1. Chapter 16 Equilibrium

2. How do chemical reactions occur? Collision Model Molecules react by colliding into one another. – This explains why reactions proceed faster at higher concentrations. Higher concentration of reactants leads to greater production of product. (More effective collisions) Effective collisions are collisions that break the bonds of reactants allowing products to form.

3. Also, more effective collisions occur at higher temperatures(higher kinetic energy). – More collisions Higher temperature = Higher kinetic energy (more collisions. Also, these collisions are more energetic. So, it is more likely that these higher energy collisions will break the bonds needed to reach the activated complex.

4. Activation Energy (Ea) The energy needed to break bonds

5. Enzymes and other catalysts lower Ea Catalyst- a substance that speeds up a reaction without being consumed. Enzymes- catalysts produced in our bodies.

6. Catalysts act by lowering Ea

7. Factors that Affect Reaction Rate 1.Concentration 2.Temperature 3.Presence of a Catalyst

8. The Equilibrium Condition Equilibrium usually implies balance or steadiness. BUT In chemistry there is another definition.

9. Equilibrium the exact balancing of two processes, one of which is the opposite of the other. Reversible reactions are often in equilibrium.

10. Reversible Reactions When writing reversible reactions use an arrow that points in both directions. N₂ + 3H₂ ↔ 2NH₃

11. As N₂ and H₂ are first combined the reaction for the formation of NH₃ can be observed. Until, finally the process appears to stop. What has happened? Actually, we have reached chemical equilibrium.

12. Chemical Equilibrium A dynamic state where the concentrations of all reactants and products remain constant. A + B ↔ C + D At chemical equilibrium the rate of the forward reaction equals the rate of the reverse reaction.

13. Le Chatelier’s Principle States that: When a change is imposed on a system at equilibrium, the position of the equilibrium shifts in a direction that tends to reduce the effect of that change.

14. Changing concentration of one of the reactants or products affects equilibrium. H₂O + CO ↔ H₂ + CO₂ If CO is added to the system, the [CO] will increase and additional product will be produced. This is often called a shift to the right. Right meaning products. If instead, additional H₂ is added the opposite will then occur. This will cause a shift to the left(reactants).

15. Changing volume of the container will also cause a shift. N₂ + 3H₂ ↔ 2NH₃ reactants = 4 mol gas products = 2 mol gas Since we know the volume of one mole of any gas at STP, (22.4L) as volume decreases the equilibrium will shift toward the lower number of moles of gas. In this case it shifts to the right, toward products. If volume was increased, instead, it would shift the opposite direction. To the left, toward reactants.

16. The effect of a change in temperature First write the equation including any energy needed or released. 2SO₂ + O₂ ↔ 2SO₃ + energy Energy released = exothermic If heat is added (temperature increase), the equilibrium should shift away from the product of energy. That would mean a shift to the left. A shift toward reactants.

17. Equation with energy as a reactant N₂ + O₂ + energy ↔ 2NO Energy needed = endothermic If heat is added (temperature increase), the equilibrium should shift away from the reactant of energy. That would mean a shift to the right. A shift toward products.