HNO3 + As2S3 = H2O + S + NO2 + H3AsO4

HNO_3 (nitric acid) + As_2S_3 (arsenic(III) sulfide) ⟶ H_2O (water) + S (mixed sulfur) + NO_2 (nitrogen dioxide) + H_3AsO_4 (arsenic acid, solid)

Balance the chemical equation algebraically: HNO_3 + As_2S_3 ⟶ H_2O + S + NO_2 + H_3AsO_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HNO_3 + c_2 As_2S_3 ⟶ c_3 H_2O + c_4 S + c_5 NO_2 + c_6 H_3AsO_4 Set the number of atoms in the reactants equal to the number of atoms in the products for H, N, O, As and S: H: | c_1 = 2 c_3 + 3 c_6 N: | c_1 = c_5 O: | 3 c_1 = c_3 + 2 c_5 + 4 c_6 As: | 2 c_2 = c_6 S: | 3 c_2 = 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_2 = 1 and solve the system of equations for the remaining coefficients: c_1 = 10 c_2 = 1 c_3 = 2 c_4 = 3 c_5 = 10 c_6 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 10 HNO_3 + As_2S_3 ⟶ 2 H_2O + 3 S + 10 NO_2 + 2 H_3AsO_4

+ ⟶ + + +

nitric acid + arsenic(III) sulfide ⟶ water + mixed sulfur + nitrogen dioxide + arsenic acid, solid

Construct the equilibrium constant, K, expression for: HNO_3 + As_2S_3 ⟶ H_2O + S + NO_2 + 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: 10 HNO_3 + As_2S_3 ⟶ 2 H_2O + 3 S + 10 NO_2 + 2 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 HNO_3 | 10 | -10 As_2S_3 | 1 | -1 H_2O | 2 | 2 S | 3 | 3 NO_2 | 10 | 10 H_3AsO_4 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HNO_3 | 10 | -10 | ([HNO3])^(-10) As_2S_3 | 1 | -1 | ([As2S3])^(-1) H_2O | 2 | 2 | ([H2O])^2 S | 3 | 3 | ([S])^3 NO_2 | 10 | 10 | ([NO2])^10 H_3AsO_4 | 2 | 2 | ([H3AsO4])^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 = ([HNO3])^(-10) ([As2S3])^(-1) ([H2O])^2 ([S])^3 ([NO2])^10 ([H3AsO4])^2 = (([H2O])^2 ([S])^3 ([NO2])^10 ([H3AsO4])^2)/(([HNO3])^10 [As2S3])

Construct the rate of reaction expression for: HNO_3 + As_2S_3 ⟶ H_2O + S + NO_2 + 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: 10 HNO_3 + As_2S_3 ⟶ 2 H_2O + 3 S + 10 NO_2 + 2 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 HNO_3 | 10 | -10 As_2S_3 | 1 | -1 H_2O | 2 | 2 S | 3 | 3 NO_2 | 10 | 10 H_3AsO_4 | 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 HNO_3 | 10 | -10 | -1/10 (Δ[HNO3])/(Δt) As_2S_3 | 1 | -1 | -(Δ[As2S3])/(Δt) H_2O | 2 | 2 | 1/2 (Δ[H2O])/(Δt) S | 3 | 3 | 1/3 (Δ[S])/(Δt) NO_2 | 10 | 10 | 1/10 (Δ[NO2])/(Δt) H_3AsO_4 | 2 | 2 | 1/2 (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 = -1/10 (Δ[HNO3])/(Δt) = -(Δ[As2S3])/(Δt) = 1/2 (Δ[H2O])/(Δt) = 1/3 (Δ[S])/(Δt) = 1/10 (Δ[NO2])/(Δt) = 1/2 (Δ[H3AsO4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| nitric acid | arsenic(III) sulfide | water | mixed sulfur | nitrogen dioxide | arsenic acid, solid formula | HNO_3 | As_2S_3 | H_2O | S | NO_2 | H_3AsO_4 Hill formula | HNO_3 | As_2S_3 | H_2O | S | NO_2 | AsH_3O_4 name | nitric acid | arsenic(III) sulfide | water | mixed sulfur | nitrogen dioxide | arsenic acid, solid IUPAC name | nitric acid | | water | sulfur | Nitrogen dioxide | arsoric acid

| nitric acid | arsenic(III) sulfide | water | mixed sulfur | nitrogen dioxide | arsenic acid, solid molar mass | 63.012 g/mol | 246 g/mol | 18.015 g/mol | 32.06 g/mol | 46.005 g/mol | 141.94 g/mol phase | liquid (at STP) | solid (at STP) | liquid (at STP) | solid (at STP) | gas (at STP) | solid (at STP) melting point | -41.6 °C | 300 °C | 0 °C | 112.8 °C | -11 °C | 35.5 °C boiling point | 83 °C | | 99.9839 °C | 444.7 °C | 21 °C | 160 °C density | 1.5129 g/cm^3 | 3.43 g/cm^3 | 1 g/cm^3 | 2.07 g/cm^3 | 0.00188 g/cm^3 (at 25 °C) | 2.2 g/cm^3 solubility in water | miscible | | | | reacts | surface tension | | | 0.0728 N/m | | | dynamic viscosity | 7.6×10^-4 Pa s (at 25 °C) | | 8.9×10^-4 Pa s (at 25 °C) | | 4.02×10^-4 Pa s (at 25 °C) | odor | | | odorless | | |