Question

Which of the following is /are correct?
A.$\Delta H = \Delta U + \Delta \left( {PV} \right)$ when P and V both changes
B. $\Delta H = \Delta U + P\Delta V$when pressure is constant
C. $\Delta H = \Delta U + V\Delta P$when volume is constant
D. All are correct

Answer 1

Hint: Thermodynamic is the study of heat absorbed or given off during the course of a chemical reaction. Some of the thermodynamic quantities are enthalpy, entropy, internal energy etc.

Complete step by step answer:
-Internal energy is the exchange of energy between the surrounding and system at constant volume.
- However, most of the physical process and chemical reactions are carried in open tubes. As they are exposed to atmosphere directly, they are under atmospheric pressure directly which is constant for a particular place, that is, the laboratory.
- But the volume does not remain constant because the reaction results either increase or decrease of volume. If the volume increases, work is done by the system and decrease of internal energy takes place.
-Similarly, if the decrease of volume occurs, work is done on the system which results in increases of internal energy. So, we can conclude that energy change in a reaction at constant temperature and pressure does not depend only on change of internal energy but also on the expansion and contraction. So, the term enthalpy is introduced. The enthalpy depicts the heat content.
When pressure is constant,
$\Delta H = \Delta U + P\Delta V$
Here, $\Delta H$ represents change in enthalpy, $\Delta U$ is change in internal energy, P is pressure and V is volume

Hence, the correct option is B.

Note:
Both internal energy and enthalpy are state functions. State function is a property of a system that depends on the state of the system.