Pre-Lab Questions 1·True or False: At equilibrium, no more reactants are transfo

Question

Pre-Lab Questions 1·True or False: At equilibrium, no more reactants are transformed into products. If false, rewrite the statement so that it correctly describes the nature of chemical equilibrium. 2·True or False: At equilibrium, the concentrations of reactants and products are equal. If false, rewrite the statement so that it correctly describes the nature of chemical equilibrium. 3. Paper coated with cobalt chloride is sold commercially as moisture-sensitive test strips to estimate relative humidity levels between 20 and 80 percent in air. The following reversible reaction takes place with water: CoCl2(s) + H20(g) CoC12-6H20(s) Pink Blue (a) what color do you think the paper will be when the humidity is low (20%)? What color will it be when the humidity is high (80%)? (b) The test strips come with a color chart to estimate intermediate humidity levels. Predict the intermediate color that might be observed when the humidity is about 50%.

Explanation / Answer

1. Statement 1 is false. Actually more accurate statement is that "In equilibrium state both forward & backward reaction occurrs at same rate thus concentration of both reactant & products remain constant." Clearly, in equilibrium state reactants are converting to products but backward reaction also occurs at same rate & products get converted to reactant by backward reaction. Thus there is no change in concentration of products & reactants.

2. Statement 2 is false. Correct statement is that at equilibrium concentration of product & reactant remains constant & concentrations of reactant & product are such that both forward & backward reaction occurrs at same rate".

3. Part a : Since concentration of H2O(g) is low as relative humidity is 20%, backward reaction giving CoCL2 (s) & H2O(g) shall take place at faster rate in order to reach equilibrium. Thus colour of paper shall be blue.

Similarly, when concentration of H2O(g) is high as relative humidity is 80%, forward reaction giving CoCL2.6H2O (s) shall occur at faster rate in order to reach equilibrium. Thus colour of paper shall be pink.

Part b: On reaction with water at intermediate level of 50% RH, CoCL2.2H2O (s) should form which is purple in colour. Thus colour of paper should be purple.

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