Consider the exothermic reaction CoCl42-(aq) + 6 H2O(l) --> Co(H2O)62+(aq) + 4 Cl -(aq). Will the equilibrium concentration of CoCl42- increase or decrease when the following changes occur?
(a) HCl is added.
increases
decreases
.(b) Co(NO3)2 is added.
increases
decreases
.(c) The solution is diluted with water.
decreases
increases
.(d) The temperature is increased.
increases
decreases
Thanks
To determine how the equilibrium concentration of CoCl42- will change in each scenario, we need to analyze the effect of each change on the reaction. Let's go through each scenario:
(a) HCl is added:
HCl is a strong acid and will dissociate in water to produce H+ ions. The additional H+ ions will shift the equilibrium to the left to consume the excess H+ ions. This means that the concentration of CoCl42- will decrease.
(b) Co(NO3)2 is added:
Co(NO3)2 will dissociate in water to produce Co2+ ions. The additional Co2+ ions will react with Cl- ions to form CoCl42-, shifting the equilibrium to the right. This means that the concentration of CoCl42- will increase.
(c) The solution is diluted with water:
When the solution is diluted, the overall concentration of all species decreases. According to Le Chatelier's principle, the reaction will shift in the direction that will increase the concentration of the species with fewer moles. Since dilution does not affect the number of moles of any species in the reaction, the equilibrium will not shift. Therefore, the concentration of CoCl42- will remain unchanged.
(d) The temperature is increased:
This reaction is exothermic, which means it releases heat. According to Le Chatelier's principle, when the temperature is increased, the reaction will shift in the endothermic direction to counteract the added heat. Since the reaction is exothermic, the forward direction is the exothermic direction, which means the reaction will shift to the left. This will result in a decrease in the concentration of CoCl42-.
Therefore, the equilibrium concentration of CoCl42- will decrease in scenario (a) when HCl is added, increase in scenario (b) when Co(NO3)2 is added, remain unchanged in scenario (c) when the solution is diluted, and decrease in scenario (d) when the temperature is increased.
(a) When HCl is added, it will increase the concentration of Cl- ions in the solution. According to Le Chatelier's principle, adding more Cl- ions will shift the equilibrium towards the reactants' side to counteract the increase. Therefore, the equilibrium concentration of CoCl42- will decrease.
(b) When Co(NO3)2 is added, it will increase the concentration of Co2+ ions in the solution. According to Le Chatelier's principle, adding more Co2+ ions will shift the equilibrium towards the products' side to counteract the increase. Therefore, the equilibrium concentration of CoCl42- will increase.
(c) When the solution is diluted with water, it will decrease the concentration of all species present in the solution. According to Le Chatelier's principle, decreasing the concentration of reactants will shift the equilibrium towards the products' side to counteract the decrease. Therefore, the equilibrium concentration of CoCl42- will increase.
(d) When the temperature is increased, it will favor the endothermic reaction. Since the given reaction is exothermic, according to Le Chatelier's principle, increasing the temperature will shift the equilibrium towards the reactants' side. Therefore, the equilibrium concentration of CoCl42- will decrease.