Question

Suppose that 125 g of ethanol at 22◦C is mixed
with 250 g of ethanol at 89 ◦C at constant
atmospheric pressure in a thermally insulated
vessel. What is the �Ssys for the process?
The specific heat capacity for ethanol is 2.42
J/g K.

Answer 1

First, calculate the final temperature of the system; i.e., Tfinal this way.
[mass warm ethanol x sp.h. ethanol x (Tfinal-Tinitial)] + [mass cooler ethanol x sp.h. ethanol x (Tfinal - Tinitial)] = 0
Calculate Tfinal. Then use Tfinal for the next two calculations to give Qwarmer ethanol and Qcooler ethanol
Qwarmer = 250 g x 2.42 J/g*K x (Tfinal - 89) = ? J
Qcooler = 125 g x 2.42 J/g*K x (Tfinal - 22) = ? J
Calculate dSwarmer = Qwarmer/Tavg where Tavg is the avg T for Tfinal and Tinitial for the warmer. Be sure Tavg is in Kelvin Do same for dScooler = Qcooler/Tavg where Tavg is the avg for the cooler ethanol.
Then dSsystem at equillibrium will be
dSsystem = dSwarmer + dScooler. One will be negative and one will be positive.
Post your work if you get stuck.