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Equilibrium Big name-- easy idea!

Chemical Reactions You have a system made up of a bunch of molecules. Energy is absorbed to break bonds. Molecules combine to form new compounds (releasing energy).

Collision Theory Molecules must bang together— with enough energy (activation energy) in the right orientation (just the right way) for a reaction to occur

Potential Energy Diagram Ea = activation energy. This is the minimum amount of energy necessary to make the reaction happen. Top of the hill Activated complex- (transition state)

Reverse Reactions Once you have a bunch of the new compound ………the new compound wants to go back to being the old compound.

In short- the products become reactants and have to find a way to get back up over the hill

Put those two ideas together and you have EQUILIBRIUM 1. Reactants combine to make a products. 2. Products like to break apart and turn back into the reactants. 3. There is a point where the two reactions happen and you can't tell that any reactions are occurring (equilibrium).

Think about a swimming pool. (Phase Changes) What happens in the summer when it is really hot? What happens when it is raining? What is happening when the level of the water doesn’t change?

In a closed system… 1.Net transfer of molecules from the liquid state to the vapor state 2.The amount of the substance in the vapor state becomes constant 3.The equilibrium state is achieved.

Rate of Reaction Depends on the properties of the reactants (size and reactivity) Depends on the conditions of the system

Factors affecting Reaction Rate Write about how each affects the kinetic energy of the reactants. 1.Temperature 2.Concentration 3.Particle Size (surface area) 4.Agitation

Iodine/ Vit C demo

Particle Size Demo

So.. What exactly is equal at equilibrium?? Rate forward rxn = Rate reverse rxn Law of Chemical Equilibrium There is no net change in the actual amount of the compounds. Be careful!! The rate is equal– the amount is probably not equal!!

Changes with time in the rates of reactions. This looks the same no matter what the products and reactants are!!

Equilibrium Position The equilibrium position indicates the relative concentration of the products and reactants at equilibrium. A + B -----> AB Can also be the reverse reaction. AB -----> A + B We draw a wacky double arrow shows to show what side of the equation is favored (has more). A + B AB Size Matters!!

LeChatelier’s Principle If a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction will reduce the change.

Things we can mess with-- Concentration- if a component is added to a reaction system at equilibrium, the equilibrium position will shift in the direction that lowers the concentration of that component. If a component is removed, the opposite happens. H 2 + F > 2HF Add this  get more of this get more of this  Add this

Temperature Treat energy as a reactant in an endothermic reaction and a product in an exothermic reaction. Predict the direction of the shift in the same way as when an actual product or reactant is added. 2H 2 + O 2  2H 2 O + 483kJ

Pressure- only matters with gasses! 2SO 2(g) + O 2(g)  2SO 3(g)

Volume How about changing the volume of the container?? Decreasing the volume of the reaction container will cause the equilibrium to shift towards the side of the reaction with the fewest number of gas molecules.

Demo

Equilibrium Constant Equilibrium Expression: Is a ratio of the rates of reaction. aA + bB cC + dD K eq = [C] c [D] dor [Products] [A] a [B] b [Reactants]

State of Matter– does matter Reactants or products that are solids (s) or liquids (l) are not put into the equilibrium expression ONLY gasses (g) and aqueous solns (aq) Are included in the equilibrium expression!!

Let’s Practice! Write the equilibrium expression for the following reactions. a.H 2 + F 2 2HF b.N 2 + 3H 2 2NH 3

Answers a.H 2 + F 2 2HF K eq = [HF] 2 [H 2 ] [F 2 ] b. N 2 + 3H 2 2NH 3 K eq = [NH 3 ] 2 [N 2 ] [H 2 ] 3

Example- Write the equilibrium expression CaCO 3 (s) + Heat  -  CaO (l) + CO 2(g)

What does K eq tell us?? It tells us which side of the equation is favored (will we get more products or reactants?). K eq >1 Products favored, Spontaneous K eq <1 Reactants favored, Nonspontaneous

Here- watch this!! om/petrucci/medial ib/media_portfolio/ text_images/066_L eChateliersPr.MOV