A chemistry student needs to determine the effect of increasing the temperature on the equilibrium constant of the formation of a complex ion. Given the equation: Fe3+ + 4OH- ↔ Fe(OH)4- Kc = 2.1 x 10^-18 If the initial concentration of Fe3+ is 0.02 M and OH- is 0.1 M at 25°C, what is the new equilibrium constant at 35°C assuming the reaction is exothermic and the heat of reaction is -20 kJ/mol?

Question

A chemistry student needs to determine the effect of increasing the temperature on the equilibrium constant of the formation of a complex ion. Given the equation: Fe3+ + 4OH- ↔ Fe(OH)4-     Kc = 2.1 x 10^-18  If the initial concentration of Fe3+ is 0.02 M and OH- is 0.1 M at 25°C, what is the new equilibrium constant at 35°C assuming the reaction is exothermic and the

Answer 1

To determine the new equilibrium constant at 35C, we can use the Van't Hoff equation:ln K2/K1  = -H/R *  1/T2 - 1/T1 where K1 is the initial equilibrium constant  2.1 x 10^-18 , K2 is the new equilibrium constant, H is the heat of reaction  -20 kJ/mol , R is the gas constant  8.314 J/molK , T1 is the initial temperature  25C = 298.15 K , and T2 is the final temperature  35C = 308.15 K .First, we need to convert the heat of reaction to J/mol:H = -20 kJ/mol *  1000 J/1 kJ  = -20,000 J/molNow, we can plug the values into the Van't Hoff equation:ln K2/ 2.1 x 10^-18   = - -20,000 J/mol  /  8.314 J/molK  *  1/308.15 K - 1/298.15 K Solving for K2:ln K2/ 2.1 x 10^-18    0.961K2/ 2.1 x 10^-18   e^0.961  2.615K2  2.615 *  2.1 x 10^-18   5.49 x 10^-18So, the new equilibrium constant at 35C is approximately 5.49 x 10^-18.