We can use the following equation to solve for **ΔS˚**** _{rxn}**:

$\overline{){\mathbf{\u2206}\mathbf{S}\mathbf{\xb0}}_{\mathbf{rxn}\mathbf{}}{\mathbf{=}}{\mathbf{}}{\mathbf{S}\mathbf{\xb0}}_{{\mathbf{prod}}}{\mathbf{-}}{\mathbf{S}\mathbf{\xb0}}_{\mathbf{react}\mathbf{}}}$

Note that we need to *multiply each S˚ by the stoichiometric coefficient* since S˚ is in J/mol • K.

The given balanced equation for the reaction is 2 NO(g)+O_{2}(g)→2 NO_{2}(g)

Given:

S° NO_{2}(g) = 240.0 J/(K•mol)

S° O_{2}(g) = 205.2 J/(K•mol)

S° NO(l) = 210.8 J/(K•mol)

Calculate ΔS∘rxn for the reaction 2NO(g)+O_{2}(g)→2NO_{2}(g)

Substance | S∘ (J/mol⋅K) |

NO2 | 240.0 |

O2 | 205.2 |

NO | 210.8 |

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