agenda: thermochemistry heating & cooling curves – a review graphing temperature change phase...
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Agenda:
Thermochemistry Heating & Cooling Curves – a review Graphing temperature change Phase Change Diagrams Why are some compounds liquids
and gases at room temperatures ?
Homework:
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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:
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Review: Heating curve with heat formulas
Scroll down http://www.kentchemistry.com/links/Matter/
HeatingCurve.htm
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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
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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
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Heat calculations – 3 formulas
Heat of fusion - Amount of heat added to melt a substanceAmount of heat released to freeze a
substance
Formula Q= mHf
Specific for each pure substance Use reference tables
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Heat calculations – 3 formulas
Heat of vaporization- Amount of heat added to boil a substanceAmount of heat released to condense a
substance
Formula Q= mHv
Specific for each pure substance Use reference tables
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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
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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?
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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?
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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
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What factors impact change?
Intermolecular forces
Energy
Conditions: T, P, V, amount,
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Phase Diagrams: What is added to this diagram? Why?
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Phase diagrams
http://www.youtube.com/watch?v=fLOPaJ8lcr8&feature=endscreen&NR=1
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PHET States of Matter http://phet.colorado.edu/en/simulation/stat
es-of-matter
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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?
Interpreting Phase Diagrams
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Interpreting a Phase Diagramof Water at varying pressuresExample: 100 atm
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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?
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Water: Connecting Phase Diagram and Heating Curve
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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.
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Vapor pressure
http://www.chem.purdue.edu/gchelp/liquids/vpress.html
Discovery Ed video
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Resources for S, L, G
http://www.kentchemistry.com/links/Matter/HeatingCurve.htm
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How does the chemical composition of a substance impact whether it is a gas, liquid or solid at room temperature?
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Look at this list of gases. Make a conclusion related to the gases in terms of size and type of compound (bond type).
Room Temperature
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Elements that exist as gases at 250C and 1 atmosphere
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Factors that Impact State of Matter1. Type of compound – Ionic, Covalent,
Metallic
2. Shape
3. Size
4. Polarity
Together impacts intermolecular forces
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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
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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
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Intermolecular Forces
Three Types Hydrogen Dipole – dipoleLondon Dispersion (Van der Waals)
Based on weak attraction between molecules partial negative – partial positive
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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
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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
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Hydrogen “bonds”: attraction between H with N, O, F
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Types of Intermolecular Forces
Other intermolecular forces Dipole-dipole – all polar molecules (weaker)
London dispersion forces – all molecules (weakest)
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Dipole-dipole
Based on polarity of molecules
Found with polar covalent compounds
Use with elements other than H attracted to N, O or F
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London Dispersion
Weakest
Temporary polarity
Based on movement of the electrons around the nucleus
Impacts all molecules –
non-polar and polar
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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 -