H2S + KNO2 = K2S + HNO2

H_2S (hydrogen sulfide) + KNO_2 (potassium nitrite) ⟶ K2S + HNO_2 (nitrous acid)

Balance the chemical equation algebraically: H_2S + KNO_2 ⟶ K2S + HNO_2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2S + c_2 KNO_2 ⟶ c_3 K2S + c_4 HNO_2 Set the number of atoms in the reactants equal to the number of atoms in the products for H, S, K, N and O: H: | 2 c_1 = c_4 S: | c_1 = c_3 K: | c_2 = 2 c_3 N: | c_2 = c_4 O: | 2 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 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | H_2S + 2 KNO_2 ⟶ K2S + 2 HNO_2

+ ⟶ K2S +

hydrogen sulfide + potassium nitrite ⟶ K2S + nitrous acid

Construct the equilibrium constant, K, expression for: H_2S + KNO_2 ⟶ K2S + HNO_2 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 KNO_2 ⟶ K2S + 2 HNO_2 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 KNO_2 | 2 | -2 K2S | 1 | 1 HNO_2 | 2 | 2 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) KNO_2 | 2 | -2 | ([KNO2])^(-2) K2S | 1 | 1 | [K2S] HNO_2 | 2 | 2 | ([HNO2])^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 = ([H2S])^(-1) ([KNO2])^(-2) [K2S] ([HNO2])^2 = ([K2S] ([HNO2])^2)/([H2S] ([KNO2])^2)

Construct the rate of reaction expression for: H_2S + KNO_2 ⟶ K2S + HNO_2 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 KNO_2 ⟶ K2S + 2 HNO_2 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 KNO_2 | 2 | -2 K2S | 1 | 1 HNO_2 | 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 H_2S | 1 | -1 | -(Δ[H2S])/(Δt) KNO_2 | 2 | -2 | -1/2 (Δ[KNO2])/(Δt) K2S | 1 | 1 | (Δ[K2S])/(Δt) HNO_2 | 2 | 2 | 1/2 (Δ[HNO2])/(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[KNO2])/(Δt) = (Δ[K2S])/(Δt) = 1/2 (Δ[HNO2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen sulfide | potassium nitrite | K2S | nitrous acid formula | H_2S | KNO_2 | K2S | HNO_2 name | hydrogen sulfide | potassium nitrite | | nitrous acid

| hydrogen sulfide | potassium nitrite | K2S | nitrous acid molar mass | 34.08 g/mol | 85.103 g/mol | 110.26 g/mol | 47.013 g/mol phase | gas (at STP) | solid (at STP) | | melting point | -85 °C | 350 °C | | boiling point | -60 °C | | | density | 0.001393 g/cm^3 (at 25 °C) | 1.915 g/cm^3 | | dynamic viscosity | 1.239×10^-5 Pa s (at 25 °C) | | |