Au + H2SeO4 = H2O + Au2SeO3

Au gold + H_2SeO_4 selenic acid ⟶ H_2O water + Au2SeO3

Balance the chemical equation algebraically: Au + H_2SeO_4 ⟶ H_2O + Au2SeO3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Au + c_2 H_2SeO_4 ⟶ c_3 H_2O + c_4 Au2SeO3 Set the number of atoms in the reactants equal to the number of atoms in the products for Au, H, O and Se: Au: | c_1 = 2 c_4 H: | 2 c_2 = 2 c_3 O: | 4 c_2 = c_3 + 3 c_4 Se: | c_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_2 = 1 and solve the system of equations for the remaining coefficients: c_1 = 2 c_2 = 1 c_3 = 1 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 Au + H_2SeO_4 ⟶ H_2O + Au2SeO3

+ ⟶ + Au2SeO3

gold + selenic acid ⟶ water + Au2SeO3

Construct the equilibrium constant, K, expression for: Au + H_2SeO_4 ⟶ H_2O + Au2SeO3 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 Au + H_2SeO_4 ⟶ H_2O + Au2SeO3 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 Au | 2 | -2 H_2SeO_4 | 1 | -1 H_2O | 1 | 1 Au2SeO3 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression Au | 2 | -2 | ([Au])^(-2) H_2SeO_4 | 1 | -1 | ([H2SeO4])^(-1) H_2O | 1 | 1 | [H2O] Au2SeO3 | 1 | 1 | [Au2SeO3] 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 = ([Au])^(-2) ([H2SeO4])^(-1) [H2O] [Au2SeO3] = ([H2O] [Au2SeO3])/(([Au])^2 [H2SeO4])

Construct the rate of reaction expression for: Au + H_2SeO_4 ⟶ H_2O + Au2SeO3 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 Au + H_2SeO_4 ⟶ H_2O + Au2SeO3 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 Au | 2 | -2 H_2SeO_4 | 1 | -1 H_2O | 1 | 1 Au2SeO3 | 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 Au | 2 | -2 | -1/2 (Δ[Au])/(Δt) H_2SeO_4 | 1 | -1 | -(Δ[H2SeO4])/(Δt) H_2O | 1 | 1 | (Δ[H2O])/(Δt) Au2SeO3 | 1 | 1 | (Δ[Au2SeO3])/(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[Au])/(Δt) = -(Δ[H2SeO4])/(Δt) = (Δ[H2O])/(Δt) = (Δ[Au2SeO3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| gold | selenic acid | water | Au2SeO3 formula | Au | H_2SeO_4 | H_2O | Au2SeO3 Hill formula | Au | H_2O_4Se | H_2O | Au2O3Se name | gold | selenic acid | water |

| gold | selenic acid | water | Au2SeO3 molar mass | 196.966569 g/mol | 144.98 g/mol | 18.015 g/mol | 520.9 g/mol phase | solid (at STP) | | liquid (at STP) | melting point | 1063 °C | | 0 °C | boiling point | 2856 °C | | 99.9839 °C | density | 19.3 g/cm^3 | 2.511 g/cm^3 | 1 g/cm^3 | solubility in water | insoluble | | | surface tension | | | 0.0728 N/m | dynamic viscosity | | | 8.9×10^-4 Pa s (at 25 °C) | odor | | | odorless |