DAT General Chemistry - Problem Drill 14: Chemical Equilibrium

Transcription

1 DAT General Chemistry - Problem Drill 14: Chemical Equilibrium Question No. 1 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 1. What is the equilibrium constant for N O 4 (g) NO (g) if the equilibrium concentrations are: [N O 4 = M and [NO = M? Question #01 (A) (B) 3.00 (C) (D) (E) A. Incorrect Remember that when writing equilibrium constant expressions, the products are over the reactants with the balanced equation coefficients as the exponents. B. Incorrect Remember that when writing equilibrium constant expressions, the products are over the reactants with the balanced equation coefficients as the exponents. C. Incorrect Remember that when writing equilibrium constant expressions, the products are over the reactants with the balanced equation coefficients as the exponents. D. Incorrect Remember that when writing equilibrium constant expressions, the products are over the reactants with the balanced equation coefficients as the exponents. E. Correct. You correctly calculated the equilibrium constant. N O 4 (g) NO (g) [N O 4 eq = M [NO eq = M? [ NO [ N O 4 ( )

2 Question No. of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question : The reaction quotient for a system is If the equilibrium constant is 6, which way will the reaction proceed to reach equilibrium? Question #0 (A) To the right (B) To the left (C) It is at equilibrium (D) Not enough information (E) None of the above A. Incorrect. If the reaction quotient is too big, the top of the fraction (the products) needs to decrease. B. Correct. If the reaction quotient is too big, the top of the fraction (the products) needs to decrease. C. Incorrect. If the reaction quotient is too big, the top of the fraction (the products) needs to decrease. D. Incorrect. If the reaction quotient is too big, the top of the fraction (the products) needs to decrease. E. Incorrect. If the reaction quotient is too big, the top of the fraction (the products) needs to decrease. Q = Which way will reaction go? If Q = K, it s at equilibrium If Q > K, there are too many products and too few reactants If Q < K, there are too few products and too many reactants Q > K. There are too many products. The reaction will shift to the left to reduce the products and make more reactants.

3 Question No. 3 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 3: What is the correct equilibrium constant expression for the following reaction? NO Cl (g) NO (g) + Cl (g) Question #03 [ NO [ Cl [ NO Cl (A) (B) [ NOCl (C) [ NO [ Cl [ NO [ Cl (D) [ NOCl (E) [ NO [ Cl [ NOCl [ NO [ Cl A: Incorrect. B: Incorrect. C: Incorrect. D: Correct. E. Incorrect Molecules are only left out of equilibrium constants if they are pure solids or liquids. [ NO [ Cl [ NO Cl Mental Short Cut 1) since there is only one reactant and two products, focus on the reactants, ) recognize that the reactants will always be in the denominator, 3) stochiometry dictates that the denominator will be squared. 4) look for an answer with a square in the denominator, then confirm that it is the correct chemical species. 5) move on to the next question.

4 Question No. 4 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 4: Which of the changes will shift the reaction to the right when disturbing equilibrium for N (g) + 3 H (g) NH 3 (g) kj? Question #04 I. Increasing temperature II. Decreasing temperature III. Increasing volume IV. Decreasing volume V. Removing NH 3 VI. Adding NH 3 VII. Removing N VIII. Adding N (A) I, IV, VI, VII (B) II, III, V, VIII (C) I, VI, VIII (D) II, IV, V, VIII (E) I, III, V, VIII A: Incorrect. Removing N is removing a reactant that would push the reaction to the left. B: Incorrect. Increasing volume lowers the pressure. The reaction will shift to the side with the greatest number of gas molecules to increase the pressure again. For this reaction, it would shift to the left. C: Incorrect. Increasing temperature for this reaction is an increase in a product that would push the reaction to the left. D: Correct. You chose all the options that would push the reaction to the right! E. Incorrect! Removing N is removing a reactant that would push the reaction to the left. I. Energy is a product. Increasing a product would push the reaction to the left. II. Energy is a product. Decreasing a product would push the reaction to the right III. Increasing volume pushes towards side with more moles of gas. The left has 4, the right has. It would push reaction towards left. IV. Decreasing volume pushes towards side with least moles of gas. It would push the reaction towards the right. V. Removing a product shifts the reaction towards the right VI. Adding a product shifts the reaction to the left VII. Removing a reactant shifts the reaction to the left VIII. Adding a reactant shifts the reaction to the right II, IV, V, VIII

5 Question No. 5 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 5: For NOCl (g) NO (g) + Cl (g) with , if 1.0 M NOCl and 1.0 M Cl are added to a vessel, what are the equilibrium concentrations for each species? Question #05 (A) [NOCl = 1.0 M; [NO = 1.0 M; [Cl = 1.0 M (B) [NOCl = 1.0 M; [NO = M; [Cl = 1.0 M (C) [NOCl = 1.0 M; [NO = M; [Cl = 1.0 M (D) [NOCl = 1.0 M; [NO = M; [Cl = 1.0 M (E) [NOCl = 1.0 M; [NO = M; [Cl = 1.0 M A. Incorrect. Equilibrium does not necessarily mean that all concentrations are equal. B. Correct. You solved for equilibrium concentrations correctly! C. Incorrect. Use an ICE chart to solve for equilibrium concentrations. D. Incorrect. Use an ICE chart to solve for equilibrium concentrations. E. Incorrect. Use an ICE chart to solve for equilibrium concentrations. NOCl (g) NO (g) + Cl (g) [NOCl initial = 1.0 M [Cl initial = 1.0 M [NO initial = 0 M Equilibrium concentrations of all 3 species Understanding the approximations used to solve this problem is VERY important. You will see them again. Believe it or not, the approximations make this problem easier to solve, not harder. They are worth learning. [ NO [ Cl [ NOCl [NOCl [NO [Cl Initial 1.0 M 0 M 1.0 M Change -x +x +x Equilibrium 1.0 x 0 + x 1.0 +x Since K is very tiny, approximations can be made for equilibrium concentrations Equilibrium 1.0 x ( ) [x [1.0 = [1.0 ( 1.0) ( 4) (1.0) = x x = [NOCl = = 1.0 M [NO = = M [Cl = = 1.0 M

6 Question No. 6 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) For the solubility equilibrium Ca(OH) (s) Ca + (aq) + OH -1 (aq), the addition of NaOH to the system will cause Question #06 (A) [OH - to increase as the mass of Ca(OH) in the system increases (B) [OH - to increase as the mass of Ca(OH) in the system remains the same (C) [OH - to decrease as the mass of Ca(OH) in the system increases (D) [OH - to decrease as the mass of Ca(OH) in the system decreases (E) [OH - to decrease as the mass of Ca(OH) in the system remains the same A. Correct. Adding a product will cause the reaction to shift to the left. B. Incorrect. Adding a product will cause the reaction to shift to the left. B. Incorrect. Adding a soluble hydroxide compound causes the hydroxide concentration to increase. D. Incorrect. Adding a product will cause the reaction to shift to the left. E. Incorrect. Adding a product will cause the reaction to shift to the left. Adding a product will cause the reaction to shift to the left. Adding a soluble hydroxide compound causes the hydroxide concentration to increase.

7 Question No. 7 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 7: H + I HI Write the equilibrium constant expression for this all gas reaction? Question #07 (A) (B) (C) (D) (E) [ H [ I [ HI [ H [ I [ HI [ HI [ H [ I [ HI [ H [ I [ HI [ H[ I A: Incorrect. B: Incorrect. C: Correct. D: Incorrect. E. Incorrect! Ratio of products over reactants using balanced equation coefficients as powers [ HI [ H [ I

8 Question No. 8 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 8: If the equilibrium constant K for the reaction A B + C is 5, what is the equilibrium constant for the reverse reaction at the same temperature? Question #08 (A) 6 (B) 5 (C) 1/5 (D) 1/6 (E) Cannot be determined A: Incorrect. When you flip a reaction, take the inverse of the equilibrium constant. B: Incorrect. When you flip a reaction, take the inverse of the equilibrium constant. C: Correct. When you flip a reaction, take the inverse of the equilibrium constant. D: Incorrect. When you flip a reaction, take the inverse of the equilibrium constant. E. Incorrect! When you flip a reaction, take the inverse of the equilibrium constant. When reversing the reaction, take the inverse of the equilibrium constant.

9 Question No. 9 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 9. For the following gas reaction H + I HI What would be in the E row of the ICE chart below? Question #09 H I HI Initial 0.5 M 0.5 M 0 M Change Equilibrium (A) 0.5 M, 0.5 M, 0.5 M (B) x, -x, +x (C) 0.5 x, 0.5 x, x (D) +x, +x, -x (E) x, x, -x A. Incorrect. The reaction will shift to the right and have different final concentrations than the original concentrations because the product is initially 0 M. B. Incorrect. That is the C row of the ICE chart. C. Correct. You ve correctly determined the E row in the ICE chart. D. Incorrect. That information is similar to what would be in the C row except that the signs are opposite reactants will decrease and products will increase. E. Incorrect. The signs would be opposite as reactants would decrease and products would increase. H I HI Initial 0.5 M 0.5 M 0 M Change -x -x +x Equilibrium 0.5 M -x 0.5 -x x

10 Question No. 10 of 10 Instruction: (1) Read the problem statement and answer choices carefully () Work the problems on paper as needed (3) Question 10. Adding H to this gas system at equilibrium H + I HI Would cause which? Question #10 (A) Reaction would shift to the right (B) Reaction would shift to the left (C) Reaction would go both ways (D) No change (E) Cannot be determined A. Correct. B. Incorrect. C. Incorrect. D. Incorrect. E. Incorrect.