Question

A chemistry student wants to determine the effect of temperature on the ionization constant (Ka) of a weak acid. The initial Ka of the acid is 1.32 × 10^-6 at 25°C. If the temperature is increased to 35°C, calculate the new value of Ka for the weak acid.

Answer 1

To calculate the new value of Ka for the weak acid at 35C, we can use the Van't Hoff equation, which relates the temperature dependence of the equilibrium constant  Ka  to the enthalpy change  H  of the reaction:ln Ka2/Ka1  = -H/R *  1/T2 - 1/T1 Where:Ka1 is the initial ionization constant at 25C  1.32  10^-6 Ka2 is the new ionization constant at 35C  which we want to find H is the enthalpy change of the reaction  assumed to be constant over the temperature range R is the gas constant  8.314 J/molK T1 is the initial temperature in Kelvin  25C + 273.15 = 298.15 K T2 is the final temperature in Kelvin  35C + 273.15 = 308.15 K However, we don't have the value of H. In order to solve this problem, we would need the enthalpy change of the reaction. If you can provide the enthalpy change, we can then calculate the new value of Ka for the weak acid at 35C.