Chemistry - Thermochemistry Question with Solution | TestHub
Volumes of 50 ml of 1 M-NaOH and 50 ml of 1 M-HCl both at the same temperature were mixed in a calorimeter of very small heat capacity. A temperature rise of 4.11 K was recorded. In a second experiment, the HCl was replaced by 50 ml of 1 M-HCOOH. The temperature rise was 3.21 K. The enthalpy of ionization (in kcal/mol) of HCOOH is
Answer:
Solution:
Given the same experimental setup, the heat evolved per mole is directly proportional to the change in temperature, Δ T.
For a strong acid, the enthalpy of neutralization, Δ Hneut, is -13.7 kcal/mol.
For formic acid (HCOOH), a weak acid, the observed enthalpy of neutralization is calculated as:
Δ Hneut = -13.7 × 3.21/4.11 = -10.7 kcal/mol
The difference in enthalpy is due to the ionization of the weak acid, which absorbs energy. The enthalpy of ionization, Δ Hion, is:
Δ Hion = -10.7 - (-13.7) = +3.0 kcal/mol
The magnitude of the enthalpy of ionization is 3 kcal/mol. Therefore, the answer is 3.
