H2S + K = H2 + K2S

H_2S hydrogen sulfide + K potassium ⟶ H_2 hydrogen + K2S

Balance the chemical equation algebraically: H_2S + K ⟶ H_2 + K2S Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2S + c_2 K ⟶ c_3 H_2 + c_4 K2S Set the number of atoms in the reactants equal to the number of atoms in the products for H, S and K: H: | 2 c_1 = 2 c_3 S: | c_1 = c_4 K: | c_2 = 2 c_4 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: | | H_2S + 2 K ⟶ H_2 + K2S

+ ⟶ + K2S

hydrogen sulfide + potassium ⟶ hydrogen + K2S

Construct the equilibrium constant, K, expression for: H_2S + K ⟶ H_2 + K2S 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: H_2S + 2 K ⟶ H_2 + K2S 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_2S | 1 | -1 K | 2 | -2 H_2 | 1 | 1 K2S | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2S | 1 | -1 | ([H2S])^(-1) K | 2 | -2 | ([K])^(-2) H_2 | 1 | 1 | [H2] K2S | 1 | 1 | [K2S] 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 = ([H2S])^(-1) ([K])^(-2) [H2] [K2S] = ([H2] [K2S])/([H2S] ([K])^2)

Construct the rate of reaction expression for: H_2S + K ⟶ H_2 + K2S 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: H_2S + 2 K ⟶ H_2 + K2S 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_2S | 1 | -1 K | 2 | -2 H_2 | 1 | 1 K2S | 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_2S | 1 | -1 | -(Δ[H2S])/(Δt) K | 2 | -2 | -1/2 (Δ[K])/(Δt) H_2 | 1 | 1 | (Δ[H2])/(Δt) K2S | 1 | 1 | (Δ[K2S])/(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[H2S])/(Δt) = -1/2 (Δ[K])/(Δt) = (Δ[H2])/(Δt) = (Δ[K2S])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen sulfide | potassium | hydrogen | K2S formula | H_2S | K | H_2 | K2S name | hydrogen sulfide | potassium | hydrogen | IUPAC name | hydrogen sulfide | potassium | molecular hydrogen |

| hydrogen sulfide | potassium | hydrogen | K2S molar mass | 34.08 g/mol | 39.0983 g/mol | 2.016 g/mol | 110.26 g/mol phase | gas (at STP) | solid (at STP) | gas (at STP) | melting point | -85 °C | 64 °C | -259.2 °C | boiling point | -60 °C | 760 °C | -252.8 °C | density | 0.001393 g/cm^3 (at 25 °C) | 0.86 g/cm^3 | 8.99×10^-5 g/cm^3 (at 0 °C) | solubility in water | | reacts | | dynamic viscosity | 1.239×10^-5 Pa s (at 25 °C) | | 8.9×10^-6 Pa s (at 25 °C) | odor | | | odorless |