Lecture 2 Flashcards
Give the equation for entropy change of fusion
ΔS= q(Tf)/Tf = ΔH(Tf)/Tf
Define entropy of fusion
increase of entropy when melting a solid substance
Give the equation for entropy change of vaporisation
ΔS= q(Tb)/Tb = ΔH(Tb)/Tb
Define entropy change of vaporisation
increase of entropy
upon vaporisation of a liquid
What is Trouton’s rule?
“ΔvapH / Tb is approximately the same for all liquids, about +85 J K−1 mol−1.” (But there are
exceptions.)
What are the exceptions to troutons rule? Why?
ΔS of water is great than +85JK-1mol-1 due to strong hydrogen bonds between molecules
Why is the ΔS for solid-gas transformations greater?
greatest amount of disorder going solid to gas not via liquid
Why is ΔS for solid-liquid transformations lower?
lower amount of disorder introduced compared to liquid-gas transitions so smaller ΔS
Explain why NH3 is an exception to Trouton’s rule
NH3- has a lone pair of electrons on N so forms hydrogen bonds with other molecules
Give the equation for ΔS for a has expanding isothermally
ΔS= nRln Vf/Vi = nRln Pi/Pf
Give the equation for ΔSm for a perfect gas from Ti to Tf
ΔSm= Cpm ln Tf/Ti
What does Cpm mean?
molar heat capacity of a perfect gas at constant pressure
What does Cvm mean?
molar heat capacity of a perfect gas at constant volume
Give the equation for Cpm for a perfect gas
Cpm= Cvm + R
Give the equations for monoatomic atoms for Cvm and Cpm
Cvm= 3/2R
Cpm= 5/2R
Give the equations for polyatomic atoms for Cvm and Cpm
Cvm> 3/2R
Cpm> 5/2R
What is the entropy of a perfectly crystalline material?
at T=0K entropy is zero
Give the Debye T^3 law
Cvm= aT^3
Sm = 1/3Cvm
at temps very close to zero
Give the equation for residual entropy
N molecules- 2^N orientations
W= 2^N
Sm(0)= klnW
= RlnW
Define the standard molar entropy
the entropy of 1 mol of a substance in its standard state (1 bar pressure)
Units= JK-1mol-1
How can you calculate ΔfusS/ ΔvapS?
ΔS = ΔH/T
How do you calculate absolute molar entropy?
sum of all ΔS values
