[umair baloch]

The question is asked to me to complete an assignment and I want to know that what should be written in this answer as I know all the basics of chemical thermodynamics but need to know what should be the answer of the question

[curiouscat]

What's the mathematical formula for enthalpy?

[Schrödinger]

This is got directly from the definition of enthalpy as a thermodynamic parameter.

[umair baloch]

Enthalpy can be defined as:

             H  = E+PV
Change in enthalpy can be  stated as:

             dH  = dE + PdV

Now according to this equation change in enthalpy equals to sum of internal energy plus pressure volume work. This implies that when ever a substance undergoes change in heat contents it is brought by change in internal energy and temperature change keeping pressure constant. For substance like solids and liquids the change in pressure and volume is negligible so we can say that heat change for solids and liquids in a thermodynamic system is equivalent to internal energy changes.

Is this relationship and description applicable? Seniors please check.

[Schrödinger]

Yes. It is fine (for a system under constant pressure ofcourse, since the VdP term should go to 0). And true enough, physical chemists deal with approximately equal values of enthalpy and internal energy due to negligible change in volume of the condensed phases