Law of chemical equilibrium, Kp and Kc
- 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
- 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
- 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
- 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 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
- Which one of the following statements is not correct ? Answer: 1. The value of equilibrium constant is changed in the presence of a catalyst in the reaction at equilibrium. Key idea: a catalyst c... 1
- A 20 litre container at 400 K contains CO_2(g) at pressure 0.4 atm and an excess of SrO (neglect the volume of solid SrO). The volume of the container is now decreased by moving the movable piston fitted in the container. The maximum volume of the co… Answer: 4. 5 litre Key idea: for SrCO₃(s)⇌ SrO(s)+CO₂(g) , K_p = p_(CO_2) at equilibrium, so the maximum pressure of CO₂ is 1.6 atm. Initial... 1