Chapter 13 Q's
Consider the following reaction: CH₃COOH(aq) + H₂O(l) ⇌ CH₃COO⁻(aq) + H₃O⁺(aq). An increase in the pressure of the chamber where this reaction takes place will result in
A change in pressure will only affect an equilibrium with gaseous species.
Which of the following changes would cause the reaction below to shift in the forward direction to reestablish equilibrium? 2 NBr₃ (g) ⇌ N₂ (g) + 3 Br₂ (g)
An increase in volume would result in a decrease in pressure. This would shift to the forward direction to produce more products.
Consider the following energy diagram and determine which of the following statements is true.
At equilibrium, we would expect the concentration of the products to get greater than the concentration of the reactants because the activation energy is lower for the forward reaction. In this case, kf/kr>1 meaning that Keq>1. This indicates that products are favored at equilibrium.
For the reaction: Mg(OH)₂ (s) ⇌ Mg²⁺ (aq) + 2 OH⁻ (aq) Adding Mg(OH)₂ will
Compounds which are solids and liquids have constant composition and therefore do not appear in the equilibrium expression. Adding more solid will have no effect.
Which of the following is the correct expression for the concentration based equilibrium constant for the reaction: Mg(OH)₂ (s) ⇌ Mg²⁺ (aq) + 2 OH⁻ (aq)
Compounds which are solids and liquids have constant composition and therefore do not appear in the equilibrium expression. Equilibrium constants are the products divided by the reactants. Coefficients become exponents. In this case, the equilibrium constant would be Kc=[Mg2+][OH−]2
Consider the following reaction: 2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g). If you decrease the volume of the reaction chamber, you would observe
Decreasing the volume increases the pressure, which will decrease the number of molecules on the side of the reaction with more gas.
Consider the equilibrium constant below. Which of the following reactions would fit this equilibrium constant?
Equilibrium constants are the products divided by the reactants. Coefficients become exponents. In this case, the equilibrium constant shows that the product is A and the reactants are B and C. It also shows the coefficient for C is 2. The balanced chemical reaction would be B+2C−⇀↽−AB+2C↽−−⇀A.
Which of the following is the correct expression for the pressure based equilibrium constant for the reaction: 4 NH₃ (g) + 7 O₂ (g) ⇌ 4 NO₂ (g) + 6 H₂O (g)
Equilibrium constants are the products divided by the reactants. Coefficients become exponents. In this case, the equilibrium constant would be represented as: Kp=(PNO2)4(PH2O)6/(PNH3)4(PO2)7
Which of the following is the correct expression for the concentration based equilibrium constant for the reaction: 2 C (aq) + D (aq) ⇌ 2 A (aq) + B (aq)
Equilibrium constants are the products divided by the reactants. Coefficients become exponents. In this case, the equilibrium constant would be represented as: Kc=[A]2[B]/[C]2[D].
If the reaction quotient (Q) for a given reaction is less than the equilibrium constant (K) then
If the reaction quotient (Q) for a given reaction is less than the equilibrium constant (K) then the reaction will proceed in the forward direction.
Consider the following acidic equilibrium: H₂CO₃(aq) + H₂O(l) ⇌ HCO₃⁻(aq) + H₃O⁺(aq). If you add NaHCO₃ to this solution, which of the following will occur?
If you add NaHCO₃ to this solution, the reaction will shift in the reverse direction to reestablish equilibrium.
For the reaction below, Q = 600. What must happen for the reaction to reach equilibrium? 2 A (g) + B (s) ⇌ 2 C (s) + D (g) Kp = 8210
Kp>Q and this indicates that the reaction will shift in the forward direction.
Reversible processes:
Reversible processes can only be approximated in real life because no process is 100% efficient and there are energy losses in the forward and reverse directions. If a process were truly reversible, then it would result in perpetual motion and be a violation of the 2nd Law of Thermodynamics.
Consider the following two reactions occurring in the same vessel: A ⇌ B, K=0.01 A ⇌ C, K=0.02 What will there be most of in solution?
The equilibrium constant is less than 1 for both reactions, meaning that there must be more reactants than products.
Consider the following diagrams which show the progress for the reaction A(blue) ⇌ B (red). The equilibrium constant (K) for this reaction is 0.8. At which point does the reaction reach equilibrium?
The equilibrium constant is the products divided by the reactants. A K value of 0.8 is consistent with image choice C where the ratio of product to react is 4:5
When NO₂ dimerizes (two molecules join together to form a 'dimer') into N₂O₄, an equilibrium is reached and in the process this reaction produces heat. If you increase the temperature of the chamber in which both NO₂ and N₂O₄ reside, you would observe
Think of the heat as a product in the equation. As the products are increased, the reaction will shift to the left to create more reactants to reach equilibrium.
Which of the following is true for a reaction at equilibrium?
When a reaction is at equilibrium there is no further change in the concentrations of the reactants and products. That means they must be formed at the same rate as they are breaking down, so the rate of the forward reaction is equal to the rate of the reverse reaction.