Question

Suppose that 145 g of ethanol at 20◦C is mixed

with 235 g of ethanol at 84 ◦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:

∆Ssys = 392.73-179.62 =213.11  J/K.

Explanation:

m_1=145,T_1=20°C

and

m_2=235,  T_2=84 °C

let, specific heat capacity be c(small)=2.42 J/g/K

let,

the constant temperature obtained after mixing is t

so heat absorbed(1st portion of ethanol),$Q_1=m_1c(T-T_1)$

heat  heat lost(2nd portion of ethanol), ,$Q_2=m_2c(T_2-T)$

Now, heat lost= heat gained

,$m_1c(T-T_1)$= $m_2c(T_2-T)$

$145(T-20)$= $235(84-T)$

T=61.25°C

$\Delta S_1= cm_1ln(\frac{T}{T_1} )$

putting values we get

$\Delta S_1= 2.42\times145ln(\frac{61.25}{20} )$

ΔS_1= 392.73 J/ K.

and

$\Delta S_2= 2.42\times235ln(\frac{61.25}{84} )$

ΔS_2= -179.62557  J/K.

∆Ssys = 392.73-179.62 =213.11  J/K.