To calculate the entropy change ∆S for the reaction, we first need to write the balanced chemical equation for the reaction between hydrogen gas H2 and oxygen gas O2 :
2H2 g + O2 g → 2H2O g
Next, we need to find the standard molar entropy value for water vapor H2O . The standard molar entropy value for H2O g is 188.8 J/K•mol.
Now we can calculate the entropy change ∆S for the reaction using the following formula:
∆S = ∑nS products - ∑nS reactants
where n is the number of moles and S is the standard molar entropy value.
For the reactants, we have:
2 moles H2 × 130.7 J/K•mol + 1 mole O2 × 205.0 J/K•mol = 261.4 J/K + 205.0 J/K = 466.4 J/K
For the products, we have:
2 moles H2O × 188.8 J/K•mol = 377.6 J/K
Now we can calculate the entropy change ∆S :
∆S = 377.6 J/K - 466.4 J/K = -88.8 J/K
The entropy change for the reaction between 2.0 moles of hydrogen gas H2 and 1.0 mole of oxygen gas O2 at constant pressure and a temperature of 298 K is -88.8 J/K.