Chemical Equilibrium

1. Chemical Equilibrium

2. Reversible Reactions • liquid + heat → vapor • vapor + cooling → liquid Products formed react to produce starting reactants A + B → C + D Forward (right) C + D → A + B Reverse (left) Simultaneous

3. Reaction Rates • Speed w/ which reaction proceeds • Varies • Temperature • Concentration • Catalysts • Chemical kinetics

4. What’s going on?

5. Dynamic Equilibrium • Chemical equilibrium • Two or more systems • Oppose each other • (forward and reverse reaction) • Same time • Same rate When rate of forward reaction = rate of reverse reaction…Dynamic Equilibrium is attained!

6. Equilibrium

7. Le Chatelier • If stress is applied to a system in equilibrium, the system will respond in such a way as to relieve that stress and restore equilibrium under a new set of conditions.

8. Le what??? • If change is imposed on a system in equilibrium… • then the system will adjust to a new equilibrium…

9. How does this work? • What will effect a chemical reaction? • Pressure • Concentration • Temperature • Volume • Catalyst

10. Concentration and Equilibrium • Concentration effects equilibrium • Effect on reactants is determined by experiment • What happens if you increase the reactants of the following reaction? • H2(g) + I2(g) 2HI(g) • Increases the number of reactants available for collisions… • What happens to the rate of the reaction? • It increases • The system will establish a new equilibrium

11. H2(g) + I2(g) 2HI(g) • What happens if we increase the concentration of [H2]? • Rate to the right increases • Reactants are used faster than products are produced • HI is produced faster than it is used • Eventually, equilibrium is reached • [I2]decreases and [HI] increases

12. Equilibrium and Volume • If one or more of reactants are a gas and the reaction is closed, then you will see significant changes to equilibrium with change to volume • How? • If you decrease the volume of the gas, what effect does that have on the reaction? • Think about the Ideal Gas Law…what would it do the concentration of the gas? • Increase!

13. CaCO3(s)825°C CaO(s) + CO2(g) • Decrease the volume • The reverse reaction speeds up • Equilibrium shifts to the left • WHY? • Decreasing the volume of the container increases the concentration of the carbon dioxide • WHY? • It’s the only gas! • What happens to pressure if you decrease volume? Think… • Pressure will increase. (Boyle’s Law and Ideal Gas Law)

14. If volume decreases, pressure increases • If a system is all gas; shift in reaction and equilibrium will be toward the side of the reaction that contains the least molecules • Why? • By shifting this way the system is trying to reduce the number of molecules and thus lower the pressure

15. Haber Process

16. Temperature and Equilibrium • Increase temperature; increase rate • Why? • KE increases (what is KE) • Forward and reverse increase • How will equilibrium shift? • Toward the side of the equation that absorbs the heat • Why? • Greater increase occurs • Exothermic reactions favor a left shift • Endothermic reactions favor a right shift

17. Catalyst on Equilibrium • Catalyst • Influence rate / affects speed • Not consumed during reaction • Lowers activation energy • DOES NOT SHIFT EQUILIBRIUM

18. Activation Energy • Minimum energy needed for reaction to occur • No change to • Energy • Reactants • Products

21. Equilibrium Constants • Reversible reactions • Concentration of products and reactants is constant • @ equilibrium, rate of forward reaction = rate of reverse reaction • Why is this significant? • Equilibrium constant

22. Keq • @ particular temperature • For the general equation aA + bB ⇄ cC + dD

23. Significant of Keq • Magnitude indicates extent the forward or reverse reaction takes place • If Keq > 1, the amount of product at equilibrium is greater than the amount of reactants • If Keq < 1, amount of reactants at equilibrium is greater than the amount of products • If Keq is large, the reaction will go forward to completion • If Keq is small, the reaction will go to the left