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1.
Calculate from the thermal effect Q r of the constant temperature reversible process
For a constant temperature reversible process, the entropy change is equal to the quotient of the heating effect Q r and the temperature T, namely
2.
Obtained from the standard disease SmΘ
If the response is
aA+6B=cC+dD
Then the reaction entropy becomes
which is
[Example 2-8] Find the △ r S m Θ of the reaction 2H 2 (g)+O 2 (g)=2H 2 O(g) at 298K .
A known
3.
Obtained from other thermodynamic data
According to the Gibbs-Holmholtz formula (introduced later in this chapter)
From the free energy change △ r G m Θ and the enthalpy change △ r H m Θ data of the reaction, the entropy change △ r S m Θ can be obtained