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 SHOW ME HOW TO DO IT! I am confused unless I can see it done. I want to understand it by seeing it done cause I don't get written steps. I'm a more visual learner.
To calculate the S(univ) for the given phase change, we need to find the change in entropy for the system (DSsys) and the surroundings (DSsurr), and then add them together.
1. Start by calculating the change in entropy for the system (DSsys):
DSsys = DS(products) - DS(reactants)
For a phase change, DSsys can be determined using the equation:
DSsys = Delta Hvap / T
where Delta Hvap is the enthalpy of vaporization and T is the temperature in Kelvin (25°C + 273.15 = 298.15 K).
Plugging in the values:
DSsys = 21.6 kJ/mol / 298.15 K
Note: The units of Delta Hvap must be consistent with the units of R (the gas constant) in order to obtain the correct units for entropy (J/mol·K). If Delta Hvap is given in kJ, as in this case, it needs to be converted to J by multiplying it by 1000.
2. Next, calculate the change in entropy for the surroundings (DSsurr):
DSsurr = -DS(sys) = -Delta Hvap / T
Note that DSsurr has the opposite sign of DSsys because the process is exothermic (heat is released to the surroundings).
Plugging in the values:
DSsurr = -21.6 kJ/mol / 298.15 K
Again, conversion is necessary to maintain consistent units.
3. Finally, calculate the S(univ) by adding the DSsys and DSsurr:
DSsys = 21.6 kJ/mol / 298.15 K
DSsurr = -21.6 kJ/mol / 298.15 K
S(univ) = DSsys + DSsurr
Note that Delta S, DSsys, and DSsurr all have the units of J/mol·K.
By performing the calculations, you will obtain the value of S(univ) for the given phase change at 25°C.