HCl + Au = H2 + AuCl3

HCl (hydrogen chloride) + Au (gold) ⟶ H_2 (hydrogen) + AuCl_3 (gold(III) chloride)

Balance the chemical equation algebraically: HCl + Au ⟶ H_2 + AuCl_3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HCl + c_2 Au ⟶ c_3 H_2 + c_4 AuCl_3 Set the number of atoms in the reactants equal to the number of atoms in the products for Cl, H and Au: Cl: | c_1 = 3 c_4 H: | c_1 = 2 c_3 Au: | 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 = 3 c_2 = 1 c_3 = 3/2 c_4 = 1 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 6 c_2 = 2 c_3 = 3 c_4 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 6 HCl + 2 Au ⟶ 3 H_2 + 2 AuCl_3

+ ⟶ +

hydrogen chloride + gold ⟶ hydrogen + gold(III) chloride

Construct the equilibrium constant, K, expression for: HCl + Au ⟶ H_2 + AuCl_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 HCl + 2 Au ⟶ 3 H_2 + 2 AuCl_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 HCl | 6 | -6 Au | 2 | -2 H_2 | 3 | 3 AuCl_3 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HCl | 6 | -6 | ([HCl])^(-6) Au | 2 | -2 | ([Au])^(-2) H_2 | 3 | 3 | ([H2])^3 AuCl_3 | 2 | 2 | ([AuCl3])^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 = ([HCl])^(-6) ([Au])^(-2) ([H2])^3 ([AuCl3])^2 = (([H2])^3 ([AuCl3])^2)/(([HCl])^6 ([Au])^2)

Construct the rate of reaction expression for: HCl + Au ⟶ H_2 + AuCl_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 HCl + 2 Au ⟶ 3 H_2 + 2 AuCl_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 HCl | 6 | -6 Au | 2 | -2 H_2 | 3 | 3 AuCl_3 | 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 HCl | 6 | -6 | -1/6 (Δ[HCl])/(Δt) Au | 2 | -2 | -1/2 (Δ[Au])/(Δt) H_2 | 3 | 3 | 1/3 (Δ[H2])/(Δt) AuCl_3 | 2 | 2 | 1/2 (Δ[AuCl3])/(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[HCl])/(Δt) = -1/2 (Δ[Au])/(Δt) = 1/3 (Δ[H2])/(Δt) = 1/2 (Δ[AuCl3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen chloride | gold | hydrogen | gold(III) chloride formula | HCl | Au | H_2 | AuCl_3 Hill formula | ClH | Au | H_2 | AuCl_3 name | hydrogen chloride | gold | hydrogen | gold(III) chloride IUPAC name | hydrogen chloride | gold | molecular hydrogen | trichlorogold

| hydrogen chloride | gold | hydrogen | gold(III) chloride molar mass | 36.46 g/mol | 196.966569 g/mol | 2.016 g/mol | 303.3 g/mol phase | gas (at STP) | solid (at STP) | gas (at STP) | melting point | -114.17 °C | 1063 °C | -259.2 °C | boiling point | -85 °C | 2856 °C | -252.8 °C | density | 0.00149 g/cm^3 (at 25 °C) | 19.3 g/cm^3 | 8.99×10^-5 g/cm^3 (at 0 °C) | solubility in water | miscible | insoluble | | dynamic viscosity | | | 8.9×10^-6 Pa s (at 25 °C) | odor | | | odorless |