Questions and tasks for self solution

 

1. What reactions can be called: a) irreversible; b) reversible; c)direct;

d) reverse? Give the examples.

2. What difference exists between rate constants for direct and reverse reactions

3. How do the rates of direct and reverse reactions change? Why?

4. What is the chemical equilibrium? Why it is the dynamic? What concentrations of reactant are named as equilibrium?

5. What is called the constant of equilibrium? Does this value depend on nature of reactants, their concentrations, temperature, pressure?

6. Why does the numeral value of equilibrium constant define the extent of conversion of initial reagents into products.

7. Why does the expression of equilibrium constant not include the solid concentrations?

8. What parameters is the chemical equilibrium characterized by? List them.

9. What process is called as the shift of equilibrium?

10. Show, using examples, how does the equilibrium shift if there is the change of a) concentration of some reactant, b)temperature, c) pressure.

11. Rate of which reaction increases in greater extent (exo- or endothermic) if the equilibrium system is heated?

12. Does the catalyst influence on the state of equilibrium, why? Does the equilibrium constant depend on catalyst?

13. Which activation energy is more – of direct or reverse reaction, if direct reaction proceeds with heat evolving?

14. What reaction is exothermic if at given temperature rate constant of direct reaction is more then this one of reverse reaction?

15. Write down the expression for K_c for the following reactions:

a) 2NO_(g) + O_2(g)↔2NO_2(g)

b)  CH₃COOH_(solution)↔CH₃COO^-_(solution)+H⁺_(sol)

c) MgCO_3(solid) ↔ MgO_(solid) + CO_2(g)

d) [HgI₄]^2-_(solution)↔Hg²⁺_(solution)  + 4I^-_(solution)

e) H₂O_(liq) ↔ H⁺_(solution) + OH^-_(solution)

f) 3Fe_(solid) + 4H₂O_(liq)↔Fe₃O_4(solid) + 4H_2(g)

16. Equilibrium constant at 450⁰C for reaction H₂ + I₂ ↔2HI is equal to 50,0. Find the equilibrium constant for reaction of HI dissociation at the same temperature.                                                                        The answer: 0,02

17. Find the equilibrium constant for homogeneous reaction A + B ↔ C + D, if initial A and B concentrations are equal to 0,8 mol/l for each one and equilibrium concentrations of C and D are equal to 0,6 mol/l.  The answer: 9.

18. What is the equilibrium constant K_p for reaction: 2HI_(g)↔H_2(g)+I_2(g) at 448⁰C, if partial equilibrium pressures of gases at given temperature are: p(HI) = 40,5 kPa, p(H₂) = 75,2 kPa, p(I₂) = 0,436 kPa? The answer: 0,02.

19. The equilibrium for system: PCl_5(g)↔PCl_3(g) + Cl_2(g) at 500⁰K have been established, when initial PCl₅ concentration, equal 1 mol/l decreased till 0,46 mol/l Find K_c at given temperature. The answer:0,634

20. Solve for equilibrium constant: 4HCl_(g) + O_2(g)↔2Cl_2(g)  + 2H₂O_(g)  

if initial amounts of substances were 2,4 moles of HCl and 1,2 moles of O₂ but to the moment of equilibrium 0,8 moles of HCl have been remained as nonreacted. The volume of reaction vessel is equal to 4L. The answer: 5.

21. Solve for equilibrium constant of the reaction: N_2(g) + 3H_2(g)↔ 2NH_3(g), if 0,05 moles of N₂ and 0,52 moles of H₂ were introduced into reaction vessel which volume is 10 L, at some temperature and to the equilibrium moment 0,04moles of ammonia were formed.  The answer: 54,8.

22. At 650⁰C the equilibrium constant of the system CO_2(g) + H_2(g) ↔ CO_(g) + H₂O_(g)    is equal to 1. The initial concentrations of CO₂ and H₂ were 0,2 and 0,8 mol/l. Solve for equilibrium concentrations of all reactants.

The answer: 0,04; 0,64; 0,16; 0,16 mol/l.

23. The equilibrium constant for reaction FeO_(solid) + CO_(g) ↔ Fe_(solid) + CO_2(g) at 1000⁰C is equal to 0,5. The initial concentrations of CO and CO₂ were 0,05 and 0,01 mol/l. Find their equilibrium concentrations. The answer: 0,04 and 0,02 mol/l.

24. Find equilibrium constant of the reaction N₂O₄↔2NO₂, if initial concentration of N₂O₄ was 0,08 mol/l and to the equilibrium moment 50% of N₂O₄ have dissociated. The answer: 0,16.

25. Will the introducing of additional amounts of a) CO₂, b) CaCO₃ influence on the equilibrium concentration of CO₂ in the system:

CaCO_3(solid) ↔ CaO_(solid) + CO_2(g)?

26 What conditions will facilitate to the more producing of SO₃ according to the reaction SO2 + 1/2O₂↔SO₃; ∆H⁰₂₉₈ = -98,9 kJ/mol? What mass of SO₂ is consumed if SO₃ with mass 10g is formed. The answer: 8g.

27 In what side does the equilibrium shift:

     a)     2H₂S_(g)↔2H_2(g) + S_2(solid); ∆H = 40,13 kJ

b)    N₂O_4(liq)↔2NO_2(g); ∆H = 66,55 kJ

с)     CO_(g)  + H₂O_(g) ↔CO_2(g) + H_2(g); ∆ H = -40,96 kJ

              if    1) the temperature increases

                    2) the pressure increases?

28 In what side will the equilibrium shift if the temperature increases in the system:

a) N_2(g) + 3H_2(g)↔2NH_3(g), ∆H = -92,4 kJ

b) 2CO_2(g)↔2CO_(g) + O_2(g), ∆H = 556kJ

c) 4HCl_(g) + O_2(g)↔ 2Cl_2(g) + 2H₂O_(liq) , ∆H = -202,4kJ

29. How can we change the concentrations of reactants to shift the equilibrium to right: CO_2(g) + C_(coul)↔2CO_(g)

30. In what direction does the equilibrium shift A_2(g) + B_2(g)↔2AB_(g), if to increase the pressure 2 times higher and simultaneously to increase the temperature by 10⁰? Temperature coefficients of the rates of direct and reverse reactions are equal correspondingly 2 and 3. What sign of ∆H⁰ is here?        

                                                                           The answer: to left, ∆H⁰ < 0.

 

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