The addition of an inert gas like helium does not change the partial pressure of the products or reactants. As a result, the equilibrium concentrations do not change.

In exothermic process heat is released during the reaction.

Heat can be considered a product in this situation, and thus increasing the amount of heat in the vessel after the system has reached equilibrium will drive the reaction to the left. This property is a derivative of Le Chatelier's principle.

This reaction is exothermic, since heat is released in the reaction. In exothermic reactions, decreasing the temperature favors the forward (exothermic) reaction, while increasing the temperature favors the reverse (endothermic) reaction. Similarly, for an endothermic reaction decreasing the temperature favors the reverse (exothermic) reaction, while increasing the temperature favors the forwards (endothermic) reaction.

In this question, increasing the temperature will favor the reverse reaction, increasing the reactant concentration and decreasing the product concentration.

This reaction is at equilibrium until it is disturbed by a sudden volume change. Since the volume is decreased, the pressure on the container's contents will increase. According to Le Chatelier's principle, an increase in pressure will cause the reaction to shift toward the side that contains fewer gas particles.

In this reaction, there are three moles of gas in the reactants and two moles of gas in the products. A decrease in volume, or increase in pressure, will shift the reaction to the right, toward the product .

Remember that the concentration of the salt is not included in the solubility product constant equation, because it is a solid. Only the ion concentrations can affect the solubility of the salt in solution. When the solution is saturated, adding more salt will do nothing to the concentration of ions in the solution.

Scandium hydroxide dissociates according to this reaction.

As 0.1N HCl is added, it will quantitatively react with hydroxide anions to produce ScCl₃ and water.

Hydroxide will be removed from the above equilibrium, and the system will compensate by shifting the equilibrium to the right, according Le Chatelier's principle. As the equilibrium shifts to the right, more solid scandium hydroxide is hydrolyzed, resulting in increased solubility.

Since the system is originally at equilibrium and a stress is applied, Le Chatelier's principle is to be considered. By increasing the total pressure, the reaction will move in the direction toward which there are less molecules of gas.

Looking at the original reaction there are two moles of gas on the left and only one on the right, indicating that the reaction will shift to the right if the pressure is increased.

If lead nitrate is added to the reaction, it will dissociate into lead ions and nitrate ions. Because of the common ion effect, adding additional lead ions to the reaction will shift the reaction to the left and reduce the production of lead and chromate concentrations, keeping the solubility constant the same. (This is in accordance with Le Chatelier's principle.)

Adding sodium chromate increases the concentration of chromate ion in the solution, which shifts the reaction to the left due to the common ion effect. Thus, the solubility of lead chromate would decrease, as there would be an increased amount of solid lead chromate.  

Us the solubility constant to calculate the answer to this question. We know that:

and

Since  is a very small number, we can assume that the concentration of chromate, , will be very small compared to the concentration of the added lead, 0.019 M. We can use the two known values ( and lead concentration) to solve for the unknown chromate concentration: