H2SO4 + H2S + K2CrO4 = H2O + K2SO4 + S + K2Cr2O7

H_2SO_4 sulfuric acid + H_2S hydrogen sulfide + K_2CrO_4 potassium chromate ⟶ H_2O water + K_2SO_4 potassium sulfate + S mixed sulfur + K_2Cr_2O_7 potassium dichromate

Balance the chemical equation algebraically: H_2SO_4 + H_2S + K_2CrO_4 ⟶ H_2O + K_2SO_4 + S + K_2Cr_2O_7 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2SO_4 + c_2 H_2S + c_3 K_2CrO_4 ⟶ c_4 H_2O + c_5 K_2SO_4 + c_6 S + c_7 K_2Cr_2O_7 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, S, Cr and K: H: | 2 c_1 + 2 c_2 = 2 c_4 O: | 4 c_1 + 4 c_3 = c_4 + 4 c_5 + 7 c_7 S: | c_1 + c_2 = c_5 + c_6 Cr: | c_3 = 2 c_7 K: | 2 c_3 = 2 c_5 + 2 c_7 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_5 = 1 and solve the system of equations for the remaining coefficients: c_2 = 3 c_1 - 3 c_3 = 2 c_4 = 4 c_1 - 3 c_5 = 1 c_6 = 4 c_1 - 4 c_7 = 1 The resulting system of equations is still underdetermined, so an additional coefficient must be set arbitrarily. Set c_1 = 2 and solve for the remaining coefficients: c_1 = 2 c_2 = 3 c_3 = 2 c_4 = 5 c_5 = 1 c_6 = 4 c_7 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 H_2SO_4 + 3 H_2S + 2 K_2CrO_4 ⟶ 5 H_2O + K_2SO_4 + 4 S + K_2Cr_2O_7

+ + ⟶ + + +

sulfuric acid + hydrogen sulfide + potassium chromate ⟶ water + potassium sulfate + mixed sulfur + potassium dichromate

Construct the equilibrium constant, K, expression for: H_2SO_4 + H_2S + K_2CrO_4 ⟶ H_2O + K_2SO_4 + S + K_2Cr_2O_7 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_2SO_4 + 3 H_2S + 2 K_2CrO_4 ⟶ 5 H_2O + K_2SO_4 + 4 S + K_2Cr_2O_7 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_2SO_4 | 2 | -2 H_2S | 3 | -3 K_2CrO_4 | 2 | -2 H_2O | 5 | 5 K_2SO_4 | 1 | 1 S | 4 | 4 K_2Cr_2O_7 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2SO_4 | 2 | -2 | ([H2SO4])^(-2) H_2S | 3 | -3 | ([H2S])^(-3) K_2CrO_4 | 2 | -2 | ([K2CrO4])^(-2) H_2O | 5 | 5 | ([H2O])^5 K_2SO_4 | 1 | 1 | [K2SO4] S | 4 | 4 | ([S])^4 K_2Cr_2O_7 | 1 | 1 | [K2Cr2O7] 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 = ([H2SO4])^(-2) ([H2S])^(-3) ([K2CrO4])^(-2) ([H2O])^5 [K2SO4] ([S])^4 [K2Cr2O7] = (([H2O])^5 [K2SO4] ([S])^4 [K2Cr2O7])/(([H2SO4])^2 ([H2S])^3 ([K2CrO4])^2)

Construct the rate of reaction expression for: H_2SO_4 + H_2S + K_2CrO_4 ⟶ H_2O + K_2SO_4 + S + K_2Cr_2O_7 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_2SO_4 + 3 H_2S + 2 K_2CrO_4 ⟶ 5 H_2O + K_2SO_4 + 4 S + K_2Cr_2O_7 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_2SO_4 | 2 | -2 H_2S | 3 | -3 K_2CrO_4 | 2 | -2 H_2O | 5 | 5 K_2SO_4 | 1 | 1 S | 4 | 4 K_2Cr_2O_7 | 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_2SO_4 | 2 | -2 | -1/2 (Δ[H2SO4])/(Δt) H_2S | 3 | -3 | -1/3 (Δ[H2S])/(Δt) K_2CrO_4 | 2 | -2 | -1/2 (Δ[K2CrO4])/(Δt) H_2O | 5 | 5 | 1/5 (Δ[H2O])/(Δt) K_2SO_4 | 1 | 1 | (Δ[K2SO4])/(Δt) S | 4 | 4 | 1/4 (Δ[S])/(Δt) K_2Cr_2O_7 | 1 | 1 | (Δ[K2Cr2O7])/(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[H2SO4])/(Δt) = -1/3 (Δ[H2S])/(Δt) = -1/2 (Δ[K2CrO4])/(Δt) = 1/5 (Δ[H2O])/(Δt) = (Δ[K2SO4])/(Δt) = 1/4 (Δ[S])/(Δt) = (Δ[K2Cr2O7])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| sulfuric acid | hydrogen sulfide | potassium chromate | water | potassium sulfate | mixed sulfur | potassium dichromate formula | H_2SO_4 | H_2S | K_2CrO_4 | H_2O | K_2SO_4 | S | K_2Cr_2O_7 Hill formula | H_2O_4S | H_2S | CrK_2O_4 | H_2O | K_2O_4S | S | Cr_2K_2O_7 name | sulfuric acid | hydrogen sulfide | potassium chromate | water | potassium sulfate | mixed sulfur | potassium dichromate IUPAC name | sulfuric acid | hydrogen sulfide | dipotassium dioxido-dioxochromium | water | dipotassium sulfate | sulfur | dipotassium oxido-(oxido-dioxochromio)oxy-dioxochromium

| sulfuric acid | hydrogen sulfide | potassium chromate | water | potassium sulfate | mixed sulfur | potassium dichromate molar mass | 98.07 g/mol | 34.08 g/mol | 194.19 g/mol | 18.015 g/mol | 174.25 g/mol | 32.06 g/mol | 294.18 g/mol phase | liquid (at STP) | gas (at STP) | solid (at STP) | liquid (at STP) | | solid (at STP) | solid (at STP) melting point | 10.371 °C | -85 °C | 971 °C | 0 °C | | 112.8 °C | 398 °C boiling point | 279.6 °C | -60 °C | | 99.9839 °C | | 444.7 °C | density | 1.8305 g/cm^3 | 0.001393 g/cm^3 (at 25 °C) | 2.73 g/cm^3 | 1 g/cm^3 | | 2.07 g/cm^3 | 2.67 g/cm^3 solubility in water | very soluble | | soluble | | soluble | | surface tension | 0.0735 N/m | | | 0.0728 N/m | | | dynamic viscosity | 0.021 Pa s (at 25 °C) | 1.239×10^-5 Pa s (at 25 °C) | | 8.9×10^-4 Pa s (at 25 °C) | | | odor | odorless | | odorless | odorless | | | odorless