Bell Ringer

Chemical Equilibrium A reversible reaction is one in which the reactants are changing into products and products are changing into reactants at the same time

Reversible Reactions Here is an example of a reversible reaction. 2SO2(g) + O2(g)  2SO3(g) 2SO2(g) + O2(g)  2SO3(g) The first reaction is called the forward reaction. The second reaction is called the reverse reaction. 2SO2(g) + O2(g) 2SO3(g) The double arrow tells you that the reaction is reversible.

Establishing Equilibrium When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium.

Example Conditions at Equilibrium Chemical equilibrium is a dynamic state.

Le Châtelier’s principle If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress. Three stresses that effect equilibrium are: Concentration Temperature Pressure

1. Concentration Changing the amount, or concentration, of any reactant or product in a system at equilibrium disturbs the equilibrium.

2. Temperature Increasing the temperature causes the equilibrium position of a reaction to shift in the direction that absorbs heat.

3. Pressure Equilibrium systems in which some reactants and products are gases can be affected by a change in pressure. The system will shift toward the least number of moles of gas

Pressure When the plunger is pushed down, the volume decreases and the pressure increases. Initial equilibrium Equilibrium is disturbed by an increase in pressure. A new equilibrium position is established with fewer molecules.

PCl5(g) + heat PCl3(g) + Cl2(g) Applying Le Châtelier’s Principle What effect will each of the following changes have on the equilibrium position for this reversible reaction? PCl5(g) + heat PCl3(g) + Cl2(g) a. Cl2 is added. b. Pressure is increased. c. Heat is removed. d. PCl3 is removed as it forms.

CH4(g) + 2H2S(g) ↔ CS2(g) + 4H2(g) For the reaction below, which change would cause the equilibrium to shift to the right? CH4(g) + 2H2S(g) ↔ CS2(g) + 4H2(g) (a) Decrease the concentration of dihydrogen sulfide. (b) Increase the pressure on the system. (c) Increase the temperature of the system. (d) Increase the concentration of carbon disulfide. (e) Decrease the concentration of methane.

What would happen to the position of the equilibrium when the following changes are made to the equilibrium system below? 2SO3(g) ↔ 2SO2(g) + O2(g) (a) Sulfur dioxide is added to the system. (b) Sulfur trioxide is removed from the system. (c) Oxygen is added to the system.

Predict the effect of decreasing the temperature on the position of the following equilibria. H2(g) + Cl2(g) ↔ 2HCl(g) + 49.7 kJ (b) 2NH3(g) ↔ N2(g) + 3H2(g) Δ H = 37.2 kJ (c) CO(g) + H2O(g) ↔ CO2(g) + H2(g) Δ H = -27.6 kJ

What would happen to the position of the equilibrium when the following changes are made to the reaction below? 2HgO(s) ↔ Hg(l) + O2(g) (a) HgO is added to the system. (b) The pressure on the system increases.

Classwork: New Book Full sentences P.615 17 and 18, These are not m/c P. 640 #97 (NOT MULTIPLE CHOICE!)

For the reaction below, predict the equilibrium shift when each of the following changes occurs. This is an endothermic reaction. CH4(g) + 2H2S(g) ↔ CS2(g) + 4H2(g) (a) Decrease the concentration of dihydrogen sulfide. (b) Increase the pressure on the system. (c) Increase the temperature of the system. (d) Increase the concentration of carbon disulfide. (e) Decrease the concentration of methane.

Exit Ticket The Haber Process for the manufacture of ammonia from nitrogen and hydrogen involves this reversible reaction: N2 + H2 yields NH3 + heat The ΔH value shows that the reaction is exothermic. a) What would be the effect on the position of equilibrium if you increased the pressure? Explain your answer using Le Chatelier's Principle. b) In order to get the maximum possible percentage of ammonia in the equilibrium mixture, would you choose to use a high or a low temperature? Explain your answer using Le Chatelier's Principle. c) If you were a manufacturer, would there be any disadvantages in using the temperature you chose in part (b)?