Heat of Reaction
The equilibrium constant K is defined by the expression
ln K = -(v3Φ3 + v4Φ4 - v1Φ1 - v2Φ2) |
(3.44) |
Differentiating ln K with respect to T
|
(3.45) |
Let,
|
(3.46) |
Therefore,
|
(3.47) |
Therefore,
|
(3.48) |
where the h's refer to the same temperature T and the same pressure p.
If v1 moles of A1 and v2 moles of A2 combine to form v3 moles of A3 and v4 moles of A4 at constant temperature and pressure, the heat transferred would be, as shown in Fig.3.1, equal to the final enthalpy (v3h3 + v4h4) minus the initial enthalpy (v1h1 + v2h2). This is known as the heat of reaction, and is denoted by ΔH.
Fig.3.1 Heat of Reaction
Hence, heat of reaction is
ΔH = v3h3 + v4h4 - v1h1 + v2h2 |
(3.49) |
Therefore,
|
(3.50) |
This is known as the van’t Hoff equation. This equation can be used to calculate the heat reaction at any desired temperature or within a certain temperature range. By rearranging Eq. (3.50)
