S + HI = I2 + H2S

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

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

+ ⟶ +

mixed sulfur + hydrogen iodide ⟶ iodine + hydrogen sulfide

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

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

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

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