Chemistry 312: Spring 2015. Review Endo v. Exo HW Endo v. Exo Pre Lab Questions Endo v. Exo Lab...
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Transcript of Chemistry 312: Spring 2015. Review Endo v. Exo HW Endo v. Exo Pre Lab Questions Endo v. Exo Lab...
Chemistry 312: Spring 2015
Unit 4: Themodynamics
Review Endo v. Exo HW
Endo v. Exo Pre Lab Questions
Endo v. Exo Lab
Notes on Specific Heat
HW: Complete Lab Analysis Questions
Agenda 3/31
Essential question…What is thermodynamics, and how can it be measured?
What is thermodynamicsThermo = heatDynamics = movementThe study of heat
moving into and out of things
Present in everyday situationsRoasting MarshmallowsFuel in carsFood
1 Calorie (food) kcal = 1000 calories = 4.184 kJ
Temperature v. HeatTemperature:
measure of average kinetic energy of random motion of particles in a substance
Heat: measure of total amount of energy transferred from an object of a high temperature to an object of low temperature
How do we measure thermodynamicsCalorimetry = the
science of measuring heat
Observe ΔT when things absorb or release heatIn lab, use Q=mc
ΔT to measure energy change in H20 when some process occurs in it
Q = “heat change” due to ΔT
Turn in Endo v. Exo Labs8th Hour: Turn in endo v. exo review
Recap Endo v. Exo and Heat v. Temp
Notes: Calorimetry and equationPractice
HW: complete Thermal Energy WS
Agenda 4/1/2015
Define:SystemSurroundingsEndothermicExothermic
What is the difference between:Heat and Temperature?
Warm- Up
Q=mc ΔT Possible to measure Q for anything
All substances have a specific “c”c = specific heat
Heat energy needed to raise temperature of 1 gram of substance by 1ºC
Physical property of matter = each pure substance has a unique specific heat capacity
Water = 1 cal/g ºC = 4.180 J/g ºC
If Q is negative, what happened to E of stuff?
If Q is positive, what happened to E of stuff?
You will each need a partner, a white board and a marker.
White Boards!!
A 600.0 g sample of water is heated from 10. degrees Celsius to 100. degrees Celsius, what is the total heat gained by the water?
Specific heat of water is 4.184 J/C*g
Examples
A 250g sample of water is cooled from 50C to 25C. How much heat was lost to the surroundings?
Example 2
525 mL of water is heated so that its temperature increases by 115C. How much heat must have been given to the sample?
Example 3
A 15g sample of mercury is heated from 32C to 100C. If the specific heat of mercury is .0330 cal/g*C, how much heat must have been given to the mercury? Your answer should be in joules
How many calories are in a joule?
Example 4
Warm-Up
Review HW
What is C?Lab
HW: Complete Lab and Calculations w/ Conclusion
Agenda 4/2/2015
1. 95,000 cal1. 400,000 J
2. 19.9 cal3. 2,400 cal
1. 10,000 J
4. 25,000 cal1. 10,500 J
Answers to 1-3
Recap Calorimetry LabWrite conclusion and turn in lab
Practice Calorimetry problems
Notes: Heats of reaction
HW: Complete 5-7 on Thermal Problems WS
Agenda 4/6/15
Recall the procedure for the lab.
What was the purpose of the boiling water?How did you know the initial temperature of
the metal?
What was the purpose of the water in the Styrofoam cup?
How was the heat gained by the water related to the heat lost by the metal?**
Calorimetry Lab
Write a conclusion for this lab
1. What was the purpose of this lab?2. What did you learn in this lab?3. How does the data you collected provide
evidence for what you learned?4. What are possible sources of error in the
lab?5. What connections to the real world can be
drawn from this lab?
Conclusion
Review HW and HW Questions
Team Calorimetry Activity
Notes: EnthalpyHeat of Reactions
Potential Energy Diagram Activity
HW: Finish PE diagram
Agenda 4/7/15
EnthalpyWhat is enthalpy and how can it be used to determine if a reaction is endo/exothermic
Chemical Potential EnergyWhere does the chemical energy come from
(go to)?Chemical bonds breaking and forming
H = enthalpy = heat content of a substanceComparing systems before and after change
(enthalpy change)ΔH = Hproducts – Hreactants
EndothermicEndo = “within”ΔH of chemicals is
positive How does PE of
reactants compare to PE of products?
PE Products>PE Reactants
Do chemicals absorb or release E upon reaction?
AbsorbDo surroundings gain
or lose NRG?Tf < Ti
ExothermicExo = “outside of”ΔH of chemicals
negative How does PE of
reactants compare to PE of products?
PE Products<PE Reactants
Do chemicals absorb or release E upon reaction?
ReleaseDo surroundings gain or
lose E?How do you know?Tf > Ti
Ice melts when you touch it.Answer: EndothermicIce cream meltsAnswer: EndothermicPropane is burning in a propane torch.Answer: ExothermicWater drops on your skin after swimming
evaporate.Answer: EndothermicTwo chemicals mixing in a beaker give off
heat.Answer: Exothermic
Review Reaction/Energy Graph
Notes: Hess’ Law
Examples: Hess’ Law
HW: Complete Hess’ Law WS
Quiz Friday on Calorimetry and Hess’ Law
Agenda 4/8/15
What is enthalpy?
How can enthalpy be used to determine endo/exo?
What is activation energy?
Warm-Up
What is Hess’ Law, and how can this be used to determine whether or not a reaction is exothermic
or endothermic?
Hess’ Law
Hess’ LawHow can I determine the ΔH of a chemical?
How can you determine the ΔH of a full reaction?Hess’s Law
The overall heat of a reaction (ΔH ) is the sum of the ΔHs of each step in the process
Can obtain “heat of formation” (ΔH) data for compounds from tablesFormation of 1 mole of compounds from their elements
Using Hess’s Law to determine heats of reactionsStart by writing and balancing desired
equationIdentify compounds in the equation and find
ΔH for each chemical.Find a way to add up equations to match
desired final equationIf you reverse the rxn, sign of ΔH is changedIf you multiply the rxn by a number, multiply ΔH Heat of formation of element in standard state = 0
Directions for Hess’ Law
Review Thermo Quiz
Notes: Entropy and Gibbs Free EnergySpontaneous Reactions
Review for Test: Concept MapGo over test format and finish review
assignment
HW: Complete the review assignment
Agenda 4/14/15
EntropyWhat is entropy and how can free energy be used to
determine if a reaction will occur spontaneously?
Entropy = S = measure of degree of order; randomnessHigh entropy = greater disorder, more possibilities
for arrangementWhich state has greatest amount of entropy?ΔS = Sproducts - Sreactants
How are enthalpy and entropy used to predict reactions?Gibbs Free Energy = G = quantity of energy
that is available or stored to cause a changeUse the value of the change in G to predict if
reaction is spontaneousΔG = ΔH – (TΔS)ΔG = Negative = spontaneousΔG = Positive Value = not spontaneousNote: T must be in Kelvin!
ΔG = ΔH – (TΔS)Using Free Energy Equation
ΔH ΔS Spontaneity
Exothermic + Value(disordering)
Alwaysspontaneous
Exothermic - Value(ordering)
Spontaneous at lower T
Endothermic + Value(disordering)
Spontaneous at higher T
Endothermic - Value(ordering)
Never Spontaneous