Download Unit 4: Themodynamics

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
= 4.184 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 H20 when some
process occurs in it
 Q = “heat change” due
to ΔT
 Turn in Endo v. Exo Labs
 8th 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 = 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.
 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
 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
95,000 cal
1.
1.
400,000 J
19.9 cal
3. 2,400 cal
2.
1.
10,000 J
25,000 cal
4.
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.
2.
3.
4.
5.
What was the purpose of this lab?
What did you learn in this lab?
How does the data you collected provide evidence for
what you learned?
What are possible sources of error in the lab?
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 = Hproducts – Hreactants
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 < Ti
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 > Ti
 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 = 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 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!
ΔH
ΔS
Spontaneity
Exothermic
+ Value
(disordering)
- Value
(ordering)
+ Value
(disordering)
- Value
(ordering)
Always
spontaneous
Spontaneous at
lower T
Spontaneous at
higher T
Never
Spontaneous
Exothermic
Endothermic
Endothermic