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Questions and Answers
For a reaction at equilibrium, if the rate of the forward reaction increases, what change must occur in the reverse reaction?
For a reaction at equilibrium, if the rate of the forward reaction increases, what change must occur in the reverse reaction?
- The rate of the reverse reaction must decrease until it ceases completely.
- The rate of the reverse reaction must also increase until it equals the rate of the forward reaction. (correct)
- The rate of the reverse reaction will fluctuate randomly, with no predictable pattern.
- The rate of the reverse reaction will remain constant, unaffected by the change in the forward reaction.
Consider the reaction $aA + bB \rightleftharpoons cC + dD$. How is the equilibrium constant expression, $K_c$, formulated?
Consider the reaction $aA + bB \rightleftharpoons cC + dD$. How is the equilibrium constant expression, $K_c$, formulated?
- $K_c = \frac{[cC]^c[dD]^d}{[aA]^a[bB]^b}$ (correct)
- $K_c = \frac{[aA]^a[bB]^b}{[cC]^c[dD]^d}$
- $K_c = [aA]^a[bB]^b[cC]^c[dD]^d$
- $K_c = \frac{[aA][bB]}{[cC][dD]}$
What condition is necessary to calculate the value of $K_c$ from known equilibrium amounts?
What condition is necessary to calculate the value of $K_c$ from known equilibrium amounts?
- The volume of the reaction vessel must be exactly 1 liter.
- The equilibrium amounts must be expressed in molar concentrations. (correct)
- The reaction must be at standard temperature and pressure.
- The reaction must involve only gaseous reactants and products.
Consider the reversible reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$. If, at equilibrium, the partial pressures are $P_{N_2} = 2 atm$, $P_{H_2} = 3 atm$, and $P_{NH_3} = 4 atm$, what is the value of $K_p$?
Consider the reversible reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$. If, at equilibrium, the partial pressures are $P_{N_2} = 2 atm$, $P_{H_2} = 3 atm$, and $P_{NH_3} = 4 atm$, what is the value of $K_p$?
At 700 K, the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ has an equilibrium constant $K_c = 4.2 \times 10^5$. If the reaction mixture contains [SO₂] = 0.20 M, [O₂] = 0.25 M, and [SO₃] = 85 M, which direction will the reaction proceed to reach equilibrium?
At 700 K, the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ has an equilibrium constant $K_c = 4.2 \times 10^5$. If the reaction mixture contains [SO₂] = 0.20 M, [O₂] = 0.25 M, and [SO₃] = 85 M, which direction will the reaction proceed to reach equilibrium?
In the reaction $CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$, what change will occur if the volume of the container is decreased?
In the reaction $CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$, what change will occur if the volume of the container is decreased?
Given the endothermic reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, what effect will increasing the temperature have on the value of $K_c$?
Given the endothermic reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, what effect will increasing the temperature have on the value of $K_c$?
Consider the equilibrium: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ If at equilibrium, some $O_2$ is added to the system, what will happen to the amount of $SO_3$?
Consider the equilibrium: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ If at equilibrium, some $O_2$ is added to the system, what will happen to the amount of $SO_3$?
Given the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, with $K_c = 50$ at a certain temperature. If a reaction vessel initially contains [Hâ‚‚] = 0.2 M, [Iâ‚‚] = 0.2 M, and [HI] = 0.0 M, what will happen initially in order for said reaction to obtain equilibrium?
Given the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, with $K_c = 50$ at a certain temperature. If a reaction vessel initially contains [Hâ‚‚] = 0.2 M, [Iâ‚‚] = 0.2 M, and [HI] = 0.0 M, what will happen initially in order for said reaction to obtain equilibrium?
For the reaction $A(g) + B(g) \rightleftharpoons C(g)$, the equilibrium constant $K_c$ is 4. If the initial concentrations are [A] = 2 M, [B] = 2 M, and [C] = 0 M, what is the equilibrium concentration of C?
For the reaction $A(g) + B(g) \rightleftharpoons C(g)$, the equilibrium constant $K_c$ is 4. If the initial concentrations are [A] = 2 M, [B] = 2 M, and [C] = 0 M, what is the equilibrium concentration of C?
How does a catalyst affect a reaction at equilibrium?
How does a catalyst affect a reaction at equilibrium?
What is the molar composition of the equilibrium mixture? $PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)$. Initially 1.00 mol $PCl_5$ in a 1.00-L container, and at equilibrium 0.135 mol $PCl_3$.
What is the molar composition of the equilibrium mixture? $PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)$. Initially 1.00 mol $PCl_5$ in a 1.00-L container, and at equilibrium 0.135 mol $PCl_3$.
Methanol is commercially made by $2H_2(g) + CO(g) \rightleftharpoons CH_3OH(g)$. What is the $K_c$ expression for this reaction?
Methanol is commercially made by $2H_2(g) + CO(g) \rightleftharpoons CH_3OH(g)$. What is the $K_c$ expression for this reaction?
Carbon dioxide decomposes at elevated temperature by $2CO_2(g) \rightleftharpoons 2CO(g) + O_2(g)$. At 3000 K, 2.00 mol $CO_2$ placed in 1.00-L container, at equilibrium, 0.90 mol $CO_2$ remains. What is the value of $K_c$ at this temperature?
Carbon dioxide decomposes at elevated temperature by $2CO_2(g) \rightleftharpoons 2CO(g) + O_2(g)$. At 3000 K, 2.00 mol $CO_2$ placed in 1.00-L container, at equilibrium, 0.90 mol $CO_2$ remains. What is the value of $K_c$ at this temperature?
Write the $K_c$ expression for the following heterogeneous reaction: $H_2O(g) + C(s) \rightleftharpoons CO(g) + H_2(g)$
Write the $K_c$ expression for the following heterogeneous reaction: $H_2O(g) + C(s) \rightleftharpoons CO(g) + H_2(g)$
Given: $aA + bB \rightleftharpoons cC + dD; K_1$. What is the $K_2$ if the reaction is reversed?
Given: $aA + bB \rightleftharpoons cC + dD; K_1$. What is the $K_2$ if the reaction is reversed?
Given: $aA + bB \rightleftharpoons cC + dD; K_1$. What is the $K_2$ if the reaction is doubled?
Given: $aA + bB \rightleftharpoons cC + dD; K_1$. What is the $K_2$ if the reaction is doubled?
How are $K_p$ and $K_c$ related? $aA(g) + bB(g) \rightleftharpoons cC(g) + dD(g)$
How are $K_p$ and $K_c$ related? $aA(g) + bB(g) \rightleftharpoons cC(g) + dD(g)$
If the value of $K_c$ at $227^\degree C$ is 0.0952 for the following reaction: $CH_3OH(g) \rightleftharpoons CO(g) + 2H_2(g)$, what is $K_p$ at this temperature?
If the value of $K_c$ at $227^\degree C$ is 0.0952 for the following reaction: $CH_3OH(g) \rightleftharpoons CO(g) + 2H_2(g)$, what is $K_p$ at this temperature?
For $K_c$ = 0.82 for a reaction, which statement best describes the composition of the equilibrium mixture?
For $K_c$ = 0.82 for a reaction, which statement best describes the composition of the equilibrium mixture?
Nickel(II) oxide reduced to the metal by $CO(g) + NiO(s) \rightleftharpoons CO_2(g) + Ni(s)$. If the partial pressure of CO is 100. mmHg and the total pressure of CO and $CO_2$ does not exceed 1.0 atm, will this reaction occur at 1500 K at equilibrium? ($K_p$ = 700. at 1500 K)
Nickel(II) oxide reduced to the metal by $CO(g) + NiO(s) \rightleftharpoons CO_2(g) + Ni(s)$. If the partial pressure of CO is 100. mmHg and the total pressure of CO and $CO_2$ does not exceed 1.0 atm, will this reaction occur at 1500 K at equilibrium? ($K_p$ = 700. at 1500 K)
Nitrogen and oxygen form nitric oxide by $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$. If an equilibrium mixture at $25^\circ C$ contains 0.040 M $N_2$ and 0.010 M $O_2$, what is the concentration of NO in this mixture? The equilibrium constant at $25^\circ C$ is $1.0 \times 10^{-30}$
Nitrogen and oxygen form nitric oxide by $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$. If an equilibrium mixture at $25^\circ C$ contains 0.040 M $N_2$ and 0.010 M $O_2$, what is the concentration of NO in this mixture? The equilibrium constant at $25^\circ C$ is $1.0 \times 10^{-30}$
Hydrogen iodide decomposes by $2HI(g) \rightleftharpoons H_2(g) + I_2(g)$. At 800 K, the equilibrium constant, $K_c$, for this reaction is 0.016. IF 0.50 mol HI placed in a 5.0-L flask, what is the composition of the equilibrium mixture in molarities?
Hydrogen iodide decomposes by $2HI(g) \rightleftharpoons H_2(g) + I_2(g)$. At 800 K, the equilibrium constant, $K_c$, for this reaction is 0.016. IF 0.50 mol HI placed in a 5.0-L flask, what is the composition of the equilibrium mixture in molarities?
$N_2O_4$ decomposes by $N_2O_4(g) \rightleftharpoons 2NO_2(g)$. At $100^\circ C$, $K_c$ = 0.36. If a 1.00-L flask initially contains 0.100 M $N_2O_4$, what will be the equilibrium concentration of $NO_2$?
$N_2O_4$ decomposes by $N_2O_4(g) \rightleftharpoons 2NO_2(g)$. At $100^\circ C$, $K_c$ = 0.36. If a 1.00-L flask initially contains 0.100 M $N_2O_4$, what will be the equilibrium concentration of $NO_2$?
Initial conditions: $H_2(g) + F_2(g) \rightleftharpoons 2HF(g)$; $K_c = 1.15 \times 10^2$. 3.000 mol of each species is put in 1.500-L vessel. What is the equilibrium concentration of each species?
Initial conditions: $H_2(g) + F_2(g) \rightleftharpoons 2HF(g)$; $K_c = 1.15 \times 10^2$. 3.000 mol of each species is put in 1.500-L vessel. What is the equilibrium concentration of each species?
The following reaction is at equilibrium: $COCl_2(g) \rightleftharpoons CO(g) + Cl_2(g)$. If chlorine gas is added to the reaction mixture what direction will the reaction shift?
The following reaction is at equilibrium: $COCl_2(g) \rightleftharpoons CO(g) + Cl_2(g)$. If chlorine gas is added to the reaction mixture what direction will the reaction shift?
The following reaction is at equilibrium: $COCl_2(g) \rightleftharpoons CO(g) + Cl_2(g)$. If carbon monoxide gas is removed from the mixture what direction will the direction shift?
The following reaction is at equilibrium: $COCl_2(g) \rightleftharpoons CO(g) + Cl_2(g)$. If carbon monoxide gas is removed from the mixture what direction will the direction shift?
In which direction will each reaction shift when the volume of the reaction container is increased?
In which direction will each reaction shift when the volume of the reaction container is increased?
If $\Delta H^\degree$ = 484 kJ for the reaction $2H_2O(g) \rightleftharpoons 2H_2(g) + O_2(g)$, would you expect this reaction to be favorable at high or low temperatures?
If $\Delta H^\degree$ = 484 kJ for the reaction $2H_2O(g) \rightleftharpoons 2H_2(g) + O_2(g)$, would you expect this reaction to be favorable at high or low temperatures?
The Fischer-Tropsch process involves $8CO(g) + 17H_2(g) \rightleftharpoons C_8H_{18}(g) + 8H_2O(g)$. Suppose the reaction is at equilibrium at 200°C, then cooled to condense the octane, and then the remaining gases are reheated to 200°C. In which direction will the equilibrium shift?
The Fischer-Tropsch process involves $8CO(g) + 17H_2(g) \rightleftharpoons C_8H_{18}(g) + 8H_2O(g)$. Suppose the reaction is at equilibrium at 200°C, then cooled to condense the octane, and then the remaining gases are reheated to 200°C. In which direction will the equilibrium shift?
A typical reaction that occurs in the Fischer–Tropsch process is $8CO(g) + 17H_2(g) \rightleftharpoons C_8H_{18}(g) + 8H_2O(g)$. In which direction will the equilibrium shift when the pressure is increased?
A typical reaction that occurs in the Fischer–Tropsch process is $8CO(g) + 17H_2(g) \rightleftharpoons C_8H_{18}(g) + 8H_2O(g)$. In which direction will the equilibrium shift when the pressure is increased?
Which statement accurately describes dynamic equilibrium in a reversible chemical reaction?
Which statement accurately describes dynamic equilibrium in a reversible chemical reaction?
For the synthesis of ammonia, $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, indicate how $K_p$ and $K_c$ are related.
For the synthesis of ammonia, $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, indicate how $K_p$ and $K_c$ are related.
For a reaction where solids or pure liquids are involved, what is their contribution to the $K_c$ expression?
For a reaction where solids or pure liquids are involved, what is their contribution to the $K_c$ expression?
Flashcards
Chemical equilibrium
Chemical equilibrium
State where forward and reverse reactions occur at equal rates.
Stoichiometry at equilibrium
Stoichiometry at equilibrium
Apply stoichiometry to determine mixture composition at equilibrium.
Equilibrium constant (Kc)
Equilibrium constant (Kc)
A ratio of products to reactants at equilibrium.
Equilibrium-constant expression
Equilibrium-constant expression
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Law of mass action
Law of mass action
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Equilibrium constant Kp
Equilibrium constant Kp
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Combining equilibrium constants
Combining equilibrium constants
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Homogeneous equilibrium
Homogeneous equilibrium
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Heterogeneous equilibrium
Heterogeneous equilibrium
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Solids/liquids in equilibrium
Solids/liquids in equilibrium
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Reaction quotient (Q)
Reaction quotient (Q)
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Comparing Q to K
Comparing Q to K
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ICE tables
ICE tables
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Le Châtelier's principle
Le Châtelier's principle
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Adding/removing reactants/products.
Adding/removing reactants/products.
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Pressure effect
Pressure effect
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Temperature effect
Temperature effect
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Effect of a catalyst
Effect of a catalyst
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Study Notes
Describing Chemical Equilibrium
- Chemical reactions often appear to stop before completion, actually, they are reversible with original reactants forming products, and products reacting to reform original reactants.
- Chemical equilibrium exists when the forward and reverse reactions occur at the same rate.
- Stoichiometry applies to compute the content of the reaction mixture at equilibrium.
Learning Objectives for Chemical Equilibrium
- Define dynamic equilibrium and chemical equilibrium.
- Apply stoichiometry to an equilibrium mixture.
The Equilibrium Constant
- The equilibrium constant expression involves multiplying product concentrations, dividing by reactant concentrations, and raising each term to the power of its coefficient.
- The equilibrium constant is the value of the expression when equilibrium concentrations are substituted.
- Equilibrium-constant expression and equilibrium constant should be defined.
- The law of mass action should be stated.
- Equilibrium-constant expressions should be written.
- Kinetics argument for the approach to chemical equilibrium should be described.
- Equilibrium constant should be obtained from reaction composition.
The Equilibrium Constant: Kp and Kc
- Kp represents the equilibrium constant described in terms of partial pressures.
- Kp and Kc are related and the formula for their relationship should be stated.
- The law of mass action should be stated.
- Kc can be obtained for a reaction written as a sum of other reactions with known Kc values.
Homogeneous vs. Heterogeneous Equilibria
- Homogeneous equilibrium consists of reactions where all reactants and products are in the same phase.
- Heterogeneous equilibrium consists of reactions where reactants and products are in more than one phase.
- Kc can be written for a reaction containing pure solids or liquids; the concentrations of pure solids and liquids are not included in the equilibrium expression.
Interpreting and Using the Equilibrium Constant
- A qualitative interpretation of the equilibrium constant can be made bases on its value.
- The reaction quotient, Q, is defined.
- The direction of a reaction can be described by comparing Q with Kc.
- The reaction quotient should be used.
- Equilibrium concentrations can be calculated.
- One equilibrium concentration can be obtained from others.
- Equilibrium problems involving linear equations in 'x' can be solved.
- Equilibrium problems involving quadratic equations in 'x' can be solved.
Predicting Reaction Direction
- The equilibrium constant value can qualitatively describe the reaction mixture content. K is very large (>10^2), the equilibrium mixture is mostly products.
- If K is very small (10^2), the equilibrium mixture is mostly products.
- If K approaches 1, the equilibrium mixture contains appreciable amounts of both reactants and products.
Reaction Quotient, Q
- Q has the same form as the equilibrium constant but uses initial concentrations; it is used to predict reaction direction.
- If Kc > Q, the reaction proceeds to the right.
- If Kc < Q, the reaction proceeds to the left.
- If Kc = Q, the reaction is at equilibrium.
- Qc must move toward Kc.
Le Châtelier’s Principle on Reactants/Products
- When a reactant or product is added or removed, it alters the equilibrium.
- Le Châtelier’s principle states that if a system in chemical equilibrium is disturbed by a change in concentration, temperature, or pressure, the system shifts to counteract the change.
- If a substance is added to the mixture, the equilibrium shifts to use it.
- If a substance is removed from the mixture, the equilibrium shifts to produce it.
- Changes in partial pressure affect equilibrium like adding/removing substances.
Le Châtelier’s Principle on Pressure
- A change in pressure occurs due to a change in the volume of the reaction container.
- Decreasing the container size increases pressure; the reaction shifts to reduce pressure, favoring the side with fewer gas molecules.
- Increasing the container size decreases pressure; the reaction shifts to increase pressure, favoring the side with more gas molecules.
- Pressure has no effect on equilibrium if both sides have equal gas moles.
Le Châtelier’s Principle on Temperature
- Changing temperature impacts the equilibrium constant value and causes a shift in equilibrium.
- For endothermic reactions (∆H° > 0), heat is considered a reactant.
- For exothermic reactions (∆H° < 0), heat is considered a product.
- Increasing temperature increases Kc for endothermic reactions, and decreases it for exothermic reactions. Decreasing temperature has the opposite effect.
- Adding heat shifts the reaction to use heat and removing heat shifts the reaction to produce heat.
Effect of a Catalyst
- Define catalyst.
- A catalyst accelerates the rate of reaction but does not alter the equilibrium.
- Describe how a catalyst can affect the product formed.
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