文档介绍：Chapter 5
Standard Thermodynamic Functions of Reaction
Chapter 5
Physical Chemistry
Standard States of Pure Substances
Standard state P = 1 bar
Gas: P = 1 bar, T, gas ideal
The standard-state pressure is denoted by Po:
Po 1 bar, T
Solid or liquid:P = 1 bar, T
The standard state of a substance at a specified temperature is its pure form at 1 bar.
Standard Thermodynamic Functions of Reaction
Physical Chemistry
Chapter 5
Standard Enthalpy of Reaction
For a chemical reaction
Then
aA + bB cC + dD
Molar enthalpy of substance (C) in standard state at T
Standard enthalpy (change) of reaction
(Sometime, is used for )
For the general reaction (Eq. ())
()*
Physical Chemistry
Chapter 5
Standard Enthalpy of Reaction
For example
Then
Ho depends on how the reaction is written
2 C6H6 (l) + 15 O2 (g) 12 CO2 (g) + 6 H2O (l)
C6H6 (l) + O2 (g) 6 CO2 (g) + 3 H2O (l)
Physical Chemistry
Chapter 5
Standard Enthalpy of Formation
The reference form (reference phase) of an element at T is usually taken as the form of the element that is most stable at T and 1-bar pressure.
For example, for H2CO(g) at 307 K
C (graphite, 307 K, Po )+H2 (ideal gas, 307 K, Po)+½O2 (ideal gas, 307 K, Po ) H2CO (ideal gas, 307 K, Po)
For an element in its reference form, is zero.
For example, =0。
C (graphite, 307 K, Po ) C (diamond, 307 K, Po)
C (graphite, 307 K, Po ) C (graphite, 307 K, Po)
Nothing happens in this “process”
however, ( )
Physical Chemistry
Chapter 5
Consider the reaction
aA+b B → cC+dD
The standard enthalpy change for a chemical reaction
()*
Reactants aA + bB
in their standard states at T
+ dD
in their standard states at T
Elements
in their standard states at T
(1)
(2)
(3)
Fig.
Physical Chemistry
Chapter 5
a A+b B →c C+d D
+)
Reactants aA + bB
in their standard states at T
+ dD
in their standard states at T
Elements
in their standard states at T
(1)
(2)
(3)
Fig.
Physical Chemistry
Chapter 5
Determ