HI + HNO2 = H2O + I2 + NO

HI hydrogen iodide + HNO_2 nitrous acid ⟶ H_2O water + I_2 iodine + NO nitric oxide

Balance the chemical equation algebraically: HI + HNO_2 ⟶ H_2O + I_2 + NO Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HI + c_2 HNO_2 ⟶ c_3 H_2O + c_4 I_2 + c_5 NO Set the number of atoms in the reactants equal to the number of atoms in the products for H, I, N and O: H: | c_1 + c_2 = 2 c_3 I: | c_1 = 2 c_4 N: | c_2 = c_5 O: | 2 c_2 = c_3 + c_5 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_4 = 1 and solve the system of equations for the remaining coefficients: c_1 = 2 c_2 = 2 c_3 = 2 c_4 = 1 c_5 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 HI + 2 HNO_2 ⟶ 2 H_2O + I_2 + 2 NO

+ ⟶ + +

hydrogen iodide + nitrous acid ⟶ water + iodine + nitric oxide

Construct the equilibrium constant, K, expression for: HI + HNO_2 ⟶ H_2O + I_2 + NO 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 HI + 2 HNO_2 ⟶ 2 H_2O + I_2 + 2 NO 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 HI | 2 | -2 HNO_2 | 2 | -2 H_2O | 2 | 2 I_2 | 1 | 1 NO | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HI | 2 | -2 | ([HI])^(-2) HNO_2 | 2 | -2 | ([HNO2])^(-2) H_2O | 2 | 2 | ([H2O])^2 I_2 | 1 | 1 | [I2] NO | 2 | 2 | ([NO])^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 = ([HI])^(-2) ([HNO2])^(-2) ([H2O])^2 [I2] ([NO])^2 = (([H2O])^2 [I2] ([NO])^2)/(([HI])^2 ([HNO2])^2)

Construct the rate of reaction expression for: HI + HNO_2 ⟶ H_2O + I_2 + NO 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 HI + 2 HNO_2 ⟶ 2 H_2O + I_2 + 2 NO 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 HI | 2 | -2 HNO_2 | 2 | -2 H_2O | 2 | 2 I_2 | 1 | 1 NO | 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 HI | 2 | -2 | -1/2 (Δ[HI])/(Δt) HNO_2 | 2 | -2 | -1/2 (Δ[HNO2])/(Δt) H_2O | 2 | 2 | 1/2 (Δ[H2O])/(Δt) I_2 | 1 | 1 | (Δ[I2])/(Δt) NO | 2 | 2 | 1/2 (Δ[NO])/(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[HI])/(Δt) = -1/2 (Δ[HNO2])/(Δt) = 1/2 (Δ[H2O])/(Δt) = (Δ[I2])/(Δt) = 1/2 (Δ[NO])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen iodide | nitrous acid | water | iodine | nitric oxide formula | HI | HNO_2 | H_2O | I_2 | NO name | hydrogen iodide | nitrous acid | water | iodine | nitric oxide IUPAC name | hydrogen iodide | nitrous acid | water | molecular iodine | nitric oxide