Question

Measurement of ∆U and ∆H.

Answer 1

Measurement of ∆U and ∆H

• Since, ∆U = q_V

So, ∆U is determined by measuring the heat lost or gained (q_V) for the reaction or process in a closed vessel (constant volume) e.g. Bomb calorimeter.

• ∆H = q_P

In this case, the heat lost or gained (q_p) is determined when the reaction is carried out in an open vessel.

• If reaction involves only solids & liquids or ∆n_g = o, then ∆H = ∆U

• For a cyclic process : ∆U = O, ∆H = O

• During isothermal expansion of an ideal gas, ∆U = O, ∆T = O and ∆H = O.

Thus, it is an isoenthalpic process.