Question

Suppose that 140 g of ethanol at 29◦C ismixed
with 275 g of ethanol at 87 ◦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 in units of J/K.​

Answer 1

Answer:

m1=140 g T1=302.15 K m2=275 g T2=360.15 K c=2.42J/g K

First find Tf after mixing ethanol

$Q_{cold} =Q_{hot}$

$m_{1} *C*ΔT_{cold} =m_{2} *C*ΔT_{hot}$

$m_{1} *ΔT_{cold} =m_{2}* ΔT_{hot}$

$m_{1} (T_{f} -T_{1} )=m_{2} (T_{2} -T_{f} )$

$(140)(T_{f} -302.15)=275(360.15-T_{f} )$

$140T_{f-} 42301=99041.25-275T_{f}$

$415T_{f} =141342.25$

$T_{f} =340.58K$

Next entropy change of system

ΔS=ΔS1+ΔS2

ΔS=m1*C*ln(Tf/T1)+m2*C*ln(Tf/T2)

ΔS=(140)*(2.42)*ln[340.58/302.15]+(275)*(2.42)*ln[340.58/360.15]

ΔS=40.506-37.182

ΔS=3.324J/K