State the first law of thermodynamics (ii) Calculate the enthalpy of combustion of ethylene at 300 K, at constant pressure, If its heat of combustion at constant volume (AU) is -1406 kJ.

State the first law of thermodynamics (ii) Calculate the enthalpy of c

1.	State the first law of thermodynamics (ii) Calculate the enthalpy of combustion of ethylene at 300 K, at constant pressure, If its heat of combustion at constant volume (AU) is -1406 kJ.
Answer» Solution :The first law of thermodynamics states that the dotal energy of an inolated SYSTEM remains constant though it may change from one form to ANOTHER" (or) Energy can neither be created nor destroyed, but may be converted from one form to another (ii) The complete ethylene combustion REACTION can be written as `C_(2)H_(4(g))+3O_(2(g))to2CO_(2(g))+2H_(2)O_((1))` `DeltaU=-140kJ` `Deltan=n_(p(g))-n__(r)(g)` `Delta=2-4=-2` `DeltaH=DeltaU+RTDeltan_(g)` `/_\|=-1406+(8.314xx10^(-3)xx300xx(-2))` `DeltaH=-1410.9kJ`