Kinetics & Equilibrium Review Packet Standard Level ANSWER KEY 1. A [1] 2. C [1] 3. B [1] 4. B [1] 5. B [1] 6. D [1] 7. C [1] 8. C [1] 9.

Transcription

1 Kinetics & Equilibrium Review Packet Standard Level ANSWER KEY 1. A. C 3. B 4. B 5. B 6. D 7. C 8. C 9. C 10. C 1

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3 11. D 1. C 13. D 14. C 15. A 16. A 17. C 18. D 19. C 0. C 3

4 1. (a) A; E; If 3 choices shown [1 max], if 4 choices shown [0]. (b) (i) after 15s (product) = 0.37 (mol dm 3 ); rate = 0.37 = 0.05; 15 sig figs mol dm 3 s 1 /Ms 1 / M ; 3 sec at equilibrium/rates of forward and reverse reactions are equal/ G = 0; 1 [6]. (a) 00 C 600 atm. (both for, units not needed); 1 allow the highest pressure and the lowest temperature (b) (i) yield increases/equilibrium moves to the right/more ammonia; 4 (gas) molecules /decrease in volume/fewer molecules on right hand side; yield decreases/equilibrium moves to the left/less ammonia; exothermic reaction/owtte; (c) high pressure expensive/greater cost of operating at high pressure/reinforced pipes etc. needed; lower temperature greater yield, but lowers rate; Do not award a mark just for the word compromise. (d) K c = [N [NH 3 ][H ] ] 3 (ignore units); 1 [8] 4

5 3. (a) forward Rate reverse Time two curves one labelled forward starting up high up y-axis and one labelled reverse starting from zero; curves merge and become horizontal; No penalty for failing to label axes. forward reaction: highest concentration, thus rate high to begin with; as reaction proceeds, concentrations decrease, so does rate; reverse reaction: zero rate initially/at t = 0 (since no products present); rate increases as concentration of products increases; equilibrium established when rate of forward reaction = rate of reverse reaction; 7 (b) (reaction is) endothermic; Kc increases with (increasing) temperature; forward reaction favoured/heat used up/owtte; 3 [10] 4. (a) (position of) equilibrium shifts to the left/towards reactants; (forward) reaction is exothermic/ H is negative/the reverse reaction is endothermic/owtte; Do not accept Le Chatelier s Principle without some additional explanation. (b) (position of) equilibrium shifts to the right/towards products; fewer gas molecules on the right hand side/volume decreases in forward reaction/owtte; Do not accept Le Chatelier s Principle without some additional explanation. [4] 5

6 [NO ] 5. (i) ( K c = ) ; [N O ] 4 (horizontal line) concentration of reactant and product remains constant/equilibrium reached; (magnitude of) K c greater than 1; Accept 1.6. (iii) (iv) product concentration greater than reactant concentration; 4 increased temperature shifts equilibrium position to right; (forward) reaction is endothermic/absorbs heat; increased pressure shifts equilibrium to left; fewer (gas) moles/molecules on left; both/forward and reverse rates increased/increase in forward reverse rates are equal; activation energy reduced; position of equilibrium unchanged; concentration/amount of reactants and products remain constant; value of K c unchanged; K c only affected by changes in temperature; 6 [14] 6. (i) Number of molecules / frequency T 1 T both axes correctly labelled; E a Energy T peak/lower; and to right of T 1 ; 3 Area under graph is not important. 6

7 rate increased/changes; as more molecules with E a ; No explicit reference to graph required. [5] 7. (i) CaCO 3 (s) + H + (aq) Ca + (aq) + H O(l) + CO (g) 1 States not required, accept molecular equation. rate decreases with time; as concentration decreases so fewer (successful) collisions; draw tangent to the curve at time t; rate = slope or gradient; 4 (iii) Volume of CO produced original II I Time I. (less CO because) amount of HCl is limiting and half the orginal/owtte; II. (same amount of CO because) amount of HCl is the same; curve less steep because less frequent (accept fewer) collisions 5 Awarded last mark if in either I or II. [10] 8. (a) (i) it is decreasing; less frequent collisions/fewer collisions per second or (unit) time; reactant(s) used up/reaction is complete; 1 Do not accept reaction reaches equilibrium. 7

8 (b) (i) it would increase; 1 Accept a quantitative answer such as doubles. (iii) more frequent collisions; collisions or molecules have more energy (OWTTE); more molecules with energy E a ; 3 rate would be lower; smaller surface area; [9] 9. (a) measure volume of carbon dioxide/co /gas produced/measure ph; 4 starts at origin and levels off measure mass of chemicals/apparatus; starts high and decreases Graph should show increase as reaction progresses (as HCl is consumed). 8

9 (b) Method 1 use powdered MgCO 3 /OWTTE; particles collide more frequently/increased surface area/owtte; Method increase (reaction) temperature/heat/warm; more of the collisions are successful/more particles with E > E a /OWTTE; Method 3 increase acid concentration; more frequent (reactant) collisions; Method 4 add catalyst; lowers activation energy/e a /OWTTE; Award [] each for any three methods 6 max (c) (i) stays the same; MgCO 3 was already in excess; stays the same; same quantities of reactants used; [14] 30. (i) reversible reaction/reaction may proceed in either direction (depending on reaction conditions) equilibrium/dynamic equilibrium; 1 (iii) no effect; catalyst will speed up both forward and reverse reactions (equally)/ increase the rate at which equilibrium is achieved; acidity: no effect; equilibrium shifts to the right; K c : no change; 3 [6] 9