1. Enthalpy (5.3)

2. Objectives – Today I will be able to: Define state function Calculate the enthalpy of a system Informal assessment – monitoring student interactions and questions as they complete the practice problems Formal assessment – analyzing student responses to the practice problems

3. Lesson Sequence Evaluate: Warm Up Explain: Enthalpy Elaborate: Enthalpy Calculations Evaluate: Closure

4. Warm Up Calculate the change in internal energy for a process in which a system absorbs 30 J of heat from the surroundings and does 44 J of work on the surroundings.

5. Answer E = q + w q = 30 J because heat was absorbed w = -44 J because work was done by the system E = 30 J + (-44 J) E = - 14 J

6. Objectives Today I will be able to: – Define state function – Calculate the enthalpy of a system

7. Homework Organic Functional Groups Quiz – Thursday, October 2 Bring textbook to exchange Finish practice problems

8. Agenda Warm Up Enthalpy Notes Practice Problems Exit Ticket

9. Enthalpy (5.3)

10. What two components make up the total energy of a system?

11. Work Mechanical work is the focus for chemical and physical changes Associated with a change in volume Constant pressure is maintained Zn(s) + 2H + (aq)  Zn 2+ (aq) + H 2 (g)

12. Work cont. Work involved in the expansion or compression of gases is called pressure – volume work w = - PΔV Units: L-atm Conversion factor 1 L-atm = 101.3 J

13. Practice Problem A fuel is burned in a cylinder equipped with a piston. The initial volume of the cylinder is 0.250 L, and the final volume is 0.980 L. If the piston expands against a constant pressure of 1.35 atm, how much work (in J) is done?

14. Answer w = -PΔV W = - (1.35 atm)(0.730 L) = -0.9855 L-atm -0.9855 L-atm (101.3J / 1 L-atm) = -99.8 J W = -99.8 J

15. Practice Problem 2

16. Answer

17. Enthalpy (H) Internal energy plus the product of the pressure and volume of a system H = E + PV The equation is used to account for the absorption/release of heat and work during a chemical or physical change Relates mainly to heat flow

18. Enthalpy is a state function State function – A property of a system that is determined by specifying the systems condition or state – Value of a state function depends only on the present state of the system, not on the path the system took to reach the state

19. Potential energy of hiker 1 and hiker 2 is the same eventhough they took different paths. 6.7 Example

20. Which of the following variables are examples of state functions? ΔE q w H PV

21. Enthalpy Change (ΔH) Change in heat exchange between a system and its surroundings at constant external pressure ΔH = ΔE + PΔV

22. Keep in mind… ΔH = ΔE + PΔV ΔH = (q p + w) – w ΔH = q p For most reactions the difference between ΔH and Δ E is small because there is not a lot of work If PΔV is small it can be ignored from calculations

23. Closure Complete practice problems: – 5.31, 5.32, 5.37,