Question

Correct mathematical formulation of first law of thermodynamics used in thermochemistry is :

• A. $\Delta H=\Delta U+\Delta nRT$
• B. $\Delta U=\Delta H+\Delta nRT$
• C. $\Delta H=\Delta U-\Delta nRT$
• D. $\Delta H=-\Delta U+\Delta nRT$

Answer 1

The correct option is A $\Delta H=\Delta U+\Delta nRT$

The First Law of Thermodynamics states that energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed, under any circumstances. Mathematically, this is represented as

$\Delta H=\Delta U+\Delta nRT$

with,

$\Delta H$ is the heat exchanged between a system and its surroundings,

$\Delta U$ is the total change in internal energy of a system,

$\Delta nRT$ is the work done by or on the system.