1. Thermochem

2. Objectives
Today I will be able to:
Diagram the heat transfer between the systems and surroundings for reactions
Calculate the energy absorbed or released during heat transfer
Informal assessment – monitoring student interactions and questions as we complete the notes and the polls
Formal assessment – analyzing student responses to the polls and practice problems

3. Lesson Sequence Evaluate: Warm Up Explain: Thermochemistry Notes
Evaluate: Closure

4. Warm Up
What is the difference between potential energy and kinetic energy?
What is the difference between temperature and heat?
What is the difference between endothermic and exothermic reactions?
Note: It is incorrect to say that an object contains a certain amount of heat… “heat exchange or transfer” is correct terminology

5. Objectives Today I will be able to:
Diagram the heat transfer between the systems and surroundings for reactions
Calculate the energy absorbed or released during heat transfer

6. Homework Organic Functional Groups Quiz
Friday, September 26
Bring your textbook to exchange!

7. Agenda
Warm – Up
Thermochemistry Notes
Closure

8. Thermochemistry
(Chapter 5)

9. First Law of Thermodynamics
Energy cannot be created or destroyed
Energy is conserved

10. System vs. Surroundings
System – all of the substances undergoing a physical or chemical change
Surroundings everything that is not apart of the system
Open, closed, isolated

11. A Piston is an Example of a Closed System

13. Heat transfer occurs until a thermal equilibrium is reached
smithplanet.com

14. Internal Energy (E)
Sum of all the kinetic and potential energies of the components of the system
our focus is typically the change in energy (ΔE)
ΔE = Efinal - Einitial

15. An increase of internal energy typically occurs when
Temperature increases
A phase change occurs
A chemical reaction initiates

17. Energy Diagram

18. Energy diagram of water
wps.prenhall.com

19. Determine the direction of energy transfer in the diagram

21. The internal energy of Mg(s) and Cl2(g) is greater than that of MgCl2(s). Sketch an energy diagram that represents the reaction MgCl2(s)  Mg(s) + Cl2(g)

22. Energy in a system comes from two places:
HEAT
WORK
Energy used to cause the temperature of an object to increase
Energy used to cause an object to move
NOTES: THE FIRST LAW ENDS

23. ΔE = q + w

24. Practice Problem 1
Gases A(g) and B(g) are confined in a cylinder-and-piston arrangement and react to form a solid product C(s): A(g) + B(g)  C(s). As the reaction occurs the system loses 1150 J of heat to the surroundings. The piston moves downward as the gases react to form a solid. As the volume of the gas decreases under constant pressure of the atmosphere, the surroundings do 480 J of work on the system. What is the change in internal energy of the system?

25. Answer ΔE = q + w q = -1150 J w= + 480J
ΔE = q + w = (-1150 J)+(480 J) = -670 J
Tells us the net value of energy transferred from the system to the surroundings was 670 J.

26. Practice Problem 2: You try
Calculate the change in the internal energy for a process in which a system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings

28. Closure
Complete the practice problems 5.3, 5.4, 5.7,5.25 Reread section 5.3 and 5.4 about enthalpy