agenda: thermochemistry heating & cooling curves – a review graphing temperature change phase...

Agenda:

Thermochemistry Heating & Cooling Curves – a review Graphing temperature change Phase Change Diagrams Why are some compounds liquids

and gases at room temperatures ?

Homework:

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:

Review: Heating curve with heat formulas

Scroll down http://www.kentchemistry.com/links/Matter/

HeatingCurve.htm

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= mHf

Specific 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= mHv

Specific 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

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

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?

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?

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

Elements that exist as gases at 250C and 1 atmosphere

Factors that Impact State of Matter1. Type of compound – Ionic, Covalent,

Metallic

2. Shape

3. Size

4. 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 -