O2 + As = AsO5

O_2 oxygen + As gray arsenic ⟶ AsO5

Balance the chemical equation algebraically: O_2 + As ⟶ AsO5 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 O_2 + c_2 As ⟶ c_3 AsO5 Set the number of atoms in the reactants equal to the number of atoms in the products for O and As: O: | 2 c_1 = 5 c_3 As: | 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_2 = 1 and solve the system of equations for the remaining coefficients: c_1 = 5/2 c_2 = 1 c_3 = 1 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 5 c_2 = 2 c_3 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 5 O_2 + 2 As ⟶ 2 AsO5

+ ⟶ AsO5

oxygen + gray arsenic ⟶ AsO5

Construct the equilibrium constant, K, expression for: O_2 + As ⟶ AsO5 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: 5 O_2 + 2 As ⟶ 2 AsO5 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 | 5 | -5 As | 2 | -2 AsO5 | 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 | 5 | -5 | ([O2])^(-5) As | 2 | -2 | ([As])^(-2) AsO5 | 2 | 2 | ([AsO5])^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])^(-5) ([As])^(-2) ([AsO5])^2 = ([AsO5])^2/(([O2])^5 ([As])^2)

Construct the rate of reaction expression for: O_2 + As ⟶ AsO5 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: 5 O_2 + 2 As ⟶ 2 AsO5 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 | 5 | -5 As | 2 | -2 AsO5 | 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 | 5 | -5 | -1/5 (Δ[O2])/(Δt) As | 2 | -2 | -1/2 (Δ[As])/(Δt) AsO5 | 2 | 2 | 1/2 (Δ[AsO5])/(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 = -1/5 (Δ[O2])/(Δt) = -1/2 (Δ[As])/(Δt) = 1/2 (Δ[AsO5])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| oxygen | gray arsenic | AsO5 formula | O_2 | As | AsO5 name | oxygen | gray arsenic | IUPAC name | molecular oxygen | arsenic |

| oxygen | gray arsenic | AsO5 molar mass | 31.998 g/mol | 74.921595 g/mol | 154.92 g/mol phase | gas (at STP) | solid (at STP) | melting point | -218 °C | 817 °C | boiling point | -183 °C | 616 °C | density | 0.001429 g/cm^3 (at 0 °C) | 5.727 g/cm^3 | solubility in water | | insoluble | surface tension | 0.01347 N/m | | dynamic viscosity | 2.055×10^-5 Pa s (at 25 °C) | | odor | odorless | odorless |