AP Chem Chapter 12 Notes: Gaseous Equilibrium Equilibrium I.
Equilibrium is reached when both the ______________ and ________________ reactions are occurring at ____________________________. A. Dynamic Equilibrium: ________ reactions are still occurring but the _________________________ of reactants are __________________. Example: 2NO2(g) ⇄ N2O4(g) B. When the reaction starts, the following happen simultaneously: 1. __________________ concentration ____________________ 2. __________________ reaction rate _____________________ 3. __________________ concentration ____________________ 4. __________________ reaction rate _____________________ C. As equilibrium is reached, the degree at which the _____________________________ (rate of the reaction) ____________________. D. Once equilibrium is reached: 1. all __________________________________________ 2. forward and reverse reactions are still occurring at a _________________________________________ 3. all __________________________________________________ E. Equilibrium is shown using a __________________________: ___________________. Both reactions are being carried out.
II.
More about equilibrium A. Equilibrium can be reached from ____________________________________. B. If the reaction starts with all products_________________________, _______________________, or a ______________________________, the ratio of products and reactants will remain _______________.
C.
Many reactions are ________________________ 1. _________________________________ ____________________________ a salt 2. Transfer of ___________________ in _______________________ 3. Transfer of _____________________ in __________________ reactions. 4. Biology: binding of ________________________________ or molecules binding ________________________________________________ 5. Environment: transfer of ______________ between the atmosphere and biosphere or transfer of dissolved ______________________ between atmosphere and hydrosphere Page 1 of 7
Equilibrium Constant (________) I.
Rate Laws (Example reaction: ______________________________) A.
Rate law of forward rxn:
B.
Rate law of reverse rxn:
C.
at equilibrium, ______________________ , therefore 1. 2. After rearranging: 3. The _______________________________________ at a certain temperature is the __________________________________________ at that temperature:
II.
For the reaction: A.
the equilibrium constant expression is:
B.
Equilibrium expression notes: 1.
Pure ___________ and _____________ are _________________________________________ _____________________________
2.
Use ______________________ or __________________________ to write the expression (keq) a. b. c. d.
C.
_____ for ____________________ (all gases-use _______________________) _____ for ____________________ [solutions-use _______________________] _____ and _____ for _________________________ _____ for ___________________________________________
3.
In general, it’s written as ______________________________________, but what is considered the products and reactants is ________________________.
4.
Remember, ____________________________________________________!!!
Examples: Write the equilibrium expressions for the following:
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III.
Calculating using the expression A. For every reaction, write the ______________________________________. B. What is ______________? What are you ___________________________? C. Plug in _______________ to find the unknown. D. Be careful with ______________________. E. Important notes: 1. K of the forward reaction is equal to the reciprocal of the reverse reaction.
2. If the coefficients are changed, the exponents change!
3. The Keq for a multistep reaction is the product of the constants of the individual steps!!!
4. Example: Given the reactions determine the value of Kc for the reaction.
IV.
Relating kc to kp A. Recall: Concentration is ______________ or ___________ B.
Use ___________________ to relate them
C.
If ________________________ of gaseous reactants and products (in the equation) and ______________________ does not change, kc will be _____________ kp
D.
Plugging in pv= nrt into kc and kp, gives
where Δn =(moles of gaseous __________________) - (moles of gaseous _____________________) Page 3 of 7
V.
Reaction quotient, q A.
Obtained by plugging in _______________________________________________ into the expression.
B.
Used to predict the direction of the reaction. 1. if __________, the system is at __________________________ 2. If __________, the reaction will shift from ____________________ because the amount of products is too ____________ and the amount of reactants is too _____________. 3. If __________, the reaction will shift from ____________________ because the amount of reactants is too _____________ and the amount of products is too ____________.
C.
At 448°C the equilibrium constant Kc for the reaction is 50.5. Predict in which direction the reaction will proceed to reach equilibrium at 448°C if we start with 2.0 × 10–2 mol of HI, 1.0 × 10–2 mol of H2, and 3.0 × 10–2 mol of I2 in a 2.00-L container.
D.
Example: At 1000 K the value of Kp for the reaction is 0.338.
Calculate the value for Qp , and predict the direction in which the reaction will proceed toward equilibrium if the initial partial pressures are
VI.
Finding equilibrium concentrations: A. Sometimes the given cannot be plugged into the equilibrium constant expression. B. The _____________________ 1. i = _________________; c=________________; e=__________________________ 2. To find _____________________ reactant is used or product is formed. 3. the “change” row maintains __________________________________________
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C.
Example: A closed system initially containing 1.000 × 10–3 M H2 and 2.000 x 10–3 M I2 at 448°C is allowed to reach equilibrium. Analysis of the equilibrium mixture shows that the concentration of HI is 1.87 × 10– 3 M. Calculate Kc at 448°C for the reaction taking place, which is
D.
Sulfur trioxide decomposes at high temperature in a sealed container: 2 SO3(g) ⇋ 2 SO2(g) + O2(g) Initially, the vessel is charged at 1000 K with SO3(g) at a partial pressure of 0.500 atm. At equilibrium the SO3 partial pressure is 0.200 atm. Calculate the value of Kp at 1000 K.
E.
A 1.000-L flask is filled with 1.000 mol of H2 and 2.000 mol of I2 at 448°C. The value of the equilibrium constant Kc for the reaction belowat 448°C is 50.5. What are the equilibrium concentrations of H2 , I2 , and HI in moles per liter?
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Le Chatelier’s Principle I.
If a system is _________________ by a change in _____________________, ______________________, or ________________________, the system will ___________________________________________ position to ___________________________ the disturbance
II.
See-Saw model:
III.
A.
Depending on what is done, the see-saw will be ________________________ and the system will shift to a certain direction to ________________________ equilibrium.
B.
Equilibrium shifts away from what is ____________ and towards what is ___________________. 2 NO2 (g) ⇋ N2O4 (g)
Example of change in concentration: Change to System
“Heavy” Side of See-Saw
Equil. Shift
∆H = -57.2 kJ By...
Add NO2 Add N2O4 Remove NO2 IV.
Example of change in temperature:
Change to System
2 NO2 (g) ⇋ N2O4 (g)
“Heavy” Side of See-Saw
Equil. Shift
∆H = -57.2 kJ
By...
Decrease temp. Increase temp.
V.
A.
Changing ____________________________________! This is because concentration and pressure are ______________________________.
B.
Treat energy as a product or a reactant to determine equilibrium shift.
Example of change in pressure:
2 NO2 (g) ↔ N2O4 (g)
∆H = -57.2 kJ
A.
Only applies to _______________!!!
B.
Increasing pressure favors the side with ____________________________________________, so the equilibrium position shifts that direction (___________, producing N2O4 and heat). Count ______________________ of gas particles!
C.
Decreasing pressure favors side with ___________________________________________________ (____________, producing NO2 and absorbing heat).
D.
Volume has the ____________________________ since it is ______________ proportional to pressure. Page 6 of 7
V.
Catalysts: lowers the ____________________________________ of a reaction. A.
This affects the ______________________________.
B.
Therefore, adding a catalyst does not affect equilibrium position, thus... 1. ______________________ will occur 2. But, the ____________ it takes to reach _____________________________________!
VII.
VIII.
Inert gases: A.
Inert means that it is _______________________, so they are _____________________ in the reaction.
B.
They will not affect reaction so nothing will happen to the ________________________________ or ________________________________.
Addition of acids/bases: A.
Strong acids and bases ___________________________ resulting in _____ (or _________)and ______________, respectively.
B.
These ions will _____________________________________________ if it is present in the equation.
C.
Example: 6m nitric acid is added to the following:
NH3 + H2O ⇋ NH4+ + OH-
1. ____________ reacts with _________, causing the ___________________ of it. 2. Reaction shifts to the ____________, creating more ____________________________. 3. Same goes for substances that result in ________________________.
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