Regent ’ s Warm-Up Which is an empirical formula? (1) P 2 O 5 (3) C 2 H 4 (2) P 4 O 6 (4) C 3 H 6

Regent ’ s Warm-Up Which is an empirical formula? (1) P 2 O 5 (3) C 2 H 4 (2) P 4 O 6 (4) C 3 H 6

Reaction Equilibrium AIM: How does a reaction at equilibrium change when it is disturbed? DO NOW: What is equal at equilibrium?

Reaction Equilibrium We can change the concentrations of reactants and products by disturbing or “ stressing ” a reaction

Reaction Equilibrium When disturbed the reaction will make adjustments to restore equilibrium The new equilibrium position is different, which means the amounts of reactants and products are changed The change in equilibrium is called a “ shift ” in the equilibrium position

Henri Le Chatelier The chemist Henri Le Chatelier studied equilibrium conditions He developed rules for changing equilibrium based on his experiments

Le Chatelier ’ s Principle Any stress applied to a reaction in dynamic equilibrium causes the reaction to make a “ shift ” to relieve the stress A shift towards product formation is a shift to the right A shift towards reactant formation is a shift to the left Stresses to a reaction include: 1) Concentration changes 2) Pressure/volume changes 3) Temperature changes

Stress 1: Concentration Changes in the amount or concentration of a product OR reactant will disturb (stress) an reaction at equilibrium The reaction adjusts to minimize any stresses   in reactants causes a shift toward products   in products causes a shift toward reactants   in reactants causes a shift toward reactants   in products causes a shift toward products

Stress 1: Concentration Given the reaction (see image) at equilibrium: What occurs when the concentration of H 2 (g) is increased? 1. The rate of the forward reaction increases and the concentration of N 2 (g) decreases. 3. The rate of the forward reaction and the concentration of N 2 (g) both increase. 2. The rate of the forward reaction decreases and the concentration of N 2 (g) increases. 4. The rate of the forward reaction and the concentration of N 2 (g) both decrease Given the reaction (see image) at equilibrium: What occurs when the concentration of H 2 (g) is increased? 1. The rate of the forward reaction increases and the concentration of N 2 (g) decreases. 3. The rate of the forward reaction and the concentration of N 2 (g) both increase. 2. The rate of the forward reaction decreases and the concentration of N 2 (g) increases. 4. The rate of the forward reaction and the concentration of N 2 (g) both decrease

Stress 2: Pressure/Volume If the volume of a reaction changes the equilibrium is disturbed  in volume causes an  in pressure The equilibrium will shift to relieve pressure if the pressure is  and  pressure if the pressure is  Increasing and decreasing pressure is based on the # of moles of gas To  pressure there is a shift toward the side of the reaction with the least # of moles of gas Given the reaction (see image) at equilibrium: What occurs when the concentration of H 2 (g) is increased? 1. The rate of the forward reaction increases and the concentration of N 2 (g) decreases. 3. The rate of the forward reaction and the concentration of N 2 (g) both increase. 2. The rate of the forward reaction decreases and the concentration of N 2 (g) increases. 4. The rate of the forward reaction and the concentration of N 2 (g) both decrease

Stress 2: Pressure/Volume Ammonia is produced commercially by the Haber reaction:... (see image) The formation of ammonia is favored by 1. an increase in pressure 3. removal of N 2 (g) 2. a decrease in pressure 4. removal of H 2 (g)

Stress 3: Temperature Changing temperature alters both the equilibrium position and the equilibrium constant Reactions are either endothermic or exothermic If a fwd rxn is exothermic the rev rxn will be endothermic An  in temp causes a shift in the direction where heat is absorbed (endothermic)  in temp causes a shift toward where heat is produced

Stress 3: Temperature What occurs when the temperature is increased in a system at equilibrium at constant pressure? 1. The rate of the forward reaction increases, and the rate of the reverse reaction decreases. 2. The rate of the endothermic reaction increases. 3. The rate of the forward reaction decreases, and the rate of the reverse reaction increases. 4. The rate of the exothermic reaction decreases.

Stress: Temperature Given the equilibrium reaction in a closed system as shown: What will be the result of an increase in temperature? 1. The equilibrium will shift to the left and [H 2 ] will increase. 3. The equilibrium will shift to the right and [HI] will increase. 2. The equilibrium will shift to the left and [H 2 ] will decrease. 4. The equilibrium will shift to the right and [HI] will decrease.

Le Chatelieres Principle Given the reaction at equilibrium:... (see image) Which change will cause the equilibrium to shift? 1. increase in pressure 3. addition of heat 2. increase in volume 4. addition of a catalyst

Le Chatelieres Principle Given the reaction at equilibrium (see image): The concentration of A(g) can be increased by 1. lowering the temperature 3. increasing the concentration of AB(g) 2. adding a catalyst 4. increasing the concentration of B(g)

Le Chatelieres Principle Given the reaction at equilibrium:... (see image) Which change will shift the equilibrium to the right? 1. increasing the temperature 3. decreasing the amount of SO 2 (g) 2. increasing the pressure 4. decreasing the amount of O 2 (g)