What temperature-pressure combination would maximize the concentration C_5H_6? T

Question

What temperature-pressure combination would maximize the concentration C_5H_6? Temperature Pressure (A)High High iB)High Low (C)Low High (D)Low low 28. At constant temperature and pressure, which will give the largest equilibrium constant? (A)negative DeltaH and positive DeltaS (B)negative DeltaH and negative DeltaS (C)positive DeltaH and positive DeltaS (D)positive DeltaH and negative DeltaS 29.What is the equilibrium constant for reaction 3? 1. AgCI(s) Ag^+(aq) + CI^- (aq) K_IP = 1.8 times 10^-10 2. Ag^+(aq) + 2NH,(aq) [Ag(NH_3]^+(aq) K = 1.5 times 10^7 3. AgCI(s) + 2NH_39aq) [Ag(NH_3)]^+9aq) + CI^-(aq) (A) 1.5 tiems 10^7 (B) 3.7 times 10^2 (C) 2.7 times 10^-3 (D) 1.8 times 10^-10 30.Which gas phase equilibrium is least affected by changing the volume of its container? (A)2NO_2 N_2O_4 (B)S_3O_9 3SO_3 (C)CIF, CIF_3 + CI_2 (D)2BrCI Br_2 + CI_2 31. Which aqueous solution is a buffer system? (A) HCl.NaCI (B) KOH.KNO_3 (C) H_2SO_4, CH_3COOH (D) CH_3COOH. CH_3COONa 32. Ten milliliters of 0.10 M ammonium chloride is titrated with 0.10 M sodium hydroxide. The titration curve is shown What is the approximate pK_a of the ammonium ion? (a) 7.2 (B) 9.0 (C) 10.5 (D) 12.0

Explanation / Answer

27. A system that releases heat to the surroundings, an exothermic reaction, has a negative H by convention, because the enthalpy of the products is lower than the enthalpy of the reactants of the system and A system of reactants that absorbs heat from the surroundings in an endothermic reaction has a positive H, because the enthalpy of the products is higher than the enthalpy of the reactants of the system. Since here in this case given enthalpy of reaction is positive reaction is endothermic. Therefore if we add heat from outside equilibrium will be shifted to right and we will get more yield of product. Also here one molecule is splitting to make 2 moles of C5H6 so pressure of system is increasing and hence if we keep the pressure of system low it will favours the product formation. Hence option B is correct, high Temperature and low pressure.

28. At constant pressure and temperature when Enthalpy of the reaction will be less than 0 and entropy would be greater than 0 we will get largest value for equilibrium constant. Hence here option A is correct.

29. AgCl + 2NH3 à Ag(NH3)2 + Cl-

K for your reaction = (Cl-)[Ag(NH3)2+]/(NH3)2 (AgCl)(s)

Equilibrium constant for 3rd reaction can be calculated as Ksp*K.

Keq= 1.8 × 10-10 ×1.5 × 107 = 2.7 × 10-3

31. A buffer is a solution that can resist pH change upon the addition of an acidic or basic components. It is able to neutralize small amounts of added acid or base, thus maintaining the pH of the solution relatively stable. To effectively maintain a pH range, a buffer must consist of a weak conjugate acid-base pair, meaning either a. a weak acid and its conjugate base, or b. a weak base and its conjugate acid. For example; acetic acid (weak organic acid w/ formula CH3COOH) and a salt containing its conjugate base, the acetate anion (CH3COO-), such as sodium acetate (CH3COONa)

So; Correct option is D, Acetic acid and sodium salt of acetic acid.

32. pKa is a pH at which concentration of protonated and deprotonated species is equal.

So here in this graph we can see a plateau between 4 to 8 ml of base added at pH 8 to 9.5 approximately is the buffering region of NH4Cl. Hence pKa would be 9 approximately. Option B is correct.

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