Heat of Solution and Mixing
• Binary solutions or mixture
• ideal mixture :
o The total properties of the stream
are the appropriate weighted sum
• gas-gas
of the properties of the individual
• gas-solid
components.
• solid-solid
෡𝑚𝑖𝑥𝑡𝑢𝑟𝑒 = 𝑥𝐴 ∆𝐻
෡𝐴 + 𝑥𝐵 ∆𝐻
෡𝐵 + 𝑥𝐶 ∆𝐻
෡𝐶 +…
∆𝐻
o We can ignore the energy changes
that occur on mixing
• Real mixture
• gas-liquid
• liquid-liquid
• solid-liquid
(heat of solution)
(heat of mixing)
(heat of solution)
෡ 𝒐𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
∆𝑯
෡ 𝒐𝒇,𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 = ∆𝑯
෡ 𝒐𝒇,𝒔𝒐𝒍𝒖𝒕𝒆 +∆𝑯
෡ 𝒐𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
∆𝑯
෡ 𝒐𝒅𝒊𝒍𝒍𝒖𝒕𝒊𝒐𝒏
∆𝑯
෡ 𝒐𝒇,𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
∆𝑯
෡ 𝒐𝒇,𝒔𝒐𝒍𝒖𝒕𝒆
∆𝑯
Heat formation of solution is the the hat of formation of the solution itself
per mol of HCl. It is important to remember that the heat of formation of
the H2O does not enter into the calculation. It is defined as zero for the
process of solution.
Example28.2 Application of Heat of
Solution Data
Hydrochloric acid is an important industrial
chemical. To make aqueous solutions of it in
a commercial grade (known as muriatic
acid), purified HCl(g) is absorbed in water in
a tantalum absorber in a steady state
continuous process. How much heat must
be removed from the absorber by the
cooling water per 100 kg of product if hot
HCl(g) at 120 oC is fed into water in the
absorber as shown in Figure E28.2? The
feed water can be assumed to be at 25 oC,
and the exit product HCl(aq) is 25% HCl (by
weight) at 35 oC. The cooling water does not
mix with the HCl solution.
Q
<2> H2O (l) 25 oC
Absorber
<1> HCl (g) 120 oC
<3> HCl solution 35 oC
HCl solution 25% weight
Component
MW
mass frac.
HCl
36.5
0.25
H2O
18
0.75
HCl solution
20.612
[J/mol HCl]
mass
mol
mol frac. composition DHosolution
25000 684.932
0.141
1
75000 4166.667
0.859
6.083
-65378.192
100000 4851.598
7.083
<2> H2O (l) 25 oC
Q
<1> HCl (g) 120 oC
Absorber
<3> HCl solution 35 oC
Tref. =
Component
HCl
H2O
HCl solution
total
25
MW
36.5
18
20.612
Cp [J/(mol.C)]
A
B
29.13
-0.00124
55.652
DHof
[J/mol]
DHosolution mass frac.
1
0
-9229.862
0
T=
120
<1>
mol
684.932
0
0
684.932
mass
H
25000 1889596
0
0
0
0
25000 1889596
<2> H2O (l) 25 oC
Q
<1> HCl (g) 120 oC
Absorber
<3> HCl solution 35 oC
T=
25
<2>
mass frac. mol
0
0
1
4166.667
0
0
1 4166.667
mass
0
75000
0
75000
T=
<Solution>
mol
H
H
0
0
0
4851.598
0
<3>
mass frac. mol
0
0
0
0
44779583.53
1
4851.598
44779583.53
1 4851.598
35
Q
mass
H
0
0
0
0
100000 2700000
100000 2700000 43969179