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Questions and Answers
For the reaction $aA + bB \rightleftharpoons cC + dD$, how is the reaction quotient $Q$ expressed?
For the reaction $aA + bB \rightleftharpoons cC + dD$, how is the reaction quotient $Q$ expressed?
- $Q = \frac{[aA][bB]}{[cC][dD]}$
- $Q = \frac{[A]^a[B]^b}{[C]^c[D]^d}$
- $Q = K[A]^a[B]^b$
- $Q = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ (correct)
Consider the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$. If, at a given time, $[N_2O_4] = 0.5 \text{ mol/L}$ and $[NO_2] = 1 \text{ mol/L}$, what is the value of the reaction quotient $Q$?
Consider the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$. If, at a given time, $[N_2O_4] = 0.5 \text{ mol/L}$ and $[NO_2] = 1 \text{ mol/L}$, what is the value of the reaction quotient $Q$?
- 0.5
- 2 (correct)
- 1
- 4
For the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, what is the value of Q at time equals zero?
For the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, what is the value of Q at time equals zero?
- 0 (correct)
- It cannot be determined.
- 2
- 1
At equilibrium, what is the relationship between the reaction quotient $Q_e$ and the equilibrium constant $K$?
At equilibrium, what is the relationship between the reaction quotient $Q_e$ and the equilibrium constant $K$?
Consider the reaction $A \rightleftharpoons B$. If $Q < K$, which of the following statements is true?
Consider the reaction $A \rightleftharpoons B$. If $Q < K$, which of the following statements is true?
For the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, the equilibrium constant $K$ is 2.7. If the reaction mixture contains only $NO_2$ initially, what will happen as the system approaches equilibrium?
For the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, the equilibrium constant $K$ is 2.7. If the reaction mixture contains only $NO_2$ initially, what will happen as the system approaches equilibrium?
Which statement accurately describes the effect of temperature on the equilibrium constant, $K$?
Which statement accurately describes the effect of temperature on the equilibrium constant, $K$?
What is the correct equilibrium constant expression ($K_c$) for the reaction $CH_4(g) + H_2O(g) \rightleftharpoons CO(g) + 3H_2(g)$?
What is the correct equilibrium constant expression ($K_c$) for the reaction $CH_4(g) + H_2O(g) \rightleftharpoons CO(g) + 3H_2(g)$?
Which substances are excluded from the equilibrium constant expression?
Which substances are excluded from the equilibrium constant expression?
Consider the reaction $2NaHCO_3(s) \rightleftharpoons Na_2CO_3(s) + H_2O(g) + CO_2(g)$. What is the correct expression for $K_c$?
Consider the reaction $2NaHCO_3(s) \rightleftharpoons Na_2CO_3(s) + H_2O(g) + CO_2(g)$. What is the correct expression for $K_c$?
For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, $K$ is $4.8 \times 10^{-31}$. What does this indicate about the position of the equilibrium?
For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, $K$ is $4.8 \times 10^{-31}$. What does this indicate about the position of the equilibrium?
For a certain reaction at 25°C, the value of $K$ is very large. What does this indicate about the extent of the reaction at equilibrium?
For a certain reaction at 25°C, the value of $K$ is very large. What does this indicate about the extent of the reaction at equilibrium?
Consider the equilibrium $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$. Initially, 0.100 mol of $H_2$ and 0.100 mol of $I_2$ are placed in a 1.00 L flask. At equilibrium, the concentration of $I_2$ is 0.020 mol/L. What is the equilibrium concentration of HI?
Consider the equilibrium $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$. Initially, 0.100 mol of $H_2$ and 0.100 mol of $I_2$ are placed in a 1.00 L flask. At equilibrium, the concentration of $I_2$ is 0.020 mol/L. What is the equilibrium concentration of HI?
For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, if 0.200 mol of $N_2$ and 0.600 mol of $H_2$ are initially placed in a 1.00 L flask, and the equilibrium concentration of $NH_3$ is 0.00320 mol/L, what is the amount of $H_2$ remaining at equilibrium?
For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, if 0.200 mol of $N_2$ and 0.600 mol of $H_2$ are initially placed in a 1.00 L flask, and the equilibrium concentration of $NH_3$ is 0.00320 mol/L, what is the amount of $H_2$ remaining at equilibrium?
Le Châtelier's principle is best described by which of the following statements?
Le Châtelier's principle is best described by which of the following statements?
Flashcards
Dynamic Equilibrium
Dynamic Equilibrium
The point at which the rate of forward and reverse reactions are equal, resulting in no net change in reactant and product concentrations.
Equilibrium Constant (K)
Equilibrium Constant (K)
A value that tells us the relative amount of products and reactants present in a reaction at equilibrium.
Reaction Quotient (Q)
Reaction Quotient (Q)
The ratio of products to reactants at any given time; is used to determine whether a reaction is at equilibrium, or will proceed forward or backward.
Q < K
Q < K
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Q > K
Q > K
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Le Châtelier's Principle
Le Châtelier's Principle
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Magnitude of K
Magnitude of K
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Pure solids/liquids in K
Pure solids/liquids in K
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Study Notes
- CHEM 191 covers energetics and equilibria in biological systems.
- This is Module 1 Lecture 3, focusing on equilibrium.
- The learning objectives include the ability to write correct expressions for Q and K, understand the difference between Q and K, understand the information an equation K provides, and solve problems involving equilibrium.
Chemical Reactions and Equilibrium
- Chemical reactions do not always go to completion.
- A reaction quotient (Q) quantifies the amounts of reactants and products present in a reaction mixture over time.
- For the general reaction aA + bB ⇌ cC + dD, the reaction quotient expression: Q = ([C]^c[D]^d) / ([A]^a[B]^b).
- Concentration terms are raised to the power of the stoichiometric coefficients.
- Equilibrium is reached when the rate of forward and reverse reactions are equal.
- At equilibrium, the concentrations of reactants and products remain constant.
Dynamic Equilibrium
- At dynamic equilibrium, the reaction converting N2O4 into NO2 is still happening.
- As quickly as NO2 molecules are being formed, other NO2 molecules are being converted back into N2O4 molecules.
- Equilibrium can be quantified using the equilibrium constant K.
- At equilibrium, Q = K.
Equilibrium Constant
- For the general equilibrium aA(g) + bB(g) ⇌ cC(g) + dD(g), the equilibrium constant expression is K = ([C]^c[D]^d) / ([A]^a[B]^b).
- The subscript 'e' signifies concentrations at equilibrium.
- In general, when Q < K, the reaction needs to convert reactants into products to reach equilibrium.
- When Q > K, the reaction needs to convert products back into reactants until equilibrium is reached.
- K only depends on temperature, not on the starting concentrations.
- Products are raised to the power of stoichiometric coefficients while writing an equilibrium constant expression.
- Reactants are on the bottom of the equilibrium constant expression.
- Pure solids and pure liquids do not appear in the equilibrium constant expression because their concentrations are constant.
Magnitude of K
- The value of K gives information about the extent of the reaction at equilibrium.
- For equilibrium, K = ([H₂O]^2) / ([H2]^2[O2]) = 9.1×10^80 and the reaction goes essentially to completion.
- For equilibrium, K = ([NO]^2) / ([N2][O2]) = 4.8×10^-31 and the reaction barely begins when equilibrium is established.
Calculating K
- Equilibrium position lies to the left, remember that Kc has no units.
- Use the ICE table to reach equilibrium:
- Initial concentration
- Change in concentration, use the stoichiometry to find relationships
- Equilibrium concentration by adding initial + change in concentration (Equilm).
- To calculate K, use the final equilibrium concentrations. K = [NH3]^2 / [N2][H2]^3 = 2.46x10^-4
Response to Change
- Systems at equilibrium respond to changes in the amounts of reactants/products and pressure.
- Le Châtelier's principle states that "if a system at equilibrium is disturbed, it will move in such a way to counteract the disturbance and restore equilibrium."
- Comparing Q and K is useful to determine this response.
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