Lexan is a plastic used to make compact disks, eyeglass lenses, and bullet proof

Question

Lexan is a plastic used to make compact disks, eyeglass lenses, and bullet proof glass. One of the compounds used to make Lexan is phosgene (COCl2), an extremely poisonous gas. Phosgene decomposes by the following reaction;
COCl2(g) CO(g) + Cl2(g) Kp = 6.8 × 10-9 at 100 °C
If pure phosgene at an initial pressure of 1.0 atm decomposes, calculate the equilibrium pressures of all species.

Select one:

a. PCOCl2 = 6.8 × 10-9atm; PCO = 1.0 atm; PCl2 = 8.2 × 10-5atm

b. PCOCl2 = 8.2 × 10-5 atm; PCO = 1.0 atm; PCl2 = 1.0 atm

c. PCOCl2 = 1.0 atm; PCO = 6.8 × 10-9atm; PCl2 = 6.8 × 10-9 atm

d. PCOCl2 = 1.0 atm; PCO = 8.2 × 10-5 atm; PCl2 = 8.2 × 10-5 atm

e. none of the above

Answer b is wrong

For the following equilibrium, determine which conditions would be best to alter the equilibriums position towards products.
2SO3(g) 2SO2(g) + O2(g) DH = 198 kJ
I. Increase temperature and decrease pressure
II. Increase temperature and increase products
III. Decrease temperature and extract products from flask
IV. Increase reactants and Decrease temperature
V. Decrease temperature and increase pressure

Select one:

a. I

b. II

c. II and IV

d. IV

e. V

e is wrong

Explanation / Answer

1)

COCl2 (g)   <—>   CO (g)    +   Cl2 (g)

1.0            0           0       (initial)

1.0-x           x           x       (at equilibrium)

Kp = p(CO)*p(Cl2) / p(COCl2)

6.8*10^-9 = x*x/(1.0-x)

since Kp is small, x will be small and it can ignored as compared to 1.0

So, above expression becomes:

6.8*10^-9 = x*x/(1.0)

x^2 = 6.8*10^-9

x = 8.2*10^-5

So, at equilibrium:

p(COCl2) = 1.0-x = 1.0 atm

p(CO) = x = 8.2*10^-5 atm

p(Cl2) = x = 8.2*10^-5 atm

Answer: d

2)

Effect of Increasing Temperature:

Increasing Temperature will shift the reaction in a direction which absorbs heat as per Le chatelier Principle

Forward reaction is endothermic in nature

hence, forward reaction will be favoured

So, Equilibrium moves to product side

Effect of Decreasing Temperature:

Decreasing Temperature will shift the reaction in a direction which release heat as per Le chatelier Principle

Forward reaction is endothermic in nature

hence, backward reaction will be favoured

So, Equilibrium moves to reactant side

Effect of Increasing pressure:

Increasing pressure will shift the reaction in a direction which have lesser gaseous molecules as per Le chatelier Principle

Here reactant has less gaseous molecule

So equilibrium will move to left

So, Equilibrium moves to reactant side

Removing product will move reaction to product side

Adding reactant will move reaction to product side

Answer: a. I

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