0.6 Reversible Reaction

How does an exothermic reversible reaction respond to heating the solution?

By shifting the equilibrium towards the reactants

For exercise number 6, when ammonia is added to the reaction at equilibrium, will products or reactants be produced? Will you see precipitate formation or solid dissolving?

favor products, dissolving the solid

In order to avoid congestion at various hoods in the lab room, you
should do which one of the following:
a. Only do the odd experiments.
b. Pairs should start at various experiments.
c. Be as quick as you can.
d. Do all experiments at your lab bench. (Don’t choose this one)

b. Pairs should start at various experiments.

Lab Purpose:

To use observations and balanced equations to determine how a reaction responds to a stress applied to it when it is at equilibrium.

A reversible reaction reaches dynamic equilibrium when (+note)

the rate of the forward reaction equals the rate of the reverse reaction (This indicates nothing about how quickly the reaction reaches equilibrium nor the amount of each species present at equilibrium)

Le Chatlier’s Principle says

A reaction at equilibrium will respond to a stress applied by shifting to relieve the stress and get back to equilibrium.

Increasing the concentration of a reactant will…

cause the reaction to make more product and vice versa

Decreasing the concentration of a product will…

cause the reaction to make more product

Increasing the pressure (by decreasing the volume) would….

cause the reaction to make less moles of gas

Increasing the temperature causes a change in…

the value of the equilibrium constant and thus a shift in the reaction

How could you remove essentially all of the magnesium ion from a solution?

Adding NaOH/ any strong base will form Mg(OH)2 which means the precipitate will remove Mg2+

How would you dissolve solid Mg(OH)2?

Since Mg(OH)2 is a base, I would react it with an acidic solution like HCl

Why is it difficult to completely precipitate aluminum ion as a hydroxide?

It is difficult because aluminum hydroxide is amphoteric

A solution contains Mg2+ and Al3+ ions. How could you separate them?

Raising the pH (adding OH-) will cause Al3+ to form Al(OH3 precipitate. Unlike Mg2+ which will stay soluble (mostly) until higher pH levels

In what form (Fe3+ or FeSCN2+) do you think that iron could be determined by
visible spectroscopy? Explain your answer

You would be able to use visual spectroscopy on FeSCN2+ because it is a darker
color than the barely visible, light colored Fe3+

A solution contains Mg2+ and Cu2+ ions. How could you separate them?

Separate them by adding NaOH which will precipitates Cu(OH)2 and Mg(OH)2 at high pH. Cu2+ will precipitate first then Mg2+. If done slowly the precipitate can be
separated

Rewrite equation (5) putting the word "heat" on the correct side.

Co(H2O)6 ^2+ (aq) + 4Cl^- (aq) + heat <=> CoCl4^2-(aq) + 6H2O (l)

What property do Ag+ and Cu2+ ions have in common?

Both of them are aqueous and can make a precipitate with ammonia

In each case indicate which reagent, hydrochloric acid or sodium hydroxide, would shift the ionic reaction in the desired direction.
a) SnS2(s) + S2– (aq) ←> SnS32– (aq) (left)
b) NH3(g) + H2O(l) ←> NH4+ (aq) + OH– (aq) (right)
c) 2 Sr2+(aq) + H2O(l) + Cr2O72– (aq) ←> 2 SrCrO4(s) + 2 H+(aq) (left)
d) H+(aq) + HCO3– (aq) ←> H2O(l) + CO2(g) (right)

a.) NaOH

b.) HCl

c.) HCl

d.)NaOH

Assuming that each of the following reversible reactions has reached a state of
equilibrium, indicate with an arrow, showing direction of shift, the effect of
each change upon the equilibrium. Assume that only one change is made at a time.

2 Cl2(g) + 2 H2O(g) + heat  4 HCl(g) + O2(g)

1.) Raise P

2.)Raise T

1.) Raise P (←)

2.) Raise T (→)

Assuming that each of the following reversible reactions has reached a state of
equilibrium, indicate with an arrow, showing direction of shift, the effect of
each change upon the equilibrium. Assume that only one change is made at a time.

Fe2O3(s) + 3 H2(g)  3 H2O(g) + 2 Fe(s)

1.)Add Fe(s)

2.) Raise P

1.)Add Fe(s): no change

2.) Raise P: no change

Assuming that each of the following reversible reactions has reached a state of
equilibrium, indicate with an arrow, showing direction of shift, the effect of
each change upon the equilibrium. Assume that only one change is made at a time.

NH3(g) + heat  N2(g) + 3 H2(g)

1.) Raise T

2.) Lower P

1.) Raise T (→)

2.) Lower P (→)

Assuming that each of the following reversible reactions has reached a state of
equilibrium, indicate with an arrow, showing direction of shift, the effect of
each change upon the equilibrium. Assume that only one change is made at a time.

CO(g) + H2O(g)  CO2(g) + H2(g) + heat

1.) Lower T

2.) Raise P

1.) Lower T (→)

2.) Raise P (no change)

Assuming that each of the following reversible reactions has reached a state of
equilibrium, indicate with an arrow, showing direction of shift, the effect of
each change upon the equilibrium. Assume that only one change is made at a time.

SO2(g) + O2(g)  2 SO3(g) + heat

1.) Raise T

2.) Lower P

1.) Raise T (←)

2.) Lower P (←)