Calculate the S(univ) for the following phase change at 25 deg celcius. The boiling point of heptane is 98.0 Celcius and has a Delta Hvap= +21.6kj/mol.
C7H16(l)--> C7H16(g) Delta S= +79.0j/k
I know that the equation is
Delta Suniv= DSsys + DSsurr
but for DSurr= -0.216J/371k= 5.82*10^-4
But idk how to get Dsys...
Please explain it to me thoroughly!!!
dSsys = dH/T
I think you should look at your dH value. Isn't 21.6 kJ/mol = 21600 J/mol
So since
Delta S= +79.0J/K
is Delta S equal to Delta Ssys?
I don't get the relationship of Delta S and sys and surr with delta S (entropy)
that would make it become +79.0J/K DSsys
and then DSurrs= (-21600J/mol*1mol)/298K= -72.5J/K
Suniv= +79.0J/K+-72.5J/K= +6.5
DrBob222
Yes, dS for the system is 79.0 J/K*mol but I would use T at boiling point of 98C (371K) to solve for this because you're using dHvap and it makes sense to use T at the vapor point.
I note the problem asks for dSuniv at 298. I think you can get that by
dG = -dH/T = (dSuniv) = -RT*lnK using 371 for T and solve for K @ 371 kelvin; then
dG = dGo + RTlnK using T = 298 and K from above and solve for dGo.
I did as you said and I got the wrong answer. the correct asnwer is supposed to be +6.5, and I am getting -25.8..
Can you just show me how to do it with numbers and steps. I am just more confused now.
Could I just use the formula
DSuniv= DSsys- (DHsys/T)
79.0J/K- 21600/298k= +6.5
Calculate the S(univ) for the following phase change at 25 deg celcius. The boiling point of heptane is 98.0 Celcius and has a Delta Hvap= +21.6kj/mol.
C7H16(l)--> C7H16(g) Delta S= +79.0j/k
I know that the equation is
Delta Suniv= DSsys + DSsurr
PLEASE SOMEONE HELP ME WITH THIS PROBLEM, I CANT FIGURE IT OUT!!!
All I know is Delta Ssys= +79.0
To calculate the change in entropy of the system (DSsys) for the given phase change, we can use the equation:
DSsys = DSprod - DSreact
where DSprod is the entropy of the products and DSreact is the entropy of the reactants.
In this case, the reactant is heptane in liquid form (C7H16(l)), and the product is heptane in gaseous form (C7H16(g)). The given entropy change for this phase change is DS = +79.0 J/K.
Since there is no other information provided about the entropy of heptane in both liquid and gas phases, we can assume that there is no change in entropy for the reactant and product. Therefore:
DSsys = DSprod - DSreact = 0 - (79.0 J/K) = -79.0 J/K
Now that we have the value for DSsys, we can calculate DSuniv (the change in total entropy of the universe) using the equation:
DSuniv = DSsys + DSsurr
where DSsurr is the change in entropy of the surroundings.
You mentioned that DSsurr = -0.216 J/371 K = 5.82 x 10^-4 J/K. However, the value for DSsurr seems to be incorrect based on the given data.
Assuming a correct value for DSsurr, you can substitute the known values into the equation to calculate DSuniv:
DSuniv = (-79.0 J/K) + (5.82 x 10^-4 J/K) = -78.9994 J/K
Note that the change in entropy of the universe, DSuniv, is negative in this case, indicating a decrease in overall disorder.