WU 4/23 1.How would the rate of reaction be affected by the following changes? a. Increase concentration b. Decrease temperature c. Increasing pressure (gases only) d. Adding a catalyst 2. Use collision theory to explain each answer.

WU **Take Out HW** 1. Nitrogen oxide reacts with oxygen to yield nitrogen dioxide. Write the equation for when this reaction reaches equilibrium. 2. How is chemical equilibrium defined? 3. How do the concentrations of reactants and products change at equilibrium?

1.H 2 + N 2  NH 3 ΔH = kJ/mol Predict the shift in equilibrium if: a.More N2 is added b.N2 is removed c.NH3 is added d.Temperature is increased e.Volume is increased

Equilibrium position Equilibrium does not mean 50:50. Eq. position = the relative concentrations of the products and reactants –At equilibrium are there more products or reactants? Determines whether the forward or reverse reaction is favored.

18-2 Factors Affecting Equilibrium Newton’s First Law- –an object at rest remains at rest, unless disturbed –For equilibrium- a system at equilibrium remains at equilibrium, unless the equilibrium is disturbed

18-2 Factors Affecting Equilibrium If disturbed, the system will move to counteract the disturbance. Ex: If you are pushed, you will shift your weight to try to stay on your feet.

Types of disturbances/stresses: Temperature: –liquid + energy   vapor. –If the temperature is increased what will happen? For deposition: gas  solid + energy – If temperature is increased, which direction will the reaction move

Types of Disturbances Concentration EX: School dance boys, girls, dancing couples Adding boys or girls  more dancing couples. Adding couples  more boys & girls Removing dancing couples  more couples will take their places on the floor.

Types of Disturbances Pressure: –Affects only gaseous reac. & prod. The system will respond to couteract the pressure change –It depends on the reaction. Increase in pressure = system will try to reduce pressure –Fewer gas particles –Will shift to whatever side accomplishes this.

Equilibrium Shifts due to Pressure Nitrogen reacts with hydrogen to produce ammonia. –Write a balanced chemical equation. –How many gas particles are on the left? –On the right? If the volume is decreased, how is pressure affected? Which way will the system shift to counteract the change?

Practice: H 2 + N 2  NH 3 If the volume of the reaction is increased, will the system shift to make more products or reactants? **Remember shift whichever way will counteract the pressure change**

Mixed Practice: NO + O 2  NO 2 For this reaction determine the equilibrium shift due to these changes. (Use the given sentence frame) –add reactant –remove reactant –add product –remove product –increase volume of container

Mixed Practice: liquid + energy  vapor If the temperature is decreased, will more liquid or vapor form? liquid  solid + energy If the temperature is decreased, will more liquid or solid form?