.htm
How does the chemical composition of a substance impact whether it is a gas, liquid or solid at room temperature?
Factors that Impact State of Matter1. Type of compound – Ionic, Covalent,
Metallic2. Shape3. Size4. Polarity
Together impacts intermolecular forces
Shapes of Molecules
https://ed.ted.com/lessons/what-is-the-shape-of-a-molecule-george-zaidan-and-charles-morton
PHET simulation (?) http://phet.colorado.edu/en/simulation/mol
ecule-shapes
Intermolecular Forces
Impact state of matter for moleculesCovalent Compounds
Forces between moleculesNot between individual atoms
Much weaker than the bonds within a molecule (intramolecular bond)
Much weaker than ionic, covalent & metallic bonds
Intermolecular Forces
Three Types Hydrogen Dipole – dipoleLondon Dispersion (Van der Waals)
Based on weak attraction between molecules partial negative – partial positive
Polarity http://
phet.colorado.edu/en/simulation/molecule-polarity
Use real molecules tabMolecular dipolesElectronegativity Electron density or electrostatic potential
Note: VSEPR – valence shell electron pair repulsion impacts shape
Types of Intermolecular Forces
Strongest intermolecular forceHydrogen “bond” (~ 10% of a covalent bond)Molecule must be polar (+ and – sides)H in one molecule is attracted to the N,O,F of
another molecule
Hydrogen Bond - bad choice of words – an attractive force , not a bond
Hydrogen “bonds”: attraction between H with N, O, F
Types of Intermolecular Forces
Other intermolecular forces Dipole-dipole – all polar molecules (weaker)
London dispersion forces – all molecules (weakest)
Dipole-dipole
Based on polarity of molecules
Found with polar covalent compounds
Use with elements other than H attracted to N, O or F
London Dispersion Weakest Temporary polarity
Based on movement of the electrons around the nucleus
Impacts all molecules – non-polar and polar
Why is water unique? Why does ice float on water? https://
ed.ted.com/lessons/why-does-ice-float-in-water-george-zaidan-and-charles-morton
Hydrogen bonds -