Chemistry 312: Spring 2015

Review Endo v. Exo HW Endo v. Exo Pre Lab Questions Endo v. Exo Lab Notes on Specific Heat HW: Complete Lab Analysis Questions

What is thermodynamics, and how can it be measured?

Thermo = heat Dynamics = movement The study of heat moving into and out of things Present in everyday situations Roasting Marshmallows Fuel in cars Food 1 Calorie (food) kcal = 1000 calories = kJ

Temperature: 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

Calorimetry = the science of measuring heat Observe ΔT when things absorb or release heat In lab, use Q=mc ΔT to measure energy change in H 2 0 when some process occurs in it Q = “heat change” due to ΔT

Turn in Endo v. Exo Labs 8 th Hour: Turn in endo v. exo review Recap Endo v. Exo and Heat v. Temp Notes: Calorimetry and equation Practice HW: complete Thermal Energy WS

Define: System Surroundings Endothermic Exothermic What is the difference between: Heat and Temperature?

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 = 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.

A 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 J/C*g

A 250g sample of water is cooled from 50C to 25C. How much heat was lost to the surroundings?

525 mL of water is heated so that its temperature increases by 115C. How much heat must have been given to the sample?

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?

Warm-Up Review HW What is C? Lab HW: Complete Lab and Calculations w/ Conclusion

1. 95,000 cal ,000 J cal 3. 2,400 cal 1. 10,000 J 4. 25,000 cal 1. 10,500 J

Recap Calorimetry Lab Write conclusion and turn in lab Practice Calorimetry problems Notes: Heats of reaction HW: Complete 5-7 on Thermal Problems WS

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?**

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?

Review HW and HW Questions Team Calorimetry Activity Notes: Enthalpy Heat of Reactions Potential Energy Diagram Activity HW: Finish PE diagram

What is enthalpy and how can it be used to determine if a reaction is endo/exothermic

Where does the chemical energy come from (go to)? Chemical bonds breaking and forming H = enthalpy = heat content of a substance Comparing systems before and after change (enthalpy change) ΔH = H products – H reactants

Endothermic Endo = “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? Absorb Do surroundings gain or lose NRG? T f < T i

Exothermic Exo = “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? Release Do surroundings gain or lose E? How do you know? T f > T i

Ice melts when you touch it. Answer: Endothermic Ice cream melts Answer: Endothermic Propane is burning in a propane torch. Answer: Exothermic Water drops on your skin after swimming evaporate. Answer: Endothermic Two 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

What is enthalpy? How can enthalpy be used to determine endo/exo? What is activation energy?

What is Hess’ Law, and how can this be used to determine whether or not a reaction is exothermic or endothermic?

How 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 tables Formation of 1 mole of compounds from their elements

Using Hess’s Law to determine heats of reactions Start by writing and balancing desired equation Identify compounds in the equation and find ΔH for each chemical. Find a way to add up equations to match desired final equation If you reverse the rxn, sign of ΔH is changed If you multiply the rxn by a number, multiply ΔH Heat of formation of element in standard state = 0

Review Thermo Quiz Notes: Entropy and Gibbs Free Energy Spontaneous Reactions Review for Test: Concept Map Go over test format and finish review assignment HW: Complete the review assignment

What is entropy and how can free energy be used to determine if a reaction will occur spontaneously?

Entropy = S = measure of degree of order; randomness High entropy = greater disorder, more possibilities for arrangement Which state has greatest amount of entropy? ΔS = S products - S reactants

How are enthalpy and entropy used to predict reactions? Gibbs Free Energy = G = quantity of energy that is available or stored to cause a change Use the value of the change in G to predict if reaction is spontaneous ΔG = ΔH – (TΔS) ΔG = Negative = spontaneous ΔG = Positive Value = not spontaneous Note: T must be in Kelvin!

ΔHΔHΔSΔSSpontaneity Exothermic+ Value (disordering) Always spontaneous Exothermic- Value (ordering) Spontaneous at lower T Endothermic+ Value (disordering) Spontaneous at higher T Endothermic- Value (ordering) Never Spontaneous