I2 + H2S = S + HI

I_2 (iodine) + H_2S (hydrogen sulfide) ⟶ S (mixed sulfur) + HI (hydrogen iodide)

Balance the chemical equation algebraically: I_2 + H_2S ⟶ S + HI Add stoichiometric coefficients, c_i, to the reactants and products: c_1 I_2 + c_2 H_2S ⟶ c_3 S + c_4 HI Set the number of atoms in the reactants equal to the number of atoms in the products for I, H and S: I: | 2 c_1 = c_4 H: | 2 c_2 = c_4 S: | 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_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 1 c_3 = 1 c_4 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | I_2 + H_2S ⟶ S + 2 HI

+ ⟶ +

iodine + hydrogen sulfide ⟶ mixed sulfur + hydrogen iodide

Construct the equilibrium constant, K, expression for: I_2 + H_2S ⟶ S + HI 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: I_2 + H_2S ⟶ S + 2 HI 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 I_2 | 1 | -1 H_2S | 1 | -1 S | 1 | 1 HI | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression I_2 | 1 | -1 | ([I2])^(-1) H_2S | 1 | -1 | ([H2S])^(-1) S | 1 | 1 | [S] HI | 2 | 2 | ([HI])^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 = ([I2])^(-1) ([H2S])^(-1) [S] ([HI])^2 = ([S] ([HI])^2)/([I2] [H2S])

Construct the rate of reaction expression for: I_2 + H_2S ⟶ S + HI 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: I_2 + H_2S ⟶ S + 2 HI 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 I_2 | 1 | -1 H_2S | 1 | -1 S | 1 | 1 HI | 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 I_2 | 1 | -1 | -(Δ[I2])/(Δt) H_2S | 1 | -1 | -(Δ[H2S])/(Δt) S | 1 | 1 | (Δ[S])/(Δt) HI | 2 | 2 | 1/2 (Δ[HI])/(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 = -(Δ[I2])/(Δt) = -(Δ[H2S])/(Δt) = (Δ[S])/(Δt) = 1/2 (Δ[HI])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| iodine | hydrogen sulfide | mixed sulfur | hydrogen iodide formula | I_2 | H_2S | S | HI name | iodine | hydrogen sulfide | mixed sulfur | hydrogen iodide IUPAC name | molecular iodine | hydrogen sulfide | sulfur | hydrogen iodide

| iodine | hydrogen sulfide | mixed sulfur | hydrogen iodide molar mass | 253.80894 g/mol | 34.08 g/mol | 32.06 g/mol | 127.912 g/mol phase | solid (at STP) | gas (at STP) | solid (at STP) | gas (at STP) melting point | 113 °C | -85 °C | 112.8 °C | -50.76 °C boiling point | 184 °C | -60 °C | 444.7 °C | -35.55 °C density | 4.94 g/cm^3 | 0.001393 g/cm^3 (at 25 °C) | 2.07 g/cm^3 | 0.005228 g/cm^3 (at 25 °C) solubility in water | | | | very soluble dynamic viscosity | 0.00227 Pa s (at 116 °C) | 1.239×10^-5 Pa s (at 25 °C) | | 0.001321 Pa s (at -39 °C)