Equilibrium
- Higher yield of NO in N_2(g) + O_2(g) ⇌ 2NO(g) can be obtained at[Δ H of the reaction = + 180.7 kJ mol^-1]A. higher temperatureB. lower temperatureC. higher concentration of N_2D. higher concentration of O_2Choose the correct answer from the options… Answer: 4. A, C, D only Key idea: Le Chatelier's principle. Δ H>0 (endothermic): higher temperature favours NO, so A is right and B is wrong... 1
- For the reaction A(g) ⇌ 2B(g), the backward reaction rate constant is higher than the forward reaction rate constant by a factor of 2500, at 1000 K.[Given : R = 0.0831 L atm mol^-1 K^-1]K_p for the reaction at 1000 K is Answer: 3. 0.033 Key idea: K_c=k_f/k_b and K_p=K_c(RT)^(Δ n) . k_b=2500 k_f , so K_c=1/2500=4×10⁻⁴ . Δ n=2-1=1 ; RT=0.0831×1000=83.1 . K_p=4... 1
- Phosphoric acid ionizes in three steps with ionization constant values K_a_1, K_a_2 and K_a_3, respectively, while K is the overall ionization constant. Which of the following statements are true?A. K = K_a_1 + K_a_2 + K_a_3B. H_3PO_4 is a stronger a… Answer: 4. A, B and C only Key idea: overall K=K_(a_1)K_(a_2)K_(a_3) , and each successive ionization is harder. A true: taking logs, log K=... 1
- Consider the following reaction in a sealed vessel at equilibrium with concentrations of N_2 = 3.0×10^-3 M, O_2 = 4.2×10^-3 M and NO = 2.8×10^-3 M.2NO_(g) ⇌ N_2(g) + O_2(g)If 0.1 mol L^-1 of NO_(g) is taken in a closed vessel, what will be degree of… Answer: 1. 0.717 Key idea: get K_c from the first data set, then use it for the new mixture. K_c=[N₂][O₂]/[NO]²=frac(3.0×10⁻³)(4.2×10⁻³)(2.8... 1
- The Henry's law constant (K_H) values of three gases (A, B, C) in water are 145, 2×10^-5 and 35 kbar, respectively. The solubility of these gases in water follow the order: Answer: 3. B > C > A Key idea: by Henry's law p=K_Hx , so a larger K_H means lower solubility. K_H : B ( 2×10⁻⁵ ) < C (35) < A (145) kbar. S... 1
- For the reaction 2A ⇌ B + C, K_c = 4×10^-3. At a given time, the composition of reaction mixture is : [A]=[B]=[C]=2×10^-3 M.Then, which of the following is correct? Answer: 4. Reaction has a tendency to go in backward direction. Key idea: compare the reaction quotient Q_c with K_c . Q_c=[B][C]/[A]²=frac(... 1
- In which of the following equilibria, K_p and K_c are NOT equal? Answer: 2. PCl_(5(g)) ⇌ PCl_(3(g)) + Cl_(2(g)) Key idea: K_p=K_c(RT)^(Δ n_g) . They are equal only when Δ n_g=0 . 2BrCl⇌ Br₂+Cl₂ : Δ n_g=0 .... 1
- Amongst the given options which of the following molecules / ion acts as a Lewis acid? Answer: 4. BF ₃ Key idea: A Lewis acid accepts an electron pair. BF₃ has an incomplete octet on boron (6 electrons) and an empty p orbital,... 1
- Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :Assertion A : Helium is used to dilute oxygen in diving apparatus.Reasons R : Helium has high solubility in O_2.In the light of the above statement… Answer: 4. A is true but R is false. Key idea: Gases dissolve in blood at high pressure; helium is chosen because it is hardly soluble. Asse... 1
- 3O_2(g) ⇌ 2O_3(g)for the above reaction at 298 K, K_c is found to be 3.0 × 10^-59. If the concentration of O_2 at equilibrium is 0.040 M then concentration of O_3 in M is Answer: 2. 4.38 × 10⁻³² Key idea: K_c=[O₃]²/[O₂]³ . [O₃]²=3.0×10⁻⁵⁹×(0.040)³=3.0×10⁻⁵⁹×6.4×10⁻⁵=1.92×10⁻⁶³ . [O₃]=sqrt1.92×10⁻⁶³=4.38×10⁻³²... 1
- The pH of the solution containing 50 mL each of 0.10 M sodium acetate and 0.01 M acetic acid is[Given pK_a of CH_3COOH = 4.57] Answer: 2. 5.57 Key idea: acetate/acetic acid is an acidic buffer; use the Henderson equation. pH=pK_a+log[salt]/[acid] Equal volumes are mi... 1
- The pK_b of dimethylamine and pK_a of acetic acid are 3.27 and 4.77 respectively at T (K). The correct option for the pH of dimethylammonium acetate solution is : Answer: 3. 7.75 Key idea: for a salt of a weak acid and a weak base, pH=7+1/2(pK_a-pK_b) . pH=7+1/2(4.77-3.27)=7+0.75=7.75 . 1
- HCl was passed through a solution of CaCl_2, MgCl_2 and NaCl. Which of the following compound(s) crystallise(s) ? Answer: 2. Only NaCl Passing HCl gas raises the Cl^- concentration. When the ionic product [Na^+][Cl^-] exceeds the solubility product of Na... 1
- Find out the solubility of Ni(OH)_2 in 0.1 M NaOH. Given that the ionic product of Ni(OH)_2 is 2×10^-15. Answer: 1. 2×10⁻¹³ M In 0.1 M NaOH the common ion OH^- is already present, so the OH^- from Ni(OH)₂ can be ignored. mathrmNi(OH)₂ ⇌ Ni²⁺ + 2... 1
- Which will make basic buffer ? Answer: 3. 100 mL of 0.1 M HCl + 200 mL of 0.1 M NH ₄ OH A basic buffer is a weak base plus its salt (conjugate acid). (1) 5 mmol NaOH + 2.5... 1
- Conjugate base for Brönsted acids H_2O and HF are : Answer: 3. OH ^- and F ^- , respectively A conjugate base is formed when the acid loses H^+ . H₂O → OH^- + H^+ and HF → F^- + H^+ . So the c... 1
- pH of a saturated solution of Ca(OH)_2 is 9. The solubility product (K_sp) of Ca(OH)_2 is : Answer: 1. 0.5×10⁻¹⁵ Use pH to get [OH^-] , then write K_sp . pH = 9 so pOH = 5 and [OH^-] = 10⁻⁵ M. mathrmCa(OH)₂ ⇌ Ca²⁺ + 2OH^- , so [math... 1
- Which one of the following conditions will favour maximum formation of the product in the reaction,A_2(g) + B_2(g) ⇌ X_2(g) Δ_rH = -X kJ ? Answer: 1. Low temperature and high pressure Apply Le Chatelier's principle to A₂+B₂⇌ X₂ , which is exothermic and reduces the number of gas... 1
- The correction factor 'a' to the ideal gas equation corresponds to Answer: 4. forces of attraction between the gas molecules In the van der Waals equation (P+an²/V²)(V-nb)=nRT , the term a corrects the press... 1
- Given van der Waals constant for NH_3, H_2, O_2 and CO_2 are respectively 4.17, 0.244, 1.36 and 3.59, which one of the following gases is most easily liquefied ? Answer: 1. NH ₃ The more easily a gas liquefies, the stronger its intermolecular attraction, and the van der Waals constant a measures exact... 1
- Following solutions were prepared by mixing different volumes of NaOH and HCl of different concentrations :a. 60 mL M/10 HCl + 40 mL M/10 NaOHb. 55 mL M/10 HCl + 45 mL M/10 NaOHc. 75 mL M/5 HCl + 25 mL M/5 NaOHd. 100 mL M/10 HCl + 100 mL M/10 NaOHpH… Answer: 4. c pH = 1 means [H^+]=0.1 M, so excess strong acid of that concentration must remain after mixing. a: HCl 6 mmol, NaOH 4 mmol, exc... 1
- The solubility of BaSO_4 in water is 2.42×10^-3 gL^-1 at 298 K. The value of its solubility product (K_sp) will be(Given molar mass of BaSO_4 = 233 g mol^-1) Answer: 1. 1.08×10⁻¹⁰ mol ² L ⁻² Convert solubility to mol/L, then use K_sp=s² for a 1:1 salt. s=dfrac2.42×10⁻³233=1.04×10⁻⁵\ mathrmmol L⁻¹... 1
- Concentration of the Ag^+ ions in a saturated solution of Ag_2C_2O_4 is 2.2 × 10^-4 mol L^-1. Solubility product of Ag_2C_2O_4 is : Answer: 3. 5.3 × 10⁻¹² Key idea: Ag₂C₂O₄ ⇌ 2Ag^+ + C₂O₄²⁻ , K_sp=[Ag^+]²[C₂O₄²⁻] . [C₂O₄²⁻]=1/2[Ag^+]=1.1×10⁻⁴ M. K_sp=(2.2×10⁻⁴)²×1.1×10⁻⁴=... 1
- The equilibrium constants of the following are :N_2 + 3H_2 ⇌ 2NH_3 K_1N_2 + O_2 ⇌ 2NO K_2H_2 + 1/2O_2 → H_2O K_3The equilibrium constant (K) of the reaction : 2NH_3 + 5/2O_2 K⇌ 2NO + 3H_2O, will be : Answer: 1. K₂K₃³/K₁ Key idea: combine reactions; reversing gives 1/K , multiplying by n gives Kⁿ , adding gives the product of K values. Tar... 1