1. CHEM 121 Chapter 6

2. Energy Ability to do work Potential Energy: Kinetic Energy: Heat:
Law of conservation of energy:

3. Energy Units
Joule
Kilojoule
calorie
Calorie

4. Nutritional Calories
Cal/g
A label on a bag of chips says that it contains 16 g fat, 34 g carbs, 4 g protein, and has a total of 300 Calories.
Are the nutrition facts accurate?

5. Spontaneity Spontaneous process: Nonspontaneous process: Exergonic:
Endergonic:

6. Collision Theory Reactions occur when molecules: Energy Diagram
Activation Energy:

7. Enzyme Reactions

8. Energy Diagrams

9. Bond Energies E needed to break bonds E released to make bonds
Bond Dissociation Energy

10. Energy Change in Reactions
H + Cl
ΔH = -103 kcal/mol
2 NH3 (g)
ΔH = 22 kcal/mol
Products:
Reactant:

11. Reaction Rate
Speed of a reaction
Measured by the time needed:

12. What affects reaction rates?

13. Reversible Reactions Many reactions can go forward AND backwards
Chemical Equilibrium

14. Chemical Equilibrium

15. Equilibrium Constants
coefficients
reactants
products

16. Practice
Balance and write the equilibrium expression for each of the following:
The reversible reaction of phosphorous trichloride combining with chlorine to form phosphorous pentachloride.
(All are gases.)

17. Equilibrium
Homogeneous equilibrium:
Heterogeneous equilibrium:

18. Calculating Equilibrium Constants
N2O4 (g) NO2 (g) 2
Must be determined experimentally
At 100 °C, once this reaction reaches equilibrium, the concentration of N2O4 is 0.45 M and NO2 is 0.31 M.
What is the value of Kc?

19. Equilibrium Constants
Large Kc value:
Greater concentration of reactants or products?

20. Equilibrium Constants
Small Kc value:
Greater concentration of reactants or products?

21. Practice Will each of the following favor reactants or products?
Reaction with Kc = 2.9 x 10-12
Reaction with Kc = x 105

22. Calculating Concentrations at Equilibrium
Carbon monoxide and hydrogen gas react reversibly to form CH4 (g) and water vapor.
What is the concentration of CH4 at equilibrium?
At equilibrium at 1000 °C, the concentrations of hydrogen, carbon monoxide, and water are 0.30 M, 0.51 M, and 2.0 M, respectively. (Kc at 1000 °C = 260)

23. Le Châtelier’s Principle
At equilibrium, concentrations of substances do not change.
If a stress is put on the reaction at equilibrium, the equilibrium will _______________________
What changes count as stress?

24. Effect of Concentration Changes
NO2 (g) NO (g) + O2 (g)
What is the effect on the equilibrium?
Add NO2?
Add O2?
Remove NO2?
Remove NO?

25. Effect of Pressure Changes
If P increases, equilibrium shifts to side with ____________________________
If P decreases, equilibrium shifts to side with ____________________________
NO2 (g) NO (g) + O2 (g)

26. Effect of Temperature Changes
If T increases, equilibrium shifts to _____________
If T decreases, equilibrium shifts to _____________
Endothermic:
A (g) B (g) + C (g)
Increase the temperature?

27. Practice
Consider the exothermic reaction between nitrogen gas and hydrogen gas, creating ammonia gas (NH3).
Write a balanced equation for this reaction.
Which direction will the equilibrium shift if:
T is increased?
Ammonia is removed?
A catalyst is used?
Hydrogen is added?