Equilibrium P1 help

[allthebest]

I am having difficulties while answering these question. 

1. The equilibrium between nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, is shown below.

                                                    2NO2(g)  (reversible sign)  N2O4(g)                      Kc = 0.01

          What happens when the volume of a mixture at equilibrium is decreased at a constant temperature?

I.       The value of Kc increases

II.      More N2O4 is formed

III.     The ratio of [NO2]/[N2O4] decreases 

A.      I and II only

B.      I and III only

C.      II and III only

D.      I, II and III

 

The answer is C. Please help me by explaining why it is C.

I know that the value of Kc doesn't increase because Kc is only affected by temperature. But I don't know the relationship between change in volume and equilibrium. Why is there more N2O4? and why does the ratio decrease?

2. 

For the following reaction Kc = 1.0 × 10–5 at 30 °C.

                                                        2NOCl(g)  2NO(g) + Cl2(g)

          Which relationship is correct at equilibrium at this temperature?

A.      The concentration of NO equals the concentration of NOCl.

B.      The concentration of NOCl is double the concentration of Cl2.

C.      The concentration of NOCl is much greater than the concentration of Cl2.

D.      The concentration of NO is much greater than the concentration of NOCl.

ANS: C

3. 

Which statement is correct for a crystal of iron(II) sulfate in a state of equilibrium with a saturated solution of iron(II) sulfate?

                                       

A.      The colour of the solution darkens as the crystal continues to dissolve.

B.      The concentration of the iron(II) sulfate solution increases as the water evaporates.

C.      The shape of the iron(II) sulfate crystal does not change.

D.      The colour of the solution does not change but the shape of the crystal may change.

ANS: D

4. Which statements about a liquid are correct?

I.       When the temperature of a liquid in a closed container increases, its vapour pressure increases.

II.      When the pressure on a liquid increases, its boiling point increases.

III.     When the pressure on a liquid increases, its vapour pressure increases.

A.      I and II only

B.      I and III only

C.      II and III only

D.      I, II and III

ANS: A

What is equilibrium vapor pressure?

5. Which statement is correct for the equilibrium H2O(l)  H2O(g) in a closed system at 100 °C?

A.      All the H2O(l) molecules have been converted to H2O(g).

B.      The rate of the forward reaction is greater than the rate of the reverse reaction.

C.      The rate of the forward reaction is less than the rate of the reverse reaction.

D.      The pressure remains constant.

ANS: D 

 

Thanks in advance

Edited August 2, 2016 by allthebest

[Msj Chem]

1) As the volume decreases (at constant temperature), the pressure increases. The equilibrium will shift to the side with the fewer gaseous molecules (in this case the products side). Therefore more N2O4 is produced. More N2O4 means with ratio of NO2/N2O4 will decrease. 

2) The very small value for the Kc means the equilibrium lies very much to the left (reactants side). Therefore the concentration of NOCl is much greater than the concentration of Cl2. 

3) At equilibrium there is no change in macroscopic properties such as colour.

4) Equilibrium vapour pressure is the pressure exerted by a vapour on a liquid at equilibrium. This question is from the old syllabus. Vapour pressure is not covered in the new syllabus. 

 

Edited August 2, 2016 by Msj Chem

[allthebest]

23 hours ago, Msj Chem said:

1) As the volume decreases (at constant temperature), the pressure increases. The equilibrium will shift to the side with the fewer gaseous molecules (in this case the products side). Therefore more N2O4 is produced. More N2O4 means with ratio of NO2/N2O4 will decrease. 

2) The very small value for the Kc means the equilibrium lies very much to the left (reactants side). Therefore the concentration of NOCl is much greater than the concentration of Cl2. 

3) At equilibrium there is no change in macroscopic properties such as colour.

4) Equilibrium vapour pressure is the pressure exerted by a vapour on a liquid at equilibrium. This question is from the old syllabus. Vapour pressure is not covered in the new syllabus. 

 

thank you very much!