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