O2 + Mg = MgO

O_2 (oxygen) + Mg (magnesium) ⟶ MgO (magnesium oxide)

Balance the chemical equation algebraically: O_2 + Mg ⟶ MgO Add stoichiometric coefficients, c_i, to the reactants and products: c_1 O_2 + c_2 Mg ⟶ c_3 MgO Set the number of atoms in the reactants equal to the number of atoms in the products for O and Mg: O: | 2 c_1 = c_3 Mg: | c_2 = c_3 Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 2 c_3 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | O_2 + 2 Mg ⟶ 2 MgO

+ ⟶

oxygen + magnesium ⟶ magnesium oxide

| oxygen | magnesium | magnesium oxide molecular enthalpy | 0 kJ/mol | 0 kJ/mol | -601.6 kJ/mol total enthalpy | 0 kJ/mol | 0 kJ/mol | -1203 kJ/mol | H_initial = 0 kJ/mol | | H_final = -1203 kJ/mol ΔH_rxn^0 | -1203 kJ/mol - 0 kJ/mol = -1203 kJ/mol (exothermic) | |

| oxygen | magnesium | magnesium oxide molecular entropy | 205 J/(mol K) | 33 J/(mol K) | 27 J/(mol K) total entropy | 205 J/(mol K) | 66 J/(mol K) | 54 J/(mol K) | S_initial = 271 J/(mol K) | | S_final = 54 J/(mol K) ΔS_rxn^0 | 54 J/(mol K) - 271 J/(mol K) = -217 J/(mol K) (exoentropic) | |

Construct the equilibrium constant, K, expression for: O_2 + Mg ⟶ MgO Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the activity expression for each chemical species. • Use the activity expressions to build the equilibrium constant expression. Write the balanced chemical equation: O_2 + 2 Mg ⟶ 2 MgO Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i O_2 | 1 | -1 Mg | 2 | -2 MgO | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression O_2 | 1 | -1 | ([O2])^(-1) Mg | 2 | -2 | ([Mg])^(-2) MgO | 2 | 2 | ([MgO])^2 The equilibrium constant symbol in the concentration basis is: K_c Mulitply the activity expressions to arrive at the K_c expression: Answer: | | K_c = ([O2])^(-1) ([Mg])^(-2) ([MgO])^2 = ([MgO])^2/([O2] ([Mg])^2)

Construct the rate of reaction expression for: O_2 + Mg ⟶ MgO Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the rate term for each chemical species. • Write the rate of reaction expression. Write the balanced chemical equation: O_2 + 2 Mg ⟶ 2 MgO Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i O_2 | 1 | -1 Mg | 2 | -2 MgO | 2 | 2 The rate term for each chemical species, B_i, is 1/ν_i(Δ[B_i])/(Δt) where [B_i] is the amount concentration and t is time: chemical species | c_i | ν_i | rate term O_2 | 1 | -1 | -(Δ[O2])/(Δt) Mg | 2 | -2 | -1/2 (Δ[Mg])/(Δt) MgO | 2 | 2 | 1/2 (Δ[MgO])/(Δt) (for infinitesimal rate of change, replace Δ with d) Set the rate terms equal to each other to arrive at the rate expression: Answer: | | rate = -(Δ[O2])/(Δt) = -1/2 (Δ[Mg])/(Δt) = 1/2 (Δ[MgO])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| oxygen | magnesium | magnesium oxide formula | O_2 | Mg | MgO name | oxygen | magnesium | magnesium oxide IUPAC name | molecular oxygen | magnesium | oxomagnesium

| oxygen | magnesium | magnesium oxide molar mass | 31.998 g/mol | 24.305 g/mol | 40.304 g/mol phase | gas (at STP) | solid (at STP) | solid (at STP) melting point | -218 °C | 648 °C | 2852 °C boiling point | -183 °C | 1090 °C | 3600 °C density | 0.001429 g/cm^3 (at 0 °C) | 1.738 g/cm^3 | 3.58 g/cm^3 solubility in water | | reacts | surface tension | 0.01347 N/m | | dynamic viscosity | 2.055×10^-5 Pa s (at 25 °C) | | odor | odorless | | odorless