Saved Bookmarks
| 1. |
What is enthalpy? |
| Answer» The total heat content of a system at constant pressure is equal to the sum of the internal energy and PV. This is called the enthalpy of a system which is represented by H.Note that enthalpy is also called as heat content.H = U + pvEnthalpy which depends on the three state functions: internal energy, pressure and volume.Hence it is also a state function.Enthalpy of a substance cannot be measured, but change in enthalpy can be measured.Change in enthalpy = Enthalpy of products - Enthalpy of reactants∆H = HP-HRFrom the first law of thermodynamics∆U =qp-P∆Vqp =heat absorbed by the system-P∆V=work done by the system.For finite changes at constant pressure, ∆H= ∆U+∆(PV)∆H=∆U+P∆V (∵ P is constant ) ∆H=qp ∆H=-Ve for exothermic reactions∆H=+Ve for endothermic reactions. | |