H2O + As + NHO3 = NO + H3AsO4

H_2O water + As gray arsenic + HNO_3 nitric acid ⟶ NO nitric oxide + H_3AsO_4 arsenic acid, solid

Balance the chemical equation algebraically: H_2O + As + HNO_3 ⟶ NO + H_3AsO_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2O + c_2 As + c_3 HNO_3 ⟶ c_4 NO + c_5 H_3AsO_4 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, As and N: H: | 2 c_1 + c_3 = 3 c_5 O: | c_1 + 3 c_3 = c_4 + 4 c_5 As: | c_2 = c_5 N: | c_3 = c_4 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 = 3/2 c_3 = 5/2 c_4 = 5/2 c_5 = 3/2 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 2 c_2 = 3 c_3 = 5 c_4 = 5 c_5 = 3 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 H_2O + 3 As + 5 HNO_3 ⟶ 5 NO + 3 H_3AsO_4

+ + ⟶ +

water + gray arsenic + nitric acid ⟶ nitric oxide + arsenic acid, solid

Construct the equilibrium constant, K, expression for: H_2O + As + HNO_3 ⟶ NO + H_3AsO_4 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: 2 H_2O + 3 As + 5 HNO_3 ⟶ 5 NO + 3 H_3AsO_4 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 H_2O | 2 | -2 As | 3 | -3 HNO_3 | 5 | -5 NO | 5 | 5 H_3AsO_4 | 3 | 3 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2O | 2 | -2 | ([H2O])^(-2) As | 3 | -3 | ([As])^(-3) HNO_3 | 5 | -5 | ([HNO3])^(-5) NO | 5 | 5 | ([NO])^5 H_3AsO_4 | 3 | 3 | ([H3AsO4])^3 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 = ([H2O])^(-2) ([As])^(-3) ([HNO3])^(-5) ([NO])^5 ([H3AsO4])^3 = (([NO])^5 ([H3AsO4])^3)/(([H2O])^2 ([As])^3 ([HNO3])^5)

Construct the rate of reaction expression for: H_2O + As + HNO_3 ⟶ NO + H_3AsO_4 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: 2 H_2O + 3 As + 5 HNO_3 ⟶ 5 NO + 3 H_3AsO_4 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 H_2O | 2 | -2 As | 3 | -3 HNO_3 | 5 | -5 NO | 5 | 5 H_3AsO_4 | 3 | 3 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 H_2O | 2 | -2 | -1/2 (Δ[H2O])/(Δt) As | 3 | -3 | -1/3 (Δ[As])/(Δt) HNO_3 | 5 | -5 | -1/5 (Δ[HNO3])/(Δt) NO | 5 | 5 | 1/5 (Δ[NO])/(Δt) H_3AsO_4 | 3 | 3 | 1/3 (Δ[H3AsO4])/(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 = -1/2 (Δ[H2O])/(Δt) = -1/3 (Δ[As])/(Δt) = -1/5 (Δ[HNO3])/(Δt) = 1/5 (Δ[NO])/(Δt) = 1/3 (Δ[H3AsO4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| water | gray arsenic | nitric acid | nitric oxide | arsenic acid, solid formula | H_2O | As | HNO_3 | NO | H_3AsO_4 Hill formula | H_2O | As | HNO_3 | NO | AsH_3O_4 name | water | gray arsenic | nitric acid | nitric oxide | arsenic acid, solid IUPAC name | water | arsenic | nitric acid | nitric oxide | arsoric acid

| water | gray arsenic | nitric acid | nitric oxide | arsenic acid, solid molar mass | 18.015 g/mol | 74.921595 g/mol | 63.012 g/mol | 30.006 g/mol | 141.94 g/mol phase | liquid (at STP) | solid (at STP) | liquid (at STP) | gas (at STP) | solid (at STP) melting point | 0 °C | 817 °C | -41.6 °C | -163.6 °C | 35.5 °C boiling point | 99.9839 °C | 616 °C | 83 °C | -151.7 °C | 160 °C density | 1 g/cm^3 | 5.727 g/cm^3 | 1.5129 g/cm^3 | 0.001226 g/cm^3 (at 25 °C) | 2.2 g/cm^3 solubility in water | | insoluble | miscible | | surface tension | 0.0728 N/m | | | | dynamic viscosity | 8.9×10^-4 Pa s (at 25 °C) | | 7.6×10^-4 Pa s (at 25 °C) | 1.911×10^-5 Pa s (at 25 °C) | odor | odorless | odorless | | |