Ch 15 Chemical Equilibrium STUDY GUIDE Accelerated Chemistry SCANTRON. Name /98

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1 Ch 15 Chemical Equilibrium STUDY GUIDE Accelerated Chemistry SCANTRON Name /98 TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. Correct the False statments by changing the underlined word(s). 1) Equilibrium involves the ideas of sameness and constancy. 1) 2) Living things are in equilibrium with their surroundings. 2) 3) The rate of a chemical reaction is the amount of reactant that changes to product in a specific amount of time. 3) 4) Collisions between reactant molecules do not always lead to the formation of product molecules. 4) 5) Reaction rates generally increase as a reaction proceeds. 5) 6) The rate of a reaction increases with increasing concentrations of reactants because you have more collisions occurring in a given time period. 6) 7) The rate of a chemical reaction is inversely proportional to the temperature. 7) 8) A reversible reaction is one that can be stopped and then restarted as needed. 8) 9) Dynamic equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction. 9) 10) Dynamic equilibrium is established when the rate of the forward reaction goes to zero. 10) 11) When dynamic equilibrium is achieved, the concentrations of reactants is equal to the concentrations of the products. 11) 12) When dynamic equilibrium is achieved, the rate of the forward and backward reactions go to zero. 12) 13) The Equilibrium Constant, K eq, is a way to quantify the relative concentrations of the reactants and products of a reaction at equilibrium. 13) 14) It is not necessary to have a balanced equation before writing an equilibrium constant expression. 14) 15) The larger the equilibrium constant, the greater is the concentration of reactants relative to products at equilibrium. 15) 16) As long as K eq > 1, all reactants will eventually be consumed and leave us exclusively with product molecules. 16) 1

2 17) Placing a [ ] around the formula of a chemical means that we are referring to the molar concentration of that chemical. 17) 18) A reaction that has K eq = will have high concentrations of products. 18) 19) A reaction that has K eq = will have high concentrations of products. 19) 20) For a given chemical equation, the coefficients for each substance become the exponents for each substance in the written equilibrium expression. 20) 21) If K eq = 2 for the reaction X Y, then the K eq for Y X will be 1/2 (or 0.5). 21) 22) The equilibrium expression for the reaction: 2C(s) + 2H 2 O(l) CH 4 (g) + CO 2 (g) is K eq = [CH 4 ][CO 2 ]. 22) 23) The equilibrium constant, K eq, for an equilibrium reaction will always be the same (at a given temperature) regardless of what the initial concentrations of reactants and products were. 23) 24) Le Chatelier's principle states that a chemical system must have a shift in direction in order to force the system to reach equilibrium. 24) 25) Le Chatelier's principle states that when a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance. 25) 26) Increasing the amount of carbon in the reaction below will cause the reaction to proceed to the left so that equilibrium will be restored. 26) 2C(s) + 2H 2 O(l) CH 4 (g) + CO 2 (g) 27) Decreasing the amount of carbon dioxide in the reaction below will cause the reaction to proceed to the right so that equilibrium will be restored. 27) 2C(s) + 2H 2 O(l) CH 4 (g) + CO 2 (g) 28) If you have a chamber of gases at equilibrium, compressing the gases to half the original volume would have the same effect as doubling the pressure. 28) 29) Decreasing the volume of the system below causes the reaction to shift towards the right. 29) C(s) + 2H 2 (g) CH 4 (g) 30) Increasing the volume of the system below causes the reaction to shift towards the right. 30) C(s) + 2H 2 (g) CH 4 (g) 31) In an exothermic reaction, you can consider the emitted heat as a reactant in this system. 31) 2

3 32) Adding heat to an endothermic reaction causes the reaction to shift to the right. 32) 33) Adding heat to an exothermic reaction will cause the reaction to remain unchanged. 33) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 34) A description of life is: 34) A) Living things maintain and control their equilibrium. B) Living things maintain and control their disequilibrium. C) Living things maintain and control their changelessness. D) Living things maintain and control their sameness. 35) According to the collision theory of chemical reactions: 35) A) low energy collisions do not occur in the gas phase. B) low energy collisions result in many successful reactions as there is sufficient time for the reactants to form products. C) high energy collisions result in few successful reactions as there isn't sufficient time for the products to react. D) high energy collisions lead to the successful formation of products. 36) Which of the following changes will increase the reaction rate? 36) A) a decrease of the reaction temperature B) an increase in the concentration of reactants C) allowing more time for the reaction D) an increase in the concentration of the products 37) Which of the following changes will increase reaction rate? 1. An increase in the concentration of reactants 2. An increase in temperature 3. Higher-energy collisions between reacting molecules A) 1 and 2 only B) 2 and 3 only C) 1 and 3 only D) All of 1, 2, and 3 37) 38) Why does the rate of the reaction decrease over time? 38) A) As the reaction proceeds, a decrease in the concentration of reactants results in fewer successful collisions. B) Not all molecules will react and some choose to stay in their present form. C) As the reaction proceeds, the concentration of the products results in fewer collisions. D) Exothermic reactions lose heat which cools the reaction which decreases reaction rate. 39) Which of the following is TRUE for a system that is in dynamic equilibrium? 39) A) Both the forward and reverse reactions come to a halt. B) The concentration of products is equal to the concentration of the reactants. C) The reaction rate of the forward reaction approaches zero. D) none of the above 3

4 40) Which of the following is TRUE about a chemical system in equilibrium? 40) A) Reaction rate remains stable as long as temperature and pressure are stable. B) Addition of more reactants have no effect on reaction rate. C) Temperature changes have no effect on reaction rate. D) No reaction takes place. 41) Suppose a wall divides a playground, and twenty balls lie on the ground on the east side, while forty balls lie on the west side. If a child on the east side of the wall always tosses a ball over the wall at the same time a child on the west side tosses a ball over the wall, then A) all balls will eventually end up on one side. B) this system can never reach equilibrium. C) equilibrium will be established once thirty balls are on each side. D) equilibrium has been established. 41) 42) A chemical equilibrium exists when 42) A) there are equal amounts of reactants and products. B) the sum of reactant and product concentrations equals one mole. C) the rate at which reactants form products is the same as the rate at which products form reactants. D) reactants are completely changed to products. 43) A system is said to be in dynamic equilibrium when: 43) A) there is no longer any net change in the concentrations of products or reactants. B) the forward and reverse reactions come to a halt. C) you have let the reaction proceed for approximately 30 minutes and can assume there will be no more changes. D) the sum of the concentrations of the reactants is equal to the sum of the concentrations of the products. 44) Given N2 (g) + 3 H2 (g) 2 NH3 (g), which scenario will allow you to eventually reach an equilibrium mixture involving these chemicals? A) Place only H2 into a sealed vessel. B) Place only N2 into a sealed vessel. C) Place only NH3 into a sealed vessel. D) All of the above scenarios. 44) 45) For the reaction aa + bb cc + dd, the equilibrium expression is: 45) A) K eq = [A] a[b]b B) K eq = [C][D] C) K eq = [C] c[d]d D) K eq = [A][B] [C]c[D]d [A][B] [A]a[B]b [C][D] 46) For the reaction 2A + B 2C + 3D, the equilibrium expression is: 46) A) K eq = [A] 2[B] B) K eq = [2C][3D] C) K eq = [2][1] D) K eq = [C] 2[D]3 [C]2[D]3 [2A][B] [2][3] [A]2[B] 47) The chemical equation that would generate the equilibrium expression Keq = [B] 2 [C] [A]3. (Assume all substances are gases in this reaction.) A) 3A 2B + C B) A B + C C) C + 2B 3A D) 1/2 B + C 1/3 A is 47) 4

5 48) For the reaction S2F6 2SF2 + F2, the equilibrium expression is: 48) A) K eq = [SF 2][F2] [S2F6] B) K eq = [SF 2]2[F2] [S2F6] C) K eq = [S2F6] [SF2]2[F2] D) K eq = [S 2F6] [SF2][F2] 49) Which equilibrium constant represents a reaction that favors the formation of the products to the greatest extent? A) K eq = B) K eq = C) K eq = D) K eq = ) 50) Which equilibrium constant represents a reaction that favors the reactants to the greatest extent? A) K eq = B) K eq = 100 C) K eq = D) K eq = ) 51) Which of the following is TRUE of a system for which K eq << 1? 51) A) It will take a short time to reach equilibrium. B) It will take a long time to reach equilibrium. C) The equilibrium favors the reverse reaction. D) The equilibrium favors the forward reaction. 52) Which of the following is TRUE of a system for which K eq >> 1? 52) A) It will take a long time to reach equilibrium. B) It will take a short time to reach equilibrium. C) The equilibrium favors the reverse reaction. D) The equilibrium favors the forward reaction. 53) Identify the equation for which K eq = [Cu+]2[ S2-]. 53) A) 1 2 Cu 2S(s) Cu + (aq) S 2- (aq) B) Cu 2S(s) Cu + (aq) + 2S2- (aq) C) CuS(s) Cu2+ (aq) + S 2- (aq) D) Cu 2S(s) 2Cu + (aq) + S2- (aq) 54) What must be TRUE for a reaction possessing a large equilibrium constant? 54) A) The reaction rate is slow. B) The forward reaction is favored. C) The reaction rate is fast. D) The reverse reaction is favored. 55) When writing the expression for an equilibrium constant, which type of substance IS included? A) pure liquids B) gases C) solids D) all of the above 55) 5

6 56) For the reaction 2 H2O (l) 2H2 (g) + O2 (g), the equilibrium expression is: 56) A) K eq = [H 2]2 [O]2 B) K eq = [H2O]2 [H2O]2 C) K eq = [H 2]2 [O2] [H2O]2 D) K eq = [H2]2 [O2] 57) For the reaction Cu 2 S(s) 2Cu+(aq) + S2-(aq), the equilibrium expression is: 57) A) K eq = [Cu+]2[ S2-] B) K eq = [Cu2S] C) K eq = [Cu +]2[ S2-] [Cu2S] D) K eq = [Cu +][ S2-] [Cu2S] 58) For the reaction 2 A B, the equilibrium concentrations are as follows: [A] = M and [B] = 0.12 M. Calculate the equilibrium constant (K eq ) for the reaction. A) 0.26 B) 2.1 C) 38 D) ) 59) For the reaction S2F6(g) 2SF2(g) + F2(g), [SF2] = 0.18 M, [F2] = 0.54 M.The quilibrium constant is: A) 0.44 B) 2.3 C) 6.7 D) ) 60) For the reaction S2F6(g) 2SF2(g) + F2(g), the equilibrium concentrations are as follows: [S2F6] = M, [SF2] = 2.08 M, [F2] = 1.32 M. The equilibrium constant is: A) B) C) D) ) 61) For the reaction Cu 2 S(s) 2Cu+(aq) + S2-(aq), the equilibrium concentrations are as follows: [Cu+] = M, [ S2-] = M. The equilibrium constant is: A) B) C) D) ) 62) For the reaction LiOH (s) Li+ (aq) + OH- (aq), K eq = , and the equilibrium concentration for hydroxide ion is [OH-] = M. What is [Li+] at equilibrium? A) 0.11 M B) M C) M D) none of the above 62) 63) For the reaction Ag 2 S(s) 2Ag+(aq) + S2-(aq), K eq = and the equilibrium concentration of silver ion is [Ag + ] = M. What is [ S 2- ] at equilibrium? A) B) C) D) ) 64) For the reaction Ag2S(s) 2Ag + (aq) + S2- (aq), Keq = , and the equilibrium concentration of sulfide ion is [ S 2- ] = M. What is [Ag + ] at equilibrium? A) M B) 0.32 M C) 0.10 M D) M 64) 6

7 65) Le Chatelier's Principle states that: 65) A) when a system at equilibrium is disturbed, a new equilibrium constant is established. B) when a chemical system is at equilibrium it is no longer possible to alter the system. C) a disturbing force must be applied to a system in order for it to reach equilibrium. D) when a chemical system at equilibrium is disturbed, the system shifts in order to minimize the effect. 66) For the reaction Ag 2 S(s) 2Ag + (aq) + S2- (aq), what happens to the equilibrium position if aqueous ammonium sulfide is added? A) shifts to the right B) does nothing C) doubles D) shifts to the left 66) 67) For the reaction Ag 2 S(s) 2Ag + (aq) + S2- (aq), what happens to the equilibrium position if ammonium sulfate is added? A) shifts to the left B) does nothing C) shifts to the right D) halves 67) 68) For the reaction Ag 2 S(s) 2Ag + (aq) + S2- (aq), what happens to the equilibrium position if the amount of solid silver sulfide is doubled? A) halves B) shifts to the left C) does nothing D) doubles 68) 69) For the reaction Ag 2 S(s) 2Ag + (aq) + S2- (aq), what happens to the equilibrium position if the amount of silver ion is halved? A) shifts to the left B) shifts to the right C) does nothing D) halves 69) 70) Consider the reaction: 2N2O(g) O2(g) + 2N2(g). Which of the following will cause a shift in the equilibrium to the right? 1. Add more N 2 O 2. Remove O2 3. Remove N 2 A) 1 and 3 only B) 2 and 3 only C) 1 and 2 only D) All of 1, 2, and 3 70) 71) Consider the reaction: 2N2O(g) O2(g) + 2N2(g). Which of the following will cause a shift in the equilibrium to the left? 1. Remove N 2 O 2. Remove O 2 3. Add N2 A) 1 and 3 only B) 2 and 3 only C) 1 and 2 only D) All of 1, 2, and 3 71) 7

8 72) We have the following reaction at equilibrium in a flask, CaSO 4 (s) Ca2+(aq) + SO 4 2+(aq) What will happen to [Ca2+] if additional CaSO 4 is added to the flask? A) It will increase. B) It will not change. C) It will decrease. D) Cannot tell with the information provided. 72) 73) For the reaction 2N2O(g) O2(g) + 2N2(g), what happens to the equilibrium position if the pressure increases? A) shifts to the right B) halves C) shifts to the left D) doubles 73) 74) For the reaction H2 (g) + Cl2 (g) 2 HCl (g), what happens to the equilibrium position if the pressure increases? A) shifts to the left B) does nothing C) shifts to the right D) doubles 74) 75) For the reaction 2N2O(g) O2(g) + 2N2(g), what happens to the equilibrium position if the pressure decreases? A) doubles B) shifts to the left C) halves D) shifts to the right 75) 76) For the reaction 2N2O(g) O2(g) + 2N2(g), what happens to the equilibrium position if the volume decreases? A) shifts to the right B) does nothing C) shifts to the left D) doubles 76) 77) For the reaction 2N2O(g) O2(g) + 2N2(g), what happens to the equilibrium position if the volume increases? A) halves B) shifts to the right C) shifts to the left D) doubles 77) 78) What happens to the equilibrium position of an exothermic reaction when you add heat? 78) A) halves B) shifts to the right C) shifts to the left D) does nothing 79) What happens to the equilibrium position of an exothermic reaction when you remove heat? 79) A) doubles B) shifts to the right C) shifts to the left D) does nothing 80) What happens to the equilibrium position of an endothermic reaction when you add heat? 80) A) doubles B) shifts to the right C) shifts to the left D) halves 8

9 81) What happens to the equilibrium position of an endothermic reaction when you remove heat? 81) A) shifts to the left B) shifts to the right C) doubles D) halves 82) Which compound is the most soluble? 82) A) AgCl, K sp = B) CuS, K sp = C) PbS, K sp = D) AgI, K sp = ) Which compound is the least soluble? 83) A) AgI, K sp = B) PbS, K sp = C) CuS, K sp = D) AgCl, K sp = ) What is the K sp expression for the ionic compound Li2CO3? 84) A) K sp = [Li+]2 [CO3 2- ] B) K sp = [Li2CO3]3 C) K sp = 2[Li+] [CO3 2- ] D) K sp = [Li+] [CO3 2- ] 85) What is the [Cu2+] at equilibrium, given CuS, K sp = ? 85) A) M B) M C) M D) M 86) What is the [Ag+] at equilibrium, given AgCl, K sp = ? 86) A) M B) M C) M D) M 87) What is the molar solubility, (S), of FeS if the K sp = for this substance? 87) A) M B) M C) M D) M 88) Which statement about activation energy is FALSE? 88) A) The lower the activation energy, the faster the reaction rate. B) Activation energy is an energy hump that normally exists between reactants and products. C) The higher the activation energy, the slower the reaction rate. D) Increasing the temperature lowers the activation energy. 89) The effect of a catalyst is to: 89) A) increase the number of collision between reactants. B) change the stoichiometry of the reaction. C) lower the activation energy of a reaction whereby making it easier for the reactants to get over the energy hump. D) increase the temperature of the reactants whereby more products are formed. 90) Comparing a reaction with a catalyst to the same reaction without the catalyst, each of the following statements is true EXCEPT A) The rate for the reaction with a catalyst is faster. B) The products are the same. C) The catalyzed reaction follows a different pathway. D) The activation energy is the same for both the catalyzed and uncatalyzed reaction. 90) 9

10 91) Which statement below is FALSE? 91) A) The rate of a reaction can be increased by adding a catalyst. B) The rate of a reaction can be increased by altering the temperature. C) The rate of a reaction can be increased by increasing concentrations of reactants. D) A catalyst alters the equilibrium constant. 92) What happens to the equilibrium constant when a catalyst is added to the reaction mixture? 92) A) decreases B) varies C) does not change D) increases 93) Which of the following is FALSE about enzymes? 93) A) They act as biological catalysts. B) They increase the temperature of biological reactions to speed them up. C) They are highly specific in their catalytic activity. D) They lower the activation energy of biological reactions. 94) Calculate the equilibrium constant for the reaction below given that [Cl2] = 0.11 M, [H2] = 0.15 M, and [HCl] = 0.95 M at equilibrium. Given: Cl2(g) + H2(g) 2HCl(g) A) B) 58 C) D) 55 94) 95) Calculate the concentration of NO2 in an equilibrium mixture given that the concentration of N2O4 = M and K eq = 45.5 for the reaction: 2NO2(g) N2O4(g). A) M B) M C) 15.1 M D) M 95) 96) Calculate [M + ] at equilibrium given that the Ksp = for the reaction MX(s) M + + X -. A) 0.19 M B) M C) 0.0 M D) not enough information given 96) 97) What is the concentration of the Mg2+ ion in solution when [CO3 2- ] = 0.25 M given that the Ksp = for the following reaction: MgCO3 (s) Mg2+(aq) + CO3 2- (aq)? A) 19.2 B) C) D) ) 98) What is the value for the Ksp for a compound MX(s) if at equilibrium [M + ] = M? 98) A) B) C) D) not enough information 10