Saved Bookmarks
| 1. |
Give the relation between DeltaU and DeltaH. |
|
Answer» Solution :(i)When the system at constant pressure undergoes CHANGES from an initial state with `H_1,U_1,V_1` and P parameters to a final state with `H_2,U_2,V_2`and P parameters, the change in enthalpy `DeltaH`, is given by `DeltaH=U+PV` (ii)At initial state `H_1=U_1+PV_1`...(1) (ii)At final state `H_2=U_2+PV_2` ...(2) (2) -(1) `RARR(H_2-H_1) = (U_2-U_1) +P(V_2-V_1)` `DeltaH=DeltaU+PDeltaV` ....(3) Considering `DeltaH=q+w , w=-P DeltaV` `DeltaH=q+w+PDeltaV` `DeltaH=q_P - PDeltaV+ PDeltaV` `DeltaH=q_P` ....(4) `q_P` is the heat absorbed at constant pressure and is CONSIDERED as heat content. (iii) Consider a closed system of gases which are chemically REACTING to produce product gases at constant temperature and pressure with `V_i` and `V_f` as the TOTAL volumes of the reactant and product gases respectively, and `n_i` and `n_f` are the number of moles of gaseous reactants and products . Then , For reactants : `PV_i =n_i RT` For products : `PV_f =n_f RT` Then considering reactants as initial state and products as final state , `P(V_f-V_i)=(n-f-n_i)RT` `PDeltaV=Deltan_g RT` We know `DeltaH=DeltaU+PDeltaV` `therefore DeltaH=DeltaU +Deltan_g RT` ....(5) |
|