1. What is the observed result of increasing the total pressure under isothermal

Question

1. What is the observed result of increasing the total pressure under isothermal conditions in the following system initially at equilibrium?

PCl3 (g) + Cl2 (g) <——> PCl5 (g)

a) No change in the pPCl3 to pPCl5 ratio

b) An increase in the pCl2 to pPCl5 ratio

c) A decrease in the ratio of pPCl5 to (pPCl3) x (pCl2)

d) An increase in the pPCl5 to pPCl3 ratio

________________________________________________

2. Which of the following is the result of cooling an endothermic reaction that starts at equilibrium?

a) The amount of products decreases

b) The amount of reactants decreases

c) The equilibrium constant increases

d) All partial pressure increases

___________________________________________________

3. In which of the following compounds is the oxidation state of phosphorus the GREATEST?

a) P4O5

b) P4

c) PH3

d) POCl3

Explanation / Answer

1. In the reaction, PCl3 and Cl2 combine to give PCl5, So, when the total pressure is increased, it means that the pressure of PCl3 and Cl2 is increased. According the Le-chatelier's principle, by increasing the pressure of reactants, shift the reaction towards right-hand side. This shift will eventually increase pressure of product, i.e PCl5. In the options, given the corresct answer will be (d). As the pressure of PCl5 will increase, the pressure of reactant will decrease. Thus the ratio of PCl5 to PCl3 will increase. So, the correct answer is d.

2. It is an endothermic reaction and we are cooling the process, so heat will decrease on left hand side, i.e. reactants. According to Le-chatelier's principle, this decrease will shift the reaction towards left. This shift will increase the concentration of reactants and decrease the concentration of products. So, correct answer is (a).

3. Oxidation state of P in the given compounds: Suppose oxidation state of P is x.

(a) In P4O5, oxidation state of O is -2. As the compound is neutral. So, 4(x)+5(-2)=0. This gives x= 2.5.

(b) In P4, 4(x) = 0. So, x = 0

(c) In PH3, oxidation state of H is -1. So, x+3(-1)=0. This gives x= +3.

(d) In POCl3, oxidation state of O is -2, Cl is -1. So, x+(-2)+3(-1)=0. This gives x= +5.

So, in (d), oxidation state of P is +5. So, answer is (d).

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