Question

The constant-pressure molar heat capacities of hydrogen and oxygen can be reasonably approximated by 7/2 R, where R is the gas constant. For water in the gas phase, the constant pressure heat capacity is approximately 4R. Estimate the change in standard reaction entropy of the following reaction when the temperature is increased from 273 K to 283 K at constant pressure (that is, calculate ΔSº(283 K)-ΔSº(273 K))

2H₂(g) + O₂(g) → 2H₂O(g)

_______ J/(K.mol)

Answer 1

entropy at 283 K= 2* entropy of H2O- { 2*enropy of H2+1* entropy of O2) at 283K

entropy at 283 = 2* entropy of H2O-(2* entropy of H2+1* entropy of O2) at 273K

entropy change= 2* entropy change of H20 - 2*(entropy change of H2)-1* entropy change of O2

2, 2,1 are coefficients of H2O, H2 and O2 repectively

=2* CpH2O*ln(T2/T1)- 2*CpH2*ln(T2/T1)- 1* CpO2* ln(T2/T1)

=2*4R* ln (283/273) -2*3.5R*ln(283/273)- 3.5R*ln(283/273(

=R*ln(283/273)*( 8-10.5)= - -2.5*8.314 J/mole.K* ln(283/273)=-0.75 J/mole.K