Question

The following reaction is the Haber process used to make ammonia from its elements.

Use this information for questions 1 & 2              

N₂(g) + 3H₂(g) <--> 2NH₃(g)              DH^o = +92 kJ

___1. Suppose the reaction flask is already at equilibrium, but then the volume of the reaction flask is then reduced.

What will happen?

a) [NH₃] will lower.                                              c) The reaction will proceed right.

b) [Reactants] will increase                          d) Nothing will occur. It will stay at equilibrium.

___2. Suppose the reaction flask is already at equilibrium, but instead of changing the flask size, we add some extra heat to the flask.   What will happen?

a) [NH₃] will lower.                                                                c) The partial pressure of hydrogen will increase.

b) Kc will actually decrease.                                          d) The partial pressure of ammonia will increase.

___4. What does it mean when the reaction quotient is found to be smaller than the equilibrium constant?

                  a) To push the reaction to more products, we need to change the flask size.

                  b) The DG^o is almost equal to zero.

                  c) The reaction will shift to the left to reach equilibrium.

                  d) The reaction is incomplete and will still move forward.

___ 6. If I found a solution with a pH of 4.11, then the proper hydronium ion concentration must be:

                  a) 1.3 x 10^-10 M                                                        d) 7.8 x10^-5 M

                  b) 1.29 1.3 x 10^-10 M                                             e) 7.76 x10^-5 M

                  c) 1.288 x 10^-10 M                                                   f) 7.762 x10^-5 M

___ 9.     It is not surprising that HOCl is a stronger acid than HOBr. This trend can be explained by:

a) the electronegativity of the oxygen                                       c) the size of the halogen atom

b) the electronegativity of the halogen                                     d) the number of protons in the halogen

___ 10. Give the pH for a 55 mM solution of strontium hydroxide.

                  a) 0.26                    b) 1.25                  c)12.74 d) 13.04                 e) 13.74

                  f) an answer not given (show it: _____________)

FILL IN THE BLANK/SHORT ANSWER (each one is labeled for point value)

1. (8) Dimethylamine does equilibrate with water.   a) Clearly and officially write this equilibrium reaction.

__________________________________<-->_______________________________________

b) The equilibrium constant for the above reaction statement is described as being a K_____.

c) If I was asked to describe this species’ strength to another person, I would describe it to be

d) If I was asked to describe the nature of the DG^o for this equilibrium to another person, I would describe it as

(and saying a sign is not sufficiently informative.

e) The Keq value for the conjugate species of dimethylamine is __________________________________.

f) Give me a name for this conjugate form.____________________________________________.

Answer 1

All these can be explain using Le-Chatlier principle

According to Le-chatlier principle, If a reaction in equilibrium is subjected to a change in concentration, temperature, pressure or volume,then equilibrium will shift in a direction to undo the effect of change.

In the given reaction, all are in gaseous form

total Number of moles of gaseous reactant = 4

Total moles of gaseous product = 2

1. Volume is reduced and Volume is inversely proportional to the Pressure.

Now, Volume is reduced. So, Pressure is increased

Pressure Number of moles

i.e. More is the pressure , more is the number of moles and vice-vers

THus, According to Le-Chatlier Principle, reaction will shift forward to reduce the pressure.

Hence option c is correct.

2. Given Value is Positive, thus reaction is endothermic reaction and if we add more heat then reaction will shift to absord this added reaction. Hence More reactants react to give the products. NH₃ increases and thus its partial pressure increases.

Hence option d is correct.

4.reaction quotient = (product of concentration of Products term raise to the power their cofficients)/

(product of concentration of reactants term raise to the power their cofficients)

NOw if reaction quotient is less than K, then it will move forward to become equal to K

Thus, option d is correct.

6. pH = -log[H⁺]

4.11 =-log[H⁺]

[H⁺] = antilog(-4.11) = 7.76*10^-5M

option e is correct.

9. HOCl is more stronger acid than HOBr because Cl is more electronegative than Br.Hence it will attract electrons from O more strongly than Br which further attracts electrons of O-H bond.

So, option b is correct.

10. 1 mol of Sr(OH)₂ given 2 mol of OH^-

SO, [OH^-] = 2*55mM =0.110M

pOH = -log[OH^-] = -log(0.110) = 0.96

pH = 14-pOH =14 -0.96 = 13.04

option d is corect