Question

For the reaction PC15 (8) PC13 (g) + Cl2 (g) K = 0.0454 at 261 °C. If a vessel is filled with these gases such that the initial concentrations are [PC15) = 0.20 M, [PC13] = 0.20 M, and (Cl21 = 2.5 M, in which direction will a reaction occur and why? A) toward products because Qc = 0.56 B) toward reactants because Qc = 2.5 C) toward products because Qc = 2.8 D) toward reactants because Qc = 0.0454 E) it is at equilibrium because Qc = 1

Answer 1

Answer: The reaction proceed toward reactants because
`Q_c` is 2.5

Step-by-step explanation:

`K_c` is the constant of a certain reaction at equilibrium while
`Q_c` is the quotient of activities of products and reactants at any stage other than equilibrium of a reaction.

For the given chemical reaction:

`PCl_5(g)\rightleftharpoons PCl_3(g)+Cl_2(g)`

The expression of
`Q_c` for above equation follows:

`Q_c=([PCl_3][Cl_2])/([PCl_5])`

We are given:

`[PCl_3]=0.20M`

`[Cl_2]=2.5M`

`[PCl_5]=0.20M`

Putting values in above equation, we get:

`Q_c=(0.20* 2.5)/(0.20)=2.5`

We are given:

`K_c=0.0454`

There are 3 conditions:

• When
  `K_(c)>Q_c`; the reaction is product favored.
• When
  `K_(c)<Q_c`; the reaction is reactant favored.
• When
  `K_(c)=Q_c`; the reaction is in equilibrium.

As,
`Q_c>K_c`, the reaction will be favoring reactant side.

Hence, the reaction proceed toward reactants because
`Q_c` is 2.5

Answer 2

The correct answer is B.

The
`K_(eq)` is samller than
`Q` of the reaction . So,the reaction will shift towards the left i.e. towards the reactant side.

Step-by-step explanation:

Equilibrium constant is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric ratios. It is expressed as
`K_(eq)`

K is the constant of a certain reaction when it is in equilibrium, while Q is the quotient of activities of products and reactants at any stage other than equilibrium of a reaction.

For the given chemical reaction:

`PCl_5(g)\rightleftharpoons PCl_3(g)+Cl_2(g)`

The expression for
`Q` is written as:

`Q=([PCl_3][Cl_2])/([[PCl_5]^1)`

`Q=(0.20 M* 2.5 M)/(0.20 M)`

`Q=2.5`

Given :
`K_(eq)` = 0.0454

Thus as
`K_(eq)<Q`, the reaction will shift towards the left i.e. towards the reactant side.