Explain what is meant by the term dynamic equilibrium -

Question

1. (a) Explain what is meant by the term 'dynamic equilibrium'

(b) Distinguish between heterogeneous and homogeneous equilibria

2. For each of the chemical reactions below:

(a) Balance the chemical equation

(b) Write down an expression for the equilibrium constant (K_c)

(c) Determine the units of K_c(T) in each case.

            (i) CaCO₃(s)?  CaO(s)     +    CO_2(g)

            (ii) N_2(g)  +  H_2(g) ?  NH_3(g)

            (iii) N₂O_4(g)?  NO_{2 (g)}    

3. The solvent ethylethanoate is produced by the reaction of ethanoic acid with ethanol. Note that this reaction is not in aqueous solution.

CH₃COOH(l)  +  CH₃CH₂OH(l) CH₃COO CH₂CH₃ (l)  + H₂O (l)

(a) Explain why you can calculate K_c(T) without knowing the volume of the solution.

(b) Write an equilibrium expression for K_c(T).

(c) An initial solution was prepared by mixing 2.00 mol of ethanoic acid and 1.00 molof ethanolat 25°C.  A small amount of hydrochloric acid was also added to catalyse the reaction.  The solution was found to contain 0.82mol of ethylethanoate at equilibrium. Calculate the value for K_c(T). State the

(d) In a separate reaction, the equilibrium mixture was found to contain 4.00  mol of ethanoic acid, 6.00 mol of ethanol, and 12.00 mol of water at 25°C. 

How many moles of ethylethanoate (CH₃COOCH₂CH₃) were present at equilibrium?

(e) A characteristic reaction of ethylethanoate is hydrolysis, the reverse of the reaction given above.  Write the equilibrium equation for the hydrolysis of ethyl acetate and calculate K_c(T)  for the hydrolysis reaction.

4. A chemist is attempting to prepare 1,2-dichloroethane by the exothermic reaction between ethene and chlorine:

C₂H₄(g)  +   Cl₂(g)                  C₂H₄Cl₂(g)    DH = -222.2 kJ mol^-1

Use Le Chatelier's Principle to suggest three ways to increase the yield of  C₂H₄Cl₂.  Explain your reasoning.

5. State the oxidation number of the element underlined in each of the following. In your answers give the name of the element followed by its oxidation number.

a) H₃PO₄; b) NaH; c) SiO₂; d) KClO₄e) MnO₂

6. (i) Cr₂O₃(s) + 2Al(s)  à Al₂O₃(s) + 2Cr(l)

(ii) 2Fe₂O₃(s) + 3C(s) à 4Fe(l) + 3CO₂(g)

(iii) BrO₃^-(aq) +5Br^-(aq) + 6H⁺(aq) à 3Br₂(aq) + 3H₂O(l)

(iv) 2S₂O₃^2-(aq) + 2H⁺(aq)   ®  2HSO₃^-(aq) + 2S(s) + 2H₂O(l)

a) For each of the reactions above identify which species is being reduced.

b) For each of the reactions above, identify which is the reducing agent.

c) Identify and explain the type of reaction shown in (iv).

7. In a redox reaction, dichromate (VI) ions,Cr₂O₇^2-,  are reduced to chromium(III) ions Cr³⁺ in dilute sulphuric acid. Dichromate (VI) acts as an oxidising agent to convert iron (II), Fe²⁺, to iron (III), Fe³⁺.

a) Write

(i) the balanced oxidising half equation

(ii) the balanced reducing half equation for this process. You will need to consider the role of the acid in the reaction.

b) Combine these two equations, and give a balanced equation for the overall process. All species are in aqueous solution.