Rates of Reaction & Equilibrium

1. Rates of Reaction & Equilibrium

2. Part 1:Rates of Reaction

3. Collision Theory • Atoms/molecules must collide in order to react. • Increasing the rate of collision will increase how fast a reaction takes place

4. Effective collisions depend upon: • Nature of Reactants • Concentration • Temperature • Surface Area • Catalysts

5. Activation Energy • The energy put in to a reaction to get it started. • Small activation energies can be as simple as heat from the classroom, or the spark from a striker. • Large activation energies can be a lot of heat (like baking a cake). • Creates an “activated complex”.

6. Activation Energy is B

7. Activated Complex

8. Catalysts • lower the activation energy, thus change the rate of rxn. • change the mechanism of a rxn, involving less activation energy • do not change the overall process • Do not get used up in the process. • Do not start a chemical rxn • ex. Enzymes

9. Catalysts lower activation energy

10. Inhibitor • a substance that interferes with the action of a catalyst. • reduces the amount of catalyst available and therefore lowers the reaction rate.

11. Enthalpy • Heat of reaction • The difference in potential energy (PE)between products and reactants represents Enthalpy • ΔH = Hproducts - Hreactants • table I

13. In an Exothermic reaction, energy is released, products have a lower P.E. than the reactants, and the sign of ΔH is negative. Exothermic graph. ΔH = C = amount of heat given off during rxn

14. In an Endothermic reaction, energy is absorbed, products have a higher P.E. than the reactants, and the sign of ΔH is positive. Endothermic graph. ΔH = (3) = amount of heat absorbed by rxn

15. Speeding up reactions: • Most reactions, especially Endothermic reactions, will go faster with higher temperatures • Exothermic reactions will be inhibited by high temperatures • Increasing surface area will increase rate of reaction • Increasing concentrations will increase rate of reaction

16. Reversible Reactions • A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. • Example: • Forward reaction: 2SO2(g) + O2(g) → 2SO3(g) • Reverse reaction: 2SO2(g) + O2(g) ← 2SO3(g)

17. Part 2:Equilibrium

18. Chemical Equilibrium • When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance • no net change occurs in the actual amounts of the components of the system. • (Concentrations of Products and Reactants do not change)

19. Types of equilibrium • Solution Equilibrium • dissolving is occurring at the same rate at precipitation • Phase Equilibrium • Vaporization occurring at the same rate as condensation • Reaction Equilibrium • Products are forming equal to the rate of the reverse reaction re-forming reactants

20. Equilibrium Graphs…

21. adding catalyst to a system that was already at equilibrium? • A catalyst will bring a system to equilibrium sooner • The rates of the forward and reverse reactions would increase but the overall net reactions would not change.

22. Le Châtelier’s Principle Concentration • If additional reactants (or products) are added to a reaction system at equilibrium, the eqpoint (point of equilibrium) will shift favoring the reaction that would relieve the stress.

23. Le Châtelier’s Principle Temperature • If additional heat were added to a reaction system at equilibrium (raise the temperature of the system), the eqpoint will shift favoring the endothermic reaction to relieve the stress. • An increase in temperature favors all reactions, but endothermic reactions benefit more.

24. Equilibrium Continued

25. Le Châtelier’s Principle Pressure • Changing the pressure of a system only affects reactions that have components in the gaseous phase. • If additional pressure were added to a system at equilibrium, the eqpoint will shift favoring the reaction that makes less gas molecules to relieve the stress.

26. The Haber Process • http://mail.kenton.k12.ny.us/~Bob_Ventola/chemistry/habermovie.swf

27. Law Of Chemical Equilibrium • ►When a reversible reaction reaches equilibrium at a given temp. the following mathematical relationship occurs • Ex. aA + bBcC + dD • ►lower case = coefficient • ►upper case = formula • § keq = [products] = [C]c[D]d [reactants] [A]a[B]b

28. Spontaneous Reactions • occur naturally and favors the formation of products at the specified conditions. • produce substantial amounts of products at equilibrium and release free energy. • fireworks

29. Entropy • is a measure of the disorder of a system. (randomness) (S) • §Recall that heat (Enthalpy) changes accompany most chemical and physical processes.

30. “E” words • Enthalpyis a measure of heat energy + value = endothermic - value = exothermic • Entropyis a measure of the disorder, randomness, or lack of organization of a system. • ex. solid (less random) - liquid - gas (more random) • High temp. = High entropy

31. Forces of the Universe • Systems move naturally toward • a decrease in Enthalpy ( - ΔH) • an increase in Entropy ( + ΔS) • The universe naturally makes things go to lower energy and more disorder.

32. Enthalpy, Entropy and Free Energy • every chemical reaction, heat is either released or absorbed and entropy either increases or decreases. • size and direction of enthalpy changes and entropy changes together determine whether a reaction is spontaneous

33. Gibb’s Free Energy Change • The difference between energy change (DH ) and entropy change (DS ) was studied by Willard Gibb • Gibb formula: ΔG = ΔH - TΔS • ΔG = Free energy change • ΔH= Total Heat • T = Temp in Kelvin • ΔS = Entropy

34. According to Gibb • ΔG = ΔH - TΔS • If ΔG= negative value, then reaction is spontaneous • If ΔG= positive value, then reaction is Non-spontaneous • Zero ΔGmeans reactions are at equilibrium.