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 find the change in entropy of the universe (ΔSuniv) for this phase change, you can use the equation ΔSuniv = ΔSsys + ΔSsurr.
Given that ΔSsys (change in entropy of the system) is +79.0 J/K, we need to calculate the ΔSsurr (change in entropy of the surroundings) and add it to ΔSsys to find ΔSuniv.
For the phase change from liquid (C7H16(l)) to gas (C7H16(g)), we can assume that the surroundings are at a constant temperature of 25°C (298 K).
To calculate ΔSsurr, we can use the equation ΔSsurr = -ΔH/T, where ΔH is the enthalpy change and T is the temperature in Kelvin.
Given that ΔHvap (enthalpy change of vaporization) for heptane is +21.6 kJ/mol, we need to convert it to J/mol by multiplying it by 1000.
ΔHvap = +21.6 kJ/mol = +21.6 × 1000 J/mol = +21,600 J/mol
Now we can calculate ΔSsurr:
ΔSsurr = -ΔHvap / T = -21,600 J/mol / 298 K
Calculating ΔSsurr gives you a negative value, as the reaction is exothermic (heat is released to the surroundings), which means ΔSsurr is -72.48 J/K.
Now, you can find ΔSuniv:
ΔSuniv = ΔSsys + ΔSsurr = 79.0 J/K + (-72.48 J/K)
Calculating ΔSuniv for this phase change gives you a value of +6.52 J/K.
Therefore, the change in entropy of the universe (ΔSuniv) for this phase change is +6.52 J/K.