H2O + I2 + As2O3 = HI + As2O5

H_2O water + I_2 iodine + As_2O_3 arsenic trioxide ⟶ HI hydrogen iodide + As_2O_5 arsenic pentoxide

Balance the chemical equation algebraically: H_2O + I_2 + As_2O_3 ⟶ HI + As_2O_5 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2O + c_2 I_2 + c_3 As_2O_3 ⟶ c_4 HI + c_5 As_2O_5 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, I and As: H: | 2 c_1 = c_4 O: | c_1 + 3 c_3 = 5 c_5 I: | 2 c_2 = c_4 As: | 2 c_3 = 2 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 = 2 c_2 = 2 c_3 = 1 c_4 = 4 c_5 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 H_2O + 2 I_2 + As_2O_3 ⟶ 4 HI + As_2O_5

+ + ⟶ +

water + iodine + arsenic trioxide ⟶ hydrogen iodide + arsenic pentoxide

Construct the equilibrium constant, K, expression for: H_2O + I_2 + As_2O_3 ⟶ HI + As_2O_5 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 + 2 I_2 + As_2O_3 ⟶ 4 HI + As_2O_5 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 I_2 | 2 | -2 As_2O_3 | 1 | -1 HI | 4 | 4 As_2O_5 | 1 | 1 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) I_2 | 2 | -2 | ([I2])^(-2) As_2O_3 | 1 | -1 | ([As2O3])^(-1) HI | 4 | 4 | ([HI])^4 As_2O_5 | 1 | 1 | [As2O5] 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) ([I2])^(-2) ([As2O3])^(-1) ([HI])^4 [As2O5] = (([HI])^4 [As2O5])/(([H2O])^2 ([I2])^2 [As2O3])

Construct the rate of reaction expression for: H_2O + I_2 + As_2O_3 ⟶ HI + As_2O_5 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 + 2 I_2 + As_2O_3 ⟶ 4 HI + As_2O_5 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 I_2 | 2 | -2 As_2O_3 | 1 | -1 HI | 4 | 4 As_2O_5 | 1 | 1 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) I_2 | 2 | -2 | -1/2 (Δ[I2])/(Δt) As_2O_3 | 1 | -1 | -(Δ[As2O3])/(Δt) HI | 4 | 4 | 1/4 (Δ[HI])/(Δt) As_2O_5 | 1 | 1 | (Δ[As2O5])/(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) = -1/2 (Δ[I2])/(Δt) = -(Δ[As2O3])/(Δt) = 1/4 (Δ[HI])/(Δt) = (Δ[As2O5])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| water | iodine | arsenic trioxide | hydrogen iodide | arsenic pentoxide formula | H_2O | I_2 | As_2O_3 | HI | As_2O_5 name | water | iodine | arsenic trioxide | hydrogen iodide | arsenic pentoxide IUPAC name | water | molecular iodine | 2, 4, 5-trioxa-1, 3-diarsabicyclo[1.1.1]pentane | hydrogen iodide |

| water | iodine | arsenic trioxide | hydrogen iodide | arsenic pentoxide molar mass | 18.015 g/mol | 253.80894 g/mol | 197.84 g/mol | 127.912 g/mol | 229.84 g/mol phase | liquid (at STP) | solid (at STP) | solid (at STP) | gas (at STP) | solid (at STP) melting point | 0 °C | 113 °C | 312 °C | -50.76 °C | 300 °C boiling point | 99.9839 °C | 184 °C | 465 °C | -35.55 °C | density | 1 g/cm^3 | 4.94 g/cm^3 | 4.15 g/cm^3 | 0.005228 g/cm^3 (at 25 °C) | 4.09 g/cm^3 solubility in water | | | | very soluble | surface tension | 0.0728 N/m | | | | dynamic viscosity | 8.9×10^-4 Pa s (at 25 °C) | 0.00227 Pa s (at 116 °C) | | 0.001321 Pa s (at -39 °C) | odor | odorless | | | |