{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

ALS6A - Section 6 Chemical Equilibria Suggested solutions 1...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Section 6/ Chemical Equilibria / Suggested solutions / SKH Bishop Baker Secondary School A-Level Chemistry Section 6 Chemical Equilibria 81 IB Q.5 (b) (i) K p = P HI 2 ; K c = [HI] 2 P H2 x P I2 [H 2 ][I 2 ] [1] + [1] (ii) K c = (3.6) 2 = 29.5 [1] + [1] (4 - 1.8)(2 - 1.8) (1 mark for the correct substitution; 1 mark for the correct answer.) 82 IB Q.9 (a) (i) K p = P H2S P NH3 P x = partial pressure [1] P H2S = P NH3 = 0.54/2 [ ½ ] + [ ½ ] K p = (0.54/2) 2 = 0.0729 atm 2 ( ½ mark for numerical answer; ½ mark for unit.) [1] (ii) either P H2S = y + 0.335 [ ½ ] P NH3 = y [ ½ ] or P H2S x P NH3 = K p y(y + 0.335) = 0.0729 [1] y = 0.15 atm ( ½ mark for numerical answer; ½ mark for unit.) [1] 83 IA Q.1 (d) To BiOCl(s) add small amounts of conc. HCl with shaking to dissolve the solid. [1] Add large excess of water. [1] 83 IB Q.9 (b) (i) K p = P H2O P H2 P O2 ½ [ ½ ] (iii) At equilibrium, P H2O = 1.18 x 10 40 P H2 P O2 ½ [ ½ ] Since P H2O P H2 P O2 ½ the reaction goes almost to completion at equilibrium. [1] 84 IB Q.8 (a) (i) By decreasing the temperature, or increasing the pressure. (Also accept the increase of concentration of the reactants or the removal of product as soon as it is formed. Any one [1] Additional wrong answer : - 1 mark) (ii) High yield of Z is favoured by a low temperature. [1] However, the time for reaching the equilibrium at a low temperature will be too long , [1] (Rate of reaction is too slow.) so a compromise in temperature (723 K) is chosen [ ½ ] so that the percentage of product is not too low, while the time to reach equilibrium is not too long. High yield of Z is favoured by high pressure . [1] However, high pressure is economically expensive , [1] so a compromise is again chosen. [ ½ ] (iii) 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Section 6/ Chemical Equilibria / Suggested solutions / Effect : 1. Time to reach equilibrium is longer . [1] Reaction rate will be much slower. 2. Percentage of product is unaffected . [1] (iv) xX(g) + yY(g) == zZ(g) At equilibrium, k 1 [X] x [Y] y = k -1 [Z] z [1] K = [Z] z = k 1 [X] x [Y] y k - 1 [1] (No working - 1 mark) 85 IA Q.1 (c) K c = [CO 2 ] 2 /[CO] 2 or K p = P CO2 2 /P CO 2 [1 ½ ] [No indication of K c or K p 1 mark only] Give the corresponding concentration terms of CO and CO 2 (e.g. partial pressure ) at a given temperature. [1 ½ ] [Pressure only 1 mark; but should correspond to the equation.] 86 IIA Q.3 (a) (i) (CH 3 COOH) 2 == 2CH 3 COOH 1 - α 2 α α = degree of dissociation Partial pressure of (CH 3 COOH) 2 = [1 - α ]P / [1 + α ] [ ½ ] Partial pressure of CH 3 COOH = 2 α P / [1 + α ] [ ½ ] [2 α / (1 + α )] 2 P 2 K p = [1 - α ]P / [1 + α ] = 4 α 2 P / [1 - α 2 ] [1] At 298 K and 1500 N m - 2 , 72.9 = 4 α 2 /[1 - α 2 ] x 1500, α = 0.11 (0.109 0.111) [1] (ii) K p 72.9 121.1 182.7 302.0 log 10 K p 1.863 2.083 2.262 2.480 T 298 303 308 313 1/T x 10 3 3.36 3.30 3.25 3.19 (Table form : [1]) A plot of log 10 K p against 1/T gives a straight line. The equation is obeyed. [1] 2
Background image of page 2
Section 6/ Chemical Equilibria / Suggested solutions / (iii) Slope = - H = 2.480 - 1.950 x 10 3 [1] 2.303 x 8.314 3.190 - 3.335 H = 70.0 kJ mol -1 ( ± 2.0) [1] (iv) The heat of dissociation for one mole of ethanoic dimers is 70.0 kJ mol - 1 . Since the dissociation of one dimer involves the breaking of two hydrogen bonds.[1] the energy of hydrogen bond is 35.0 kJ mol - 1 . [1] 87 IA Q.1 (a) (i) Some B has been added. [1] [0. 015 mol dm - 3 of B has been added or concentration of B has been increased from 0.02 to 0.035 mol dm - 3 ……. 1 + ½ BONUS] (ii) K c = [AB]/[A] x [B] = 0.02/0.04 x 0.03 = 16.67 mol - 1 dm 3 [1] (accept 16.6 16.7 M - 1 .) (ii) K c = [AB]/ [A] x [B] = 0.01/0.05 x 0.04 = 5
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}