Consider the chemical reaction at 300 K H2 (g) + Cl2 --> HCl(g) ΔH= -185KJ/mole calculate ΔU if 3 mole of H2 completely react with 3 mole of Cl2 (g) to form HCl.

 

                           H₂ (g)+Cl_{2 -->}  HCl(g) ΔH= -185KJ/mole

                                       Δng=0

                                   ΔH= ΔU+ ΔngRT

                                  ΔH= ΔU

                       ΔH_R= -185 KJ/mole ,ΔU_R= -185 KJ/mole

                       H₂ (g)+Cl_{2 -->} HCl(g) ΔH= -185KJ/mole

                         3 mole       3 mole

            Hence           ΔU= -185 X 3 KJ/Mole

What is the relation between change in enthalpy (dH ) and change in internal (dE) for combustion of methan ?

For the given reaction:

                        CH₄(g) + 2O₂(g) ---------> CO₂(g) + 2H₂O(l)

                                          dH = dE + dnRT

                            Dn = no. of mole of products - no. of moles of reactants = 1– 3 = –2

                                             DH = DE – 2RT

1 mole of a real gas is subjected to a process from (2 bar, 40 lit.,300K) to (4 bar, 30 lit., 400 K). If change in internal energy is 35 kJ then calculate enthalpy change for the process.

                       DH = DU + D(PV)

                        D(PV) = P₂V₂ – P₁V₁

                                          = 4 × 30 – 2 × 40

                                   = 40 liter -bar = 4 kJ

                  so      DH = 35 + 4 = 24 kJ

Calculate the work performed when 2 moles of hydrogen expand isothermally and reversibly at 25”C from 15 to 50 litres.

 

A gas absorbs 200J of heat and expands against the external pressure of 1.5 atm from a volume of 0.5 litre to 1.0 litre, Calculate the change in internal energy.