Question

Which enthalpy is always positive?

Answer 1

1. Enthalpy is a thermodynamic entity that is used for systems and surroundings.
2. Enthalpy is related to the heat content of the system and is defined as the sum of internal energy with the product of pressure and volume.
3. Enthalpy can be mathematically represented as follows:
   $\mathrm{H}=\mathrm{U}+\mathrm{pv}$
4. Therefore the change in enthalpy can be represented as:
   $∆\mathrm{H}=∆\mathrm{U}+\mathrm{P}∆\mathrm{V}$; where$∆\mathrm{H}$ is the change in enthalpy,$∆\mathrm{U}$ is the change in the internal energy, p is the pressure, $∆\mathrm{V}$ is the change in volume.
5. In endothermic reactions, the heat or energy is supplied to the chemical reaction to occur.
6. The reaction in which the reactants form the product in a forwarding direction always gives positive enthalpy.
7. Example:
   $$\begin{gathered} {\mathrm{NH}}_4{\mathrm{NO}}_3\left(\mathrm{s}\right)\to {\mathrm{NH}}_4^{+}\left(\mathrm{s}\right)+{\mathrm{NO}}_3^{-}\left(\mathrm{l}\right)∆\mathrm{H}=+\mathrm{x} \\ \mathrm{Ammonium}\mathrm{Ammonium}\mathrm{Nitrate} \\ \mathrm{nitrate}\mathrm{ion}\mathrm{ion} \end{gathered}$$
8. The $∆\mathrm{H}=+\mathrm{x}$ denotes the enthalpy which is always positive in nature.