“Equilibrium”  What does it mean?  What word does it look like?  What does it mean?  What word does it look like?

Aim: How can we look at systems at equilibrium?  Equilibrium: a state of balance  Dynamic Equilibrium: when overall rates of forward and reverse reactions are equal  This is a Reversible Equilibrium and is indicated by a double arrow  Equilibrium: a state of balance  Dynamic Equilibrium: when overall rates of forward and reverse reactions are equal  This is a Reversible Equilibrium and is indicated by a double arrow

Physical Equilibrium  Physical Equilibrium is balance in physical processes  Phase equilibrium: equilibrium between phases  Physical Equilibrium is balance in physical processes  Phase equilibrium: equilibrium between phases

Solution Equilibrium  Solution Equilibrium: dissolving & crystallization happening at equal rate liquid-gas liquid-solid

Chemical Equilibrium  CH 4 (g) + H 2 O (g)  3 H 2 (g) + CO (g)

Chemical Equilibrium  CH 4 (g) + H 2 O (g)  3 H 2 (g) + CO (g)

Homework  Finish equilibrium review pages

Remember: Equilibrium is Stability  CH 4 + H 2 O  3 H 2 + CO  Fwd rxn rate = Rev Rxn rate  Using up reactants to make products  CH 4 + H 2 O  3 H 2 + CO  Fwd rxn rate = Rev Rxn rate  Using up reactants to make products

How will a closed system react when a stress if applied? equilibrium stress new equilibrium

Le Chatelier’s Principle  Closed systems will adjust to balance stresses  Concentration, temperature, pressure  Shifts are increased reaction rates in either Fwd (right→) or Rev (left←) directions  Closed systems will adjust to balance stresses  Concentration, temperature, pressure  Shifts are increased reaction rates in either Fwd (right→) or Rev (left←) directions

Concentration  Pen/pencil trick, pointing towards shift A + B  C  Add-Away, Take-Towards  Pen/pencil trick, pointing towards shift A + B  C  Add-Away, Take-Towards

 UV455zFs

Concentration  Add-Away

Concentration  Take-Towards

Le Chatelier’s Principle: Temperature  Treat “heat/energy” like any other reactant  Adding heat favors reaction  Removing heat favors reaction  Treat “heat/energy” like any other reactant  Adding heat favors reaction  Removing heat favors reaction

N H 2  2 NH kJ

12.6 kJ + H 2 + I 2  2 HI

Do Now: Answer the following questions  1. What is Le Chatelier’s Principle?  2. Label the forward and reverse reactions as endothermic or exothermic: CO (g) + 3 H 2  CH 4 (g) + H 2 O (g) + heat  3. In which direction will equilibrium shift if the temperature is increased?  4. In which direction will equilibrium shift if the temperature is decreased?  1. What is Le Chatelier’s Principle?  2. Label the forward and reverse reactions as endothermic or exothermic: CO (g) + 3 H 2  CH 4 (g) + H 2 O (g) + heat  3. In which direction will equilibrium shift if the temperature is increased?  4. In which direction will equilibrium shift if the temperature is decreased?

Pressure  Only for gases; count # of molecules on each side  If # is equal,  pressure has no effect   pressure shifts towards fewer molecules   pressure shifts towards more molecules  Only for gases; count # of molecules on each side  If # is equal,  pressure has no effect   pressure shifts towards fewer molecules   pressure shifts towards more molecules

Pressure Example  4 NH (g) + 5 O 2 (g)  4 NO (g) + 6 H 2 O (g) = gas molecules = gas molecules  Increase pressure: shift (more to less) 9 10  Decrease pressure: shift (less to more) 9 10  4 NH (g) + 5 O 2 (g)  4 NO (g) + 6 H 2 O (g) = gas molecules = gas molecules  Increase pressure: shift (more to less) 9 10  Decrease pressure: shift (less to more) 9 10

N H 2  2 NH 3 Equilibrium shift [N 2 ] [H 2 ] [NH 3 ] # molecules: Increased pressure shifts towards fewer molecules Decreased pressure shifts towards more molecules

H 2 + I 2  2 HI Equilibrium shift [H 2 ] [I 2 ] [HI] # molecules: Increased pressure shifts towards fewer molecules Decreased pressure shifts towards more molecules

Conclusion Questions  1. How does a system at equilibrium respond to a stress? List the factors that can be stresses on an equilibrium system.

Conclusion Questions  2. Given the reaction at equilibrium: N 2 (g) + 3 H 2 (g)  2 NH 2 (g) + heat  Which stress would cause the equilibrium to shift to the left?  (a) Increasing the temperature  (b) Adding N 2 (g) to the system  (c) Adding H 2 (g) to the system  2. Given the reaction at equilibrium: N 2 (g) + 3 H 2 (g)  2 NH 2 (g) + heat  Which stress would cause the equilibrium to shift to the left?  (a) Increasing the temperature  (b) Adding N 2 (g) to the system  (c) Adding H 2 (g) to the system

Conclusion Questions  2. Given the reaction at equilibrium: N 2 (g) + O 2 (g)  2 NO (g)  If the concentration of N 2 (g) is increased, the concentration of O 2 (g) will  (a) Decrease  (b) Remain the same  (c) Increase  2. Given the reaction at equilibrium: N 2 (g) + O 2 (g)  2 NO (g)  If the concentration of N 2 (g) is increased, the concentration of O 2 (g) will  (a) Decrease  (b) Remain the same  (c) Increase