H2O + Cl2 + As2O3 = HCl + H3AsO4

H_2O water + Cl_2 chlorine + As_2O_3 arsenic trioxide ⟶ HCl hydrogen chloride + H_3AsO_4 arsenic acid, solid

Balance the chemical equation algebraically: H_2O + Cl_2 + As_2O_3 ⟶ HCl + H_3AsO_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2O + c_2 Cl_2 + c_3 As_2O_3 ⟶ c_4 HCl + 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, Cl and As: H: | 2 c_1 = c_4 + 3 c_5 O: | c_1 + 3 c_3 = 4 c_5 Cl: | 2 c_2 = c_4 As: | 2 c_3 = c_5 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_3 = 1 and solve the system of equations for the remaining coefficients: c_1 = 5 c_2 = 2 c_3 = 1 c_4 = 4 c_5 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 5 H_2O + 2 Cl_2 + As_2O_3 ⟶ 4 HCl + 2 H_3AsO_4

+ + ⟶ +

water + chlorine + arsenic trioxide ⟶ hydrogen chloride + arsenic acid, solid

Construct the equilibrium constant, K, expression for: H_2O + Cl_2 + As_2O_3 ⟶ HCl + 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: 5 H_2O + 2 Cl_2 + As_2O_3 ⟶ 4 HCl + 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 H_2O | 5 | -5 Cl_2 | 2 | -2 As_2O_3 | 1 | -1 HCl | 4 | 4 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 H_2O | 5 | -5 | ([H2O])^(-5) Cl_2 | 2 | -2 | ([Cl2])^(-2) As_2O_3 | 1 | -1 | ([As2O3])^(-1) HCl | 4 | 4 | ([HCl])^4 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 = ([H2O])^(-5) ([Cl2])^(-2) ([As2O3])^(-1) ([HCl])^4 ([H3AsO4])^2 = (([HCl])^4 ([H3AsO4])^2)/(([H2O])^5 ([Cl2])^2 [As2O3])

Construct the rate of reaction expression for: H_2O + Cl_2 + As_2O_3 ⟶ HCl + 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: 5 H_2O + 2 Cl_2 + As_2O_3 ⟶ 4 HCl + 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 H_2O | 5 | -5 Cl_2 | 2 | -2 As_2O_3 | 1 | -1 HCl | 4 | 4 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 H_2O | 5 | -5 | -1/5 (Δ[H2O])/(Δt) Cl_2 | 2 | -2 | -1/2 (Δ[Cl2])/(Δt) As_2O_3 | 1 | -1 | -(Δ[As2O3])/(Δt) HCl | 4 | 4 | 1/4 (Δ[HCl])/(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 = -1/5 (Δ[H2O])/(Δt) = -1/2 (Δ[Cl2])/(Δt) = -(Δ[As2O3])/(Δt) = 1/4 (Δ[HCl])/(Δt) = 1/2 (Δ[H3AsO4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| water | chlorine | arsenic trioxide | hydrogen chloride | arsenic acid, solid formula | H_2O | Cl_2 | As_2O_3 | HCl | H_3AsO_4 Hill formula | H_2O | Cl_2 | As_2O_3 | ClH | AsH_3O_4 name | water | chlorine | arsenic trioxide | hydrogen chloride | arsenic acid, solid IUPAC name | water | molecular chlorine | 2, 4, 5-trioxa-1, 3-diarsabicyclo[1.1.1]pentane | hydrogen chloride | arsoric acid

| water | chlorine | arsenic trioxide | hydrogen chloride | arsenic acid, solid molar mass | 18.015 g/mol | 70.9 g/mol | 197.84 g/mol | 36.46 g/mol | 141.94 g/mol phase | liquid (at STP) | gas (at STP) | solid (at STP) | gas (at STP) | solid (at STP) melting point | 0 °C | -101 °C | 312 °C | -114.17 °C | 35.5 °C boiling point | 99.9839 °C | -34 °C | 465 °C | -85 °C | 160 °C density | 1 g/cm^3 | 0.003214 g/cm^3 (at 0 °C) | 4.15 g/cm^3 | 0.00149 g/cm^3 (at 25 °C) | 2.2 g/cm^3 solubility in water | | | | miscible | surface tension | 0.0728 N/m | | | | dynamic viscosity | 8.9×10^-4 Pa s (at 25 °C) | | | | odor | odorless | | | |