Question

1. When the system Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq) is at equilibrium, which one of the following statements best describes the equilibrium state?

a.neither the forward nor the reverse reaction has stopped

b.	the value of the equilibrium constant is 1

c.	the concentrations of Fe3+, SCN-, and FeSCN2+ are always equal at equilibrium

d.	both the forward and the reverse reaction has stopped

2.

Which of the following will change the value of an equilibrium constant?

I) varying the initial concentrations of reactants

II) varying the initial concentrations of products

III) changing temperature

3.

Consider the reaction: Fe3+(aq)  + SCN−(aq)  ⇌ Fe(SCN)2+(aq)

A mixture is prepared with initial Fe3+ and SCN- concentrations of 0.3 M and 0.005 M, respectively. Complete an ICE table.

Answer 1

1)

a) neither the forward nor the reverse reaction has stopped

Explanation

At equillibrium , rate of forward reaction is equal to rate of reverse reaction, so a chemical equillibrium is dynamic equillibrium. So, statement a is correct and statement d is incorrect.

Consider the general reaction at equillbrium

aA + bB <--------> cC + dD

equillibrium constant expression is

K = [C]^c[D]^d/[A]^a[B]^b

Concentration of A,B,C,and D need not be equal at equillibrium so, equillibrium concentration need not be 1. So, both statements b and c are incorrect.

2.

iii) changing temperature

Equillibrium constant is not depends on concentration, pressure,volume but it depends only on concentration.

3.

	Fe3+(aq)	SCN-(aq)	Fe(SCN)2+(aq)
Initial concentration	0.3	0.005	0
change in concentration	-x	-x	+x
equillibrium concentration	0.3 -x	0.005 -x	x