1. First Law of Thermodynamics
Section 5.2
First Law of Thermodynamics

2. Objectives Explore the 1st law of thermodynamics
Explain why energy cannot be created or destroyed
Demonstrate how energy can be transformed and transferred

3. Key Terms Internal Energy 1st Law of Thermodynamics Endothermic
Exothermic
State function

4. First Law of Thermodynamics
Energy is neither created nor destroyed
Total energy of the universe is a constant; if system loses energy, it must be gained by the surroundings

5. Internal Energy, E
Sum of all kinetic and potential energies of all components of the system
Use Fig. 5.5

6. Internal Energy
Change in internal energy, E, is the final energy of the system minus the initial energy of the system:
E = Efinal − Einitial
Use Fig. 5.5

7. E in Chemical Reactions
Einitial  state of reactants
Efinal  state of products

8. E > 0 Efinal > Einitial
System absorbed energy from surroundings
Endergonic

9. E < 0 Efinal < Einitial
System released energy to the surroundings
Exergonic

10. Changes in E
When energy is exchanged between the system and the surroundings, it is exchanged as either heat (q) or work (w).
That is, E = q + w.

11. E, q, w, and Their Signs

12. Endothermic Process
Heat is absorbed by the system from the surroundings

13. Exothermic Process
When heat is released by the system to the surroundings

14. State Functions
Property of a system determined by specifying its conditions
Fixed conditions include temperature and pressure

15. E as a State Function No way to know precise internal energy
Depends only on initial and final states, not the change that occurred
Water can reach room temperature from either direction

16. Not State Functions q and w
E can stay the same, even when q and w are different

17. Ex: Discharging a battery
A: Coil wire shorts battery
No work done, energy lost as heat
B: Battery runs out after making a small motor turn in a fan
Battery does work and only some heat is released

18. A system that absorbs heat from the surroundings is an ________ process.
Endothermic
Exothermic

19. Correct Answer:
Endothermic
Exothermic

20. It is determined by many factors.
It is a numerical value.
It is calculated from multiple transactions.
It doesn’t depend on how money got into your account or was taken out; it only depends on the net total of all transactions.

21. It is determined by many factors.
It is a numerical value.
It is calculated from multiple transactions.
It doesn’t depend on how money got into your account or was taken out; it only depends on the net total of all transactions.