HNO3 + KI = H2O + NO2 + KIO3

HNO_3 nitric acid + KI potassium iodide ⟶ H_2O water + NO_2 nitrogen dioxide + KIO_3 potassium iodate

Balance the chemical equation algebraically: HNO_3 + KI ⟶ H_2O + NO_2 + KIO_3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HNO_3 + c_2 KI ⟶ c_3 H_2O + c_4 NO_2 + c_5 KIO_3 Set the number of atoms in the reactants equal to the number of atoms in the products for H, N, O, I and K: H: | c_1 = 2 c_3 N: | c_1 = c_4 O: | 3 c_1 = c_3 + 2 c_4 + 3 c_5 I: | c_2 = c_5 K: | c_2 = 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_2 = 1 and solve the system of equations for the remaining coefficients: c_1 = 6 c_2 = 1 c_3 = 3 c_4 = 6 c_5 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 6 HNO_3 + KI ⟶ 3 H_2O + 6 NO_2 + KIO_3

+ ⟶ + +

nitric acid + potassium iodide ⟶ water + nitrogen dioxide + potassium iodate

| nitric acid | potassium iodide | water | nitrogen dioxide | potassium iodate molecular free energy | -80.7 kJ/mol | -324.9 kJ/mol | -237.1 kJ/mol | 51.3 kJ/mol | -418.4 kJ/mol total free energy | -484.2 kJ/mol | -324.9 kJ/mol | -711.3 kJ/mol | 307.8 kJ/mol | -418.4 kJ/mol | G_initial = -809.1 kJ/mol | | G_final = -821.9 kJ/mol | | ΔG_rxn^0 | -821.9 kJ/mol - -809.1 kJ/mol = -12.8 kJ/mol (exergonic) | | | |

Construct the equilibrium constant, K, expression for: HNO_3 + KI ⟶ H_2O + NO_2 + KIO_3 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: 6 HNO_3 + KI ⟶ 3 H_2O + 6 NO_2 + KIO_3 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 HNO_3 | 6 | -6 KI | 1 | -1 H_2O | 3 | 3 NO_2 | 6 | 6 KIO_3 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HNO_3 | 6 | -6 | ([HNO3])^(-6) KI | 1 | -1 | ([KI])^(-1) H_2O | 3 | 3 | ([H2O])^3 NO_2 | 6 | 6 | ([NO2])^6 KIO_3 | 1 | 1 | [KIO3] 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 = ([HNO3])^(-6) ([KI])^(-1) ([H2O])^3 ([NO2])^6 [KIO3] = (([H2O])^3 ([NO2])^6 [KIO3])/(([HNO3])^6 [KI])

Construct the rate of reaction expression for: HNO_3 + KI ⟶ H_2O + NO_2 + KIO_3 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: 6 HNO_3 + KI ⟶ 3 H_2O + 6 NO_2 + KIO_3 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 HNO_3 | 6 | -6 KI | 1 | -1 H_2O | 3 | 3 NO_2 | 6 | 6 KIO_3 | 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 HNO_3 | 6 | -6 | -1/6 (Δ[HNO3])/(Δt) KI | 1 | -1 | -(Δ[KI])/(Δt) H_2O | 3 | 3 | 1/3 (Δ[H2O])/(Δt) NO_2 | 6 | 6 | 1/6 (Δ[NO2])/(Δt) KIO_3 | 1 | 1 | (Δ[KIO3])/(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 = -1/6 (Δ[HNO3])/(Δt) = -(Δ[KI])/(Δt) = 1/3 (Δ[H2O])/(Δt) = 1/6 (Δ[NO2])/(Δt) = (Δ[KIO3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| nitric acid | potassium iodide | water | nitrogen dioxide | potassium iodate formula | HNO_3 | KI | H_2O | NO_2 | KIO_3 Hill formula | HNO_3 | IK | H_2O | NO_2 | IKO_3 name | nitric acid | potassium iodide | water | nitrogen dioxide | potassium iodate IUPAC name | nitric acid | potassium iodide | water | Nitrogen dioxide | potassium iodate

| nitric acid | potassium iodide | water | nitrogen dioxide | potassium iodate molar mass | 63.012 g/mol | 166.0028 g/mol | 18.015 g/mol | 46.005 g/mol | 214 g/mol phase | liquid (at STP) | solid (at STP) | liquid (at STP) | gas (at STP) | solid (at STP) melting point | -41.6 °C | 681 °C | 0 °C | -11 °C | 560 °C boiling point | 83 °C | 1330 °C | 99.9839 °C | 21 °C | density | 1.5129 g/cm^3 | 3.123 g/cm^3 | 1 g/cm^3 | 0.00188 g/cm^3 (at 25 °C) | 1.005 g/cm^3 solubility in water | miscible | | | reacts | surface tension | | | 0.0728 N/m | | dynamic viscosity | 7.6×10^-4 Pa s (at 25 °C) | 0.0010227 Pa s (at 732.9 °C) | 8.9×10^-4 Pa s (at 25 °C) | 4.02×10^-4 Pa s (at 25 °C) | odor | | | odorless | |