Question

ASAP.

I ) NaCl (s) = Na+ (aq)   + Cl- (aq)

^^^What is the stress and which direction should the equilibrium shift?

III ) Fe+3(aq) + SCN-(aq) = Fe(SCN)+2(aq)

^^^What is the stress and which direction should the equilibrium shift

IV) 2CrO4 –2(aq)    +   2H+ (aq) = Cr2O7 –2(aq)    +    H2O(l)

^^^What is the stress and which direction should the equilibrium shift?

Answer 1

1. if the equilibrium constant Kc = kf/kb is always K>>1, Formation of prodcuts is favored. k<<1 formation of reactants are favored.

These effects are present when the two opposing reactions are of different molecularity. In solution, volume changes can be achieved by addition of solvent. Changing the volume effectively changes concentration. Adding more solvent is essentially a dilution. If the number of solute species on the reactant side is not the same as on the product side, then volume changes can cause a shift in equilibrium. Increasing the volume favors the process with lower molecularity. Increasing the volume then will cause the system to shift in the direction that increases the number of solute species. This is the same for reactions involving gases. Decreasing the volume of the container causes an equilibrium mixture of gases to shift in the direction that reduces the number of moles of gas. For gases, increasing the pressure by adding one of the gases participating in the reaction, will also disturb equilibrium (This is essentially a change in reactant or product concentration). Increasing the total pressure of a reaction vessel by adding a spectator gas does not affect equilibrium. Remember that volume changes can only have effect if the number of solute species or gas species in the reactant side is not equal to the if the number of solute species or gas species in the product side.

2. Usually only reactions involving gases are altered by pressure changes. Gas pressure results from gas molecules banging against the walls of the container. If you handle gases you know that gas molecules "seek" low pressure. Compressed gas "escapes" high pressure in a balloon or out of a tire valve stem. Low pressure also goes with fewer molecules of gas. If the pressure is on an equilibrium is increased the system will shift to lower the pressure. The lower number of gas molecules uses less space or volume. This favors the side of the reaction with fewer molecules.

The forward rate would be greater than the reverse rate.Adding excess of HCL no precipitation takes forming takes place

2. The yellowish dark color turns to dark red

Stress on concentrations of reactants side, because of too much Fe3+ in order to restablish equilibrium the reaction would shifted to right to used up the ecxess Fe3+ and [ Fe (SCN)]^2- The color of the solution change from yellowish orange to red color.

3.      This is a dynamic equilibrium and as such is sensitive to the acidity or basicity of the solution. Shifting the equilibrium with pH changes is a classic example of Le Chatelier’s principle at work.

     Le Chatelier's principle states that if a chemical dynamic equilibrium is disturbed by changing the conditions (concentration, temperature, volume or pressure), the position of equilibrium moves to counteract the imposed change. So if more reactant is added, the equilibrium shifts to the right in order to consume that extra reactant, which results in more product; also if the product is removed from the system, the equilibrium shifts to the right completely increasing the yield.

     Yellow chromate and orange dichromate are in equilibrium with each other in aqueous solution. The more acidic the solution, the more the equilibrium is shifted to the left towards the dichromate ion. As hydrochloric acid is added to the chromate solution, the yellow color turns to orange. Increasing the hydrogen ion concentration is shifting the equilibrium to the left in accordance with Le Chatelier's principle, where we expect the reaction to try remove some of the H⁺ we have added by reacting with the CrO₄^2-, and yielding more Cr₂O₇^2- which we observe as color change.

    When sodium hydroxide is added to the dichromate solution, the orange color turns back to yellow, hydroxide ions react with hydrogen ions forming water, driving the equilibrium to the right (OH^- removes H⁺ ions by neutralizing them and the system acts to counteract the change) and further shifting the color. We can observe that the addition of hydroxide ions promotes the conversion of dichromate to chromate.

     Acids and bases are added to a system so as to shift the position of a chemical equilibrium. The ions have different colors, so that changes are detected visually. Yellow chromate ion turns orange by addition of acid, while the orange dichromate in reaction with bases turns yellow. The equilibrium depends on the acidity of the solution, so the color in this case is pH dependent.

     Successive addition of sodium hydroxide and hydrochloric acid causes alternative changes in solution color, during which the color intensity fades due to dilution.

     The addition of concentrated acids, such as sulfuric acid into chromate/dichromate solution causes further shifting of the equilibrium, and more intense colors, turning the solution to carmine-red.