We’re being asked to determine the **Standard entropy change **for the given reaction:

**2 Mg _{(s)} + O_{2(g}) → 2 MgO_{(s)}**

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

$\overline{){\mathbf{\Delta S}}{{\mathbf{\xb0}}}_{{\mathbf{rxn}}}{\mathbf{=}}{\mathbf{S}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{prod}}{\mathbf{-}}{\mathbf{S}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{react}}}$

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

Calculate the standard entropy change for the reaction

2Mg(s) + O2(g) → 2MgO(s)

using the data from the following table:

Substance | ?H?f (kJ/mol) | ?G?f (kJ/mol) | S? [J/(K?mol)] |

Mg(s) | 0.00 | 0.00 | 32.70 |

O2(g) | 0.00 | 0.00 | 205.0 |

MgO(s) | -602.0 | -569.6 | 27.00 |

Express your answer to four significant figures and include the appropriate units.

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What scientific concept do you need to know in order to solve this problem?

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