Chapter 15 Chemical Equilibrium Flashcards
Define Dynamic Equilibrium
Processes that proceed in both the forward and reverse direction are said to be reversible
Dynamic Equilibrium is the condition in which the _______ of the __________ reaction equals the _________ of the ___________ reaction
Rate; forward; rate; reverse
During Dynamic Equilibrium does the concentrations of reactants and products continue to change?
No, the concentrations of reactants and products no longer change
T/F Because reactants and products are in Dynamic Equilibrium they have equal concentrations
False; being in Dynamic Equilibrium does not mean concentrations of reactants/products are equal
Define Equilibrium Constant
The ratio of the equilibrium concentrations of the products raised to their stoichiometric coefficients and divided by the equilibrium concentrations of the reactants raised to their stoichiometric coefficients
Equilibrium Constant is represented by the letter:
“K”
When calculating Equilibrium Constants does the product or reactant go on the top?
Products go on the top and reactants go on the bottom
Express the Equilibrium Constant for
CH3OH (g) –> CO (g) + 2H2 (g)
K = [CO][H2]^2 / [CH3OH]
Express the Equilibrium Constant for
2N2O5 (g) –> 4NO2 (g) + O2 (g)
K = [NO2]^4[O2] / [N2O5]^2
Define Homogeneous Equilibria
Equilibria in which products and reactants are all in the same phase
Define Heterogeneous Equilibria
Equilibria in which products and reactants are all in different phases
When expressing Equilibrium Constants which phases do you ONLY consider?
Gas and aqueous
When expressing Equilibrium Constants which phases do you NOT consider and why?
Solids and liquids are not included in Equilibrium Constants because their concentrations do not change during reactions
Express the Equilibrium Constant for
C (s) + 2H2 (g) –> CH4 (g)
K = [CH4] / [H2]^2
Express the Equilibrium Constant for
2CO (g) –> CO2 (g) + C (s)
K = [CO2] / [CO]^2
Express the Equilibrium Constant for
CO2 (g) + H2O (l) –> H+ (aq) + HCO3- (aq)
K = [H+][HCO3-] / [CO2]
Which of the following statements is false
I) When K>1, forward reactions are favored
II) When K<1, reverse reactions are favored and forward reactions do not proceed to a great extent
III) When K=1, neither forward or reverse reactions are strongly favored
IV) K>1, implies that the reaction is very fast at producing products
IV
Define Large K (K>1)
When there are more products than reactants at equilibrium
Define Small K (K<1)
When there are more reactants than products at equilibrium
Large K means __________ reaction is favored; small K means ___________ reaction is favored
Forward; reverse
What are the 3 techniques to solve for K (Equilibrium Constant)
- Reverse and invert
- Multiply and raise
- Add more chemical equations
Define K Constant technique Reverse and Invert
If you reverse the equation, you must invert the equilibrium
Define K Constant technique Multiply and Raise
If you multiply the coefficients in the equation by a factor, you must raise the equilibrium constant to that same factor
Define K Constant technique Add More Chemical Equations
If you add 2 or more individual chemical equations to obtain an overall equation, multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant
The Equilibrium Constant For A (g) –> B (g) is 10. A reaction mixture initially contain [A] = 1.1 M and [B] = 0.00 M. Which is true at equilibrium?
I) Reaction mixture contains [A] = 1.0 M and [B] = 0.1 M
II) Reaction mixture contains [A] = 0.1 M and [B] = 1.0 M
III) Reaction mixture contains equal concentrations of A and B
II) The reaction mixture contains [A] = 0.1 M and [B] = 1.0 M because K = [B] / [A] ; K = 1.0 / 0.1 = 10
The following equation
2H2S (g) –> 2H2 (g) + S2 (g) ; kP = 2.4x10^-4
New equation
2H2 (g) + S2 (g) –> 2H2S (g) ; kP = ???
Which equation favors products and which equation favors reactants
Reverse = 1 / Kc
Reverse = 1 / 2.4x10^-4
Original equation: favors reactants
New equation: favors products
For gaseous reactions we can express the Equilibrium Constant as a ratio of ______________ or ___________ _____________
Concentrations ; partial pressures
Write out an Equilibrium Constant represented in both ratio ways (concentration and partial pressure) and explain both
I) Kc = [C]^c[D]^d / [A]^a[B]^b; the Equilibrium Constant with respect to concentration in molarity (M)
II) Kp = PC^cPD^d / PA^aPB^b; the Equilibrium Constant with respect to partial pressures in atmospheres (atm)
Solve the Equilibrium Constant for the following equation in both ratio ways (concentration and partial pressure)
2SO3 (g) –> 2SO2 (g) + O2 (g)
I) Concentration: Kc = [SO2]^2[O2] / [SO3]^2
II) Partial Pressure: Kp = (PSO2)^2(PO2) / (PSO3)^2
What is the equation showing the relationship between Kp and Kc?
Kp = Kc (RT)^Delta n
In this equation Kp = Kc (RT)^Delta n, what does Delta n represent?
C + D - (A + B); ONLY for gases
In which of the following will reactants Kc = Kp?
I) 2N2 (g) + O2 (g) –> 2N2O (g)
II) 4NH3 (g) + 3O2 (g) –> 2N2 (g)
III) 2SO2 (g) + O2 (g) –> 2SO3 (g)
IV) SO3 (g) + NO (g) –> SO2 (g) + NO2 (g)
V) None of the above
IV
Equilibrium constants depend on ___________ and DOES NOT depend on _________ _____________
Temperature; initial concentrations
Equilibrium concentrations of reactants and products depend on _________ ____________
Initial concentrations
For CO (g) + Cl2 (g) –> COCl2 (g) ; kP = 15.0 at 300 degrees celsius. Find the kC for the reaction at the same temperature
Kp = Kc (RT) ^ Delta n Kc = Kp / (RT) ^ Delta n Kc = 15.0 / (0.08206)(573.15)^-1
Define Reaction Quotient (Q)
The concentration ratio (at any point of the reaction) of the products raised to the power of their coefficients to the reactions raised to the power of their coefficients
Reaction Quotient (Q) is the same form as ___, but at ________ state, while ___ is at _____________
K; current; K; equilibrium
T/F The Reaction Quotient (Q) can have many different values, whereas Equilibrium Constant (K) can only have one value
True
At what point does Reaction Quotient (Q) and Equilibrium Constant (K) equal to one another?
At equilibrium
The value of Q relative to K is a measure of what?
The progress of the reaction toward equilibrium
What does it mean when Q = K?
It means the reaction is at equilibrium
T/F K always goes towards Q
False; Q always goes towards K because the reaction always proceeds toward equilibrium
What does it mean if Qc < Kc?
The reaction moves to the right, reactant concentration decreases while product concentration increases and Qc becomes larger
What does it mean if Qc > Kc?
The reaction moves to the left, reactant concentration increases while product concentration decreases and Qc becomes smaller
Which of the following is true
I) Q < K, reverse reaction will proceed to form more reactants
II) Q > K, forward reaction will proceed to form more products
III) Q = K, reaction is at equilibrium
IV) All of the above
V) None of the above
III
What must a ratio (x) be in order to be valid?
Less than 0.05 (5%)
What are the 3 ways to solve for X?
I) Assume X is small
II) Quadratic Equation
III) Taking square root
Define Le Chatelier’s Principle
When a chemical system at equilibrium is disturbed, so the system shifts in a direction that minimizes the disturbance trying to restore equilibrium
According to Le Chatelier’s Principle what are some disturbances to a chemical system at equilibrium?
I) Adding a reactant/product
II) Removing a reactant/product
III) Changing the volume/pressure of the reaction
IV) Changing the temperature of the reaction
If an equilibrium is disturbed by adding a reactant, which way will the reaction shift?
The reaction will shift to the right to reestablish equilibrium
If before adding a reactant to a chemical system at equilibrium was Q = K, what is it after adding a reactant?
Q < K
If an equilibrium is disturbed by adding a product, which way will the reaction shift?
The reaction will shift to the left to reestablish equilibrium
What happens to “K” when a chemical system at equilibrium has been disturbed?
K remains the same
If before adding a product to a chemical system at equilibrium was Q = K, what is it after adding a product?
Q > K
If a reactant or product is removed from a chemical system at equilibrium what occurs?
The equilibrium shifts away from the side with added chemicals and toward the side with removed ones
If before removing a reactant from a chemical system at equilibrium was Q = K, what is it after removing a reactant?
Q > K, reaction moves to the left
If before removing a product from a chemical system at equilibrium was Q = K, what is it after removing a product?
Q < K, reaction moves to the right
What is the effect of adding more CaO (s) to the mixture below?
CaCO3 (s) –> CaO (s) + CO2 (g)
No effect because CaO is a solid
What is the effect of adding more H2S (g) to the mixture below?
2H2S (g) + 3O2 (g) –> 2H2O (g) + 2SO2 (g)
The reaction will shift more in the direction of the products in order to reestablish equilibrium
Predict whether the reaction will shift left, right, or remain unchanged to the mixture below
2KClO3 (s) –> 2KCl (s) + 3O2 (g)
I) O2 is removed from the reaction mixture
II) KCl is added to the reaction mixture
III) KClO3 is added to the reaction mixture
IV) O2 is added to the reaction mixture
I) Shift to the right Q < K
II) No reaction
III) No reaction
IV) Shift to the left Q > K
Volume changes only affect what type of phase reaction?
Gas phase
Pressure and volume are ___________ related
Inversely
What happens to a reaction if there is a change in volume or a change in pressure?
The reaction shifts to minimize the pressure change
How do you determine what direction a reaction will move in?
Sum and compare the mol particles on both sides of the reaction
What happens to a gas phase reaction if volume decreases?
Pressure will increase and the reaction will shift to the side with fewer gas molecules to decrease pressure
What happens to a gas phase reaction if volume increases?
Pressure will decrease and the reaction will shift to the side with more gas molecules to increase pressure
What happens if a reaction has an equal number of moles of gas on both sides of the reaction?
A change in volume will then have no effect on the equilibrium
What happens if you add an inert gas at a fixed volume to the mixture of a gas phase reaction?
It will have no effect on the equilibrium
Define Exothermic Reaction
Heat is released; consider heat as a product
What occurs to a chemical reaction when you raise temperature in terms of Exothermic reactions?
Raising temperature (adding heat aka product) will cause a reaction to shift left, having a smaller K
What occurs to a chemical reaction when you lower temperature in terms of Exothermic reactions?
Lowering temperature (removing heat aka product) will cause a reaction to shift right, having a bigger K
Define Endothermic Reaction
Heat is absorbed; consider heat as a reactant
What occurs to a chemical reaction when you raise temperature in terms of Endothermic reactions?
Raising temperature (adding heat aka reactant) will cause a reaction to shift right, having a bigger K
What occurs to a chemical reaction when you lower temperature in terms of Endothermic reactions?
Lowering temperature (removing heat aka reactant) will cause a reaction to shift left, having a smaller K
What happens if the reaction mixture is heated in the mixture below
2KClO3 (s) –> 2KCl (s) + 3O2 (g) ; Delta(H) < 0
Reaction will shift left because it is an exothermic reaction
Decomposition of NH4HS is Endothermic
NH4HS (s) –> NH3 (g) + H2S (g)
What change must happen to an equilibrium mixture of this reaction for more H2S?
An increase in temperature
Which direction will the reaction below shift toward if the volume of the reaction mixture is decreased
2KClO3 (s) –> 2KCl (s) + 3O2 (g)
Reaction will shift to the left because decreasing volume leads to increasing pressure and it shifts towards the side with fewer moles of gas particles
The reaction below is Exothermic, which change will shift the equilibrium to the left?
2SO2 (g) + O2 (g) –> 2SO3 (g)
Raising the temperature
What is the effect of adding helium gas (constant volume) to an equilibrium mixture of the following reaction
CO (g) + Cl2 (g) –> COCl2 (g)
The reaction does not shift in either direction, no effect
