Rates of Reaction and Equilibrium

1. Rates of Reaction and Equilibrium • Rates of reaction = kinetics • Equilibrium = balance

2. To react, atoms must get together: • Called the collision theory: • Students act a chemical reaction • 1. • 2. • 3.

3. To react, atoms must: 1. Get together (collide) 2. Get together in the right way (orientation) Collide with the “correct” side of a molecule NO₂ + CO ↦ NO + CO₂ Carbon must hit the O side of NO₂ to get one of the O from the NO. 3. Get together with enough energy (force) so that the electrons can be shared/transferred • Activation energy (low or high)

4. Rate of chemical reaction: Reaction rate of a chemical reaction: measured by change in concentration per unit time

5. REACTION RATES: KINETICS • Rate that reactants turn into products • Measured by change in concentration (of reactants or products) 5 FACTORS AFFECTING REACTION RATES 3 factors relate to energy 2 factors relate to the particles

6. Review collision theory • Chemical reactions happen when atoms and compounds collide with each other • Collide with sufficient force to break bonds • Collide in the right position (orientation)

7. Factors affecting collision theory - Why? Energy Characteristics Concentration Surface area • Temperature • Agitation • Catalysts

8. Energy & kinetics (rate) • 1. temperature: increases temp INCREASES reaction rates Why? *particles move faster and collide with greater intensity 2. agitation: increases reaction rate Why? *increases likelihood of particles being exposed to one another; increase in collisions examples: shaking, stirring

9. Energy & kinetics 3. catalysts: substance that increases the reaction rate without being used up in the reaction. Why? * lowers the ACTIVATION energy; sort of “invites” reacting particles together so they will react

10. Solutions & kinetic • concentration: increasing concentration of reactants increases rate Why? *increasing # particles increases chance of collision resulting in a reaction

11. 2. surface area: increasing will cause reaction rate to increase Why? *greater exposure of reacting particles to each other examples: pulverizing, crushing, chopping up, etc Example: Logs vs. twigs

12. Collision Theory • Speed up the rate of reaction • https://www.youtube.com/watch?v=OttRV5ykP7A

13. Chemical Equilibrium = Balance

14. Chemical EquilibriumKey Terms • Reversible reactions • Balance • Impacted by concentration, temperature and pressure • Closed system (no new reactants added, no product is removed) • Equilibrium constant • Keq = [products] [reactants]

15. Chemical Reaction Equilibrium • Reversible reactions: ↔⇄ • Explain what a reversible reaction will do to products and reactants

16. Chemical Reaction Equilibrium • Reversible reactions: ↔⇄ • Often happens naturally • Products can be turned back to reactants • In other words: Products recombine to form the original substances .

17. Reversible reactions and Equilibrium • Equilibrium = balance between the amount of reactants and products in a reversible reaction Needs a closed system: no additional reactants added and no products are taken away or escape as a gas) Dynamic equilibrium Forward and backward reactions taking place at the same rate

18. Chemical Equilibrium

19. Chemical Equilibrium = Balance

20. Achieving equilibrium: After a period of time, the concentrations of reactants and products will stabilize

21. Le Chatelier Principle • If you change the conditions, the position of the equilibrium will shift to oppose the change. • Apply stress

22. Upsetting the equilibrium to make more product Upsetting the equilibrium = shifting the equilibrium • Change temperature If an endothermic reaction -absorb or release heat? -example of types of reaction? CaCO₃ + heat ⇄ CaO + CO₂ Add more heat (raise the temperature) to make more product If an exothermic reaction– reduce the amount heat (lower the temperature) to make more product Reaction will try to replace the heat that was taken away

23. Upsetting the equilibrium to make more product • Change the pressure • Important when gases react • Many reactions will have greater volume on one side (more product or more reactant) If we increase the pressure – The reaction will “favor” the reaction side with less volume If we lower the pressure – The reaction will “favor” the reaction side with more volume N₂ + 3 H₂ ⇄ 2NH₃

24. Haber Process • TED Ed Lessons • https://ed.ted.com/lessons/the-chemical-reaction-that-feeds-the-world-daniel-d-dulek • New concept: equilibrium

25. Le Chatelier Principle • If you change the conditions, the position of the equilibrium will shift to oppose the change.

26. Stresses disrupt the balance

27. Equilibrium constant • aA + bB⇆ cC + dD • Keq= [C] [D] [A] [B] • Example: N₂ + 3 H₂ ⇄ 2NH₃ • Keq = [NH₃]² [N₂] [H₂]³ Add coefficients at exponents Will use equilibrium constant when determining pH and pOH

28. Issues- Chemical reactions Good & Evil • Haber received much criticism for his involvement in the development of chemical weapons in pre-World War II Germany, both from contemporaries and from modern-day scientists. • The research results show the ambivalence of his scientific activity: on the one hand, development of ammonia synthesis for the manufacture of explosives and of a technical process for the industrial manufacture and use of poison gas in warfare; but on the other hand, development of an industrial process without which the food supply for today's world population would be greatly diminished

29. Review: Energy in chemical reactions Exothermic chemical reaction

30. Review: Energy in chemical reactions Endothermic chemical reaction