The table below contains equilibrium concentration data (in molarity) for each s

Question

The table below contains equilibrium concentration data (in molarity) for each species present when atomic phosphorus gas combines with molecular chlorine gas to form gaseous phosphorus trichloride at 25 degree C. Calculate the equilibrium constant for each test. Balance the following equilibrium and name each species present. Describe and explain the color change to the above equilibrium when hellips Adding concentrated HCI Adding solid sodium chromate (Na_2CrO_4) Adding excess NaOH Write the net ionic equation to support the answer in c.) above.

Explanation / Answer

1. Test-1:

The balanced reaction in equilibrium can be written as

2P(g) + 3Cl2(g) --> 2PCl3(g)

at eqm(M): 1.195 1.553 0.532

Now equilibrium constant K can be calculated as

K = [PCl3(g)]2 / ([P(g)]2x[Cl2(g)]3) = (0.532)2 / [(1.195)2x(1.553)3] = 0.0529

Test-2:

The balanced reaction in equilibrium can be written as

2P(g) + 3Cl2(g) --> 2PCl3(g)

at eqm(M): 0.1290 0.2670 0.00395

Now equilibrium constant K can be calculated as

K = [PCl3(g)]2 / ([P(g)]2x[Cl2(g)]3) = (0.00395)2 / [(0.1290)2x(0.2670)3] = 0.0493

Test-3: K = [PCl3(g)]2 / ([P(g)]2x[Cl2(g)]3) = (0.138)2 / [(0.0812)2x(3.861)3] = 0.0502

Test-4: K = [PCl3(g)]2 / ([P(g)]2x[Cl2(g)]3) = (15.38)2 / [(1.920)2x(10.74)3] = 0.0518

2.The given unbalanced equilibrium reaction is

CrO42-(aq, yellow) + H3O+(aq) --> Cr2O72-(aq, orange) + H2O(l)

We can balance this reaction by normal heat trail method. We need to multiply CrO42- by 2 to balance Cr, H3O+(aq) by 2 and H2O by 3 to balance H and O. Hence the balanced reaction is

2CrO42-(aq, yellow) + 2H3O+(aq) --> Cr2O72-(aq, orange) + 3H2O(l) (answer)

3: (a) When HCl is added, H3O+(aq) will increase and hence the reaction will move towards product and hence the colour change is orange.

(b)When Na2CrO4 is added, the concentration of CrO42-(aq, yellow) increases and hence the equilibrium will shift towards the product. Hence the color change is orange.

(c) When ecess NaOH is added it neutralizes H3O+ decreasing its concentration. Hence the equilibrium will shift towards reactant and more H3O+ and CrO42-(aq, yellow) will be formed. Hence colour change is yellow.

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