HNO3 = H2O + O2 + NO2

HNO_3 (nitric acid) ⟶ H_2O (water) + O_2 (oxygen) + NO_2 (nitrogen dioxide)

Balance the chemical equation algebraically: HNO_3 ⟶ H_2O + O_2 + NO_2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HNO_3 ⟶ c_2 H_2O + c_3 O_2 + c_4 NO_2 Set the number of atoms in the reactants equal to the number of atoms in the products for H, N and O: H: | c_1 = 2 c_2 N: | c_1 = c_4 O: | 3 c_1 = c_2 + 2 c_3 + 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_3 = 1 and solve the system of equations for the remaining coefficients: c_1 = 4 c_2 = 2 c_3 = 1 c_4 = 4 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 4 HNO_3 ⟶ 2 H_2O + O_2 + 4 NO_2

⟶ + +

nitric acid ⟶ water + oxygen + nitrogen dioxide

| nitric acid | water | oxygen | nitrogen dioxide molecular free energy | -80.7 kJ/mol | -237.1 kJ/mol | 231.7 kJ/mol | 51.3 kJ/mol total free energy | -322.8 kJ/mol | -474.2 kJ/mol | 231.7 kJ/mol | 205.2 kJ/mol | G_initial = -322.8 kJ/mol | G_final = -37.3 kJ/mol | | ΔG_rxn^0 | -37.3 kJ/mol - -322.8 kJ/mol = 285.5 kJ/mol (endergonic) | | |

| nitric acid | water | oxygen | nitrogen dioxide molecular entropy | 156 J/(mol K) | 69.91 J/(mol K) | 205 J/(mol K) | 240 J/(mol K) total entropy | 624 J/(mol K) | 139.8 J/(mol K) | 205 J/(mol K) | 960 J/(mol K) | S_initial = 624 J/(mol K) | S_final = 1305 J/(mol K) | | ΔS_rxn^0 | 1305 J/(mol K) - 624 J/(mol K) = 680.8 J/(mol K) (endoentropic) | | |

Construct the equilibrium constant, K, expression for: HNO_3 ⟶ H_2O + O_2 + NO_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: 4 HNO_3 ⟶ 2 H_2O + O_2 + 4 NO_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 HNO_3 | 4 | -4 H_2O | 2 | 2 O_2 | 1 | 1 NO_2 | 4 | 4 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HNO_3 | 4 | -4 | ([HNO3])^(-4) H_2O | 2 | 2 | ([H2O])^2 O_2 | 1 | 1 | [O2] NO_2 | 4 | 4 | ([NO2])^4 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])^(-4) ([H2O])^2 [O2] ([NO2])^4 = (([H2O])^2 [O2] ([NO2])^4)/([HNO3])^4

Construct the rate of reaction expression for: HNO_3 ⟶ H_2O + O_2 + NO_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: 4 HNO_3 ⟶ 2 H_2O + O_2 + 4 NO_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 HNO_3 | 4 | -4 H_2O | 2 | 2 O_2 | 1 | 1 NO_2 | 4 | 4 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 | 4 | -4 | -1/4 (Δ[HNO3])/(Δt) H_2O | 2 | 2 | 1/2 (Δ[H2O])/(Δt) O_2 | 1 | 1 | (Δ[O2])/(Δt) NO_2 | 4 | 4 | 1/4 (Δ[NO2])/(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 = -1/4 (Δ[HNO3])/(Δt) = 1/2 (Δ[H2O])/(Δt) = (Δ[O2])/(Δt) = 1/4 (Δ[NO2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| nitric acid | water | oxygen | nitrogen dioxide formula | HNO_3 | H_2O | O_2 | NO_2 name | nitric acid | water | oxygen | nitrogen dioxide IUPAC name | nitric acid | water | molecular oxygen | Nitrogen dioxide

| nitric acid | water | oxygen | nitrogen dioxide molar mass | 63.012 g/mol | 18.015 g/mol | 31.998 g/mol | 46.005 g/mol phase | liquid (at STP) | liquid (at STP) | gas (at STP) | gas (at STP) melting point | -41.6 °C | 0 °C | -218 °C | -11 °C boiling point | 83 °C | 99.9839 °C | -183 °C | 21 °C density | 1.5129 g/cm^3 | 1 g/cm^3 | 0.001429 g/cm^3 (at 0 °C) | 0.00188 g/cm^3 (at 25 °C) solubility in water | miscible | | | reacts surface tension | | 0.0728 N/m | 0.01347 N/m | dynamic viscosity | 7.6×10^-4 Pa s (at 25 °C) | 8.9×10^-4 Pa s (at 25 °C) | 2.055×10^-5 Pa s (at 25 °C) | 4.02×10^-4 Pa s (at 25 °C) odor | | odorless | odorless |