Chapter 15 Chemical Equilibrium Flashcards by Serena Saechia

Define Dynamic Equilibrium

Processes that proceed in both the forward and reverse direction are said to be reversible

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Dynamic Equilibrium is the condition in which the _______ of the __________ reaction equals the _________ of the ___________ reaction

Rate; forward; rate; reverse

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During Dynamic Equilibrium does the concentrations of reactants and products continue to change?

No, the concentrations of reactants and products no longer change

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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

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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

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Equilibrium Constant is represented by the letter:

“K”

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When calculating Equilibrium Constants does the product or reactant go on the top?

Products go on the top and reactants go on the bottom

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Express the Equilibrium Constant for

CH3OH (g) –> CO (g) + 2H2 (g)

K = [CO][H2]^2 / [CH3OH]

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Express the Equilibrium Constant for

2N2O5 (g) –> 4NO2 (g) + O2 (g)

K = [NO2]^4[O2] / [N2O5]^2

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Define Homogeneous Equilibria

Equilibria in which products and reactants are all in the same phase

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Define Heterogeneous Equilibria

Equilibria in which products and reactants are all in different phases

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When expressing Equilibrium Constants which phases do you ONLY consider?

Gas and aqueous

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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

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Express the Equilibrium Constant for

C (s) + 2H2 (g) –> CH4 (g)

K = [CH4] / [H2]^2

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Express the Equilibrium Constant for

2CO (g) –> CO2 (g) + C (s)

K = [CO2] / [CO]^2

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Express the Equilibrium Constant for

CO2 (g) + H2O (l) –> H+ (aq) + HCO3- (aq)

K = [H+][HCO3-] / [CO2]

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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

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Define Large K (K>1)

When there are more products than reactants at equilibrium

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Define Small K (K<1)

When there are more reactants than products at equilibrium

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Large K means __________ reaction is favored; small K means ___________ reaction is favored

Forward; reverse

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What are the 3 techniques to solve for K (Equilibrium Constant)

Reverse and invert
Multiply and raise
Add more chemical equations

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Define K Constant technique Reverse and Invert

If you reverse the equation, you must invert the equilibrium

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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

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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

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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

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

Chapter 15 Chemical Equilibrium Flashcards

(79 cards)