Question

In an aqueous chloride solution cobalt(ii) exists in equilibrium with the complex ion cocl42-. co2 (aq) is pink and cocl42-(aq) is blue. ... at low temperature the pink color predominates. ... ... at high temperature the blue color is strong. ... if we represent the equilibrium as:... cocl42-(aq) co2 (aq) 4cl-(aq) we can conclude that: 1. this reaction is:
a. exothermic


b. endothermic


c. neutral


d. more information is needed to answer this question. 2. when the temperature is decreased the equilibrium constant, k:


a. increases


b. decreases


c. remains the same


d. more information is needed to answer this question. 3. when the temperature is decreased the equilibrium concentration of co2 :


a. increases


b. decreases


c. remains the same


d. more information is needed to answer this quest

Answer 1

First you should know that the Principle of Le Chatelier states that if a system in equilibrium is subjected to a change of conditions, it will move to a new position in order to counteract the effect that disturbed it and recover the state of equilibrium.

The variation of one or several of the following factors can alter the equilibrium condition in a chemical reaction:

• Temperature
• The pressure
• The volume
• The concentration of reactants or products

1. This reaction is: a. exothermic

The chemical equilibrium at issue is:

CoCl₄²⁻  ⇄   Co²⁺ + 4Cl⁻ + heat

blue            pink

The reaction of the question is exothermic because when adding heat (at high temperature) the equilibrium moves to the left since the blue color is strong which means that there are more reagent (CoCl₄²⁻) that product (Co²⁺). On the other hand, when extracting heat from the system (at low temperature) the equilibrium moves to the right since the pink color predominates and more product is present in the solution.

2. When the temperature is decreased the equilibrium constant, k: c. remains the same.

As mentioned above, a system in equilibrium that is disturbed will move to a new position in order to counteract the effect that disturbed it and recover the state of equilibrium. In this way, the system will always remain in equilibrium and its equilibrium constant will remain constant. This is why, despite altering the temperature of the system, the equilibrium constant remains constant.

3. When the temperature is decreased the equilibrium concentration of Co²⁺:  a. increases

Again, the chemical equilibrium at issue is:

CoCl₄²⁻  ⇄   Co²⁺ + 4Cl⁻ + heat

As the reaction in question is exothermic when the temperature decreases, heat is extracted from the system. To compensate this decrease in heat, the system will react by shifting the balance to the right, increasing the concentration of the products and, therefore, the concentration of Co²⁺.