Why is it difficult to determine the enthalpy change of thermal decomposition of potassium hydrogencarbonate to potassium carbonate?

Answer 1

The reaction which forms potassium hydrogen carbonate from potassium carbonate,

K2CO3 + H2O + CO2 --> KHCO3

is difficult to perform in a laboratory; the same goes for the decomposition.

Hence instead of simply using a calorimeter or similar apparatus, it is necessary to use another reaction route and a Hess Cycle using two reactions such as:

reaction A: K2CO3 + 2HCl --> 2KCL + H2O +CO2

reaction B: KHCO3 + 2HCl --> KCl + H2O +CO2

The enthalpy change of the decomposition of potassium hydrogen carbonate will be twice the enthalpy change for reaction B, minus the enthalpy change for reaction A.

Answer 2

It is difficult to determine the enthalpy change of thermal decomposition of potassium hydrogencarbonate because the reaction is typically very slow under standard conditions, making it hard to measure accurately. Additionally, the reaction may involve simultaneous side reactions, complicating the interpretation of experimental data. The reaction also releases multiple gaseous products, making it challenging to control and measure the enthalpy change accurately.