HCl + FeCl2 = H2 + FeCl3

HCl hydrogen chloride + FeCl_2 iron(II) chloride ⟶ H_2 hydrogen + FeCl_3 iron(III) chloride

Balance the chemical equation algebraically: HCl + FeCl_2 ⟶ H_2 + FeCl_3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HCl + c_2 FeCl_2 ⟶ c_3 H_2 + c_4 FeCl_3 Set the number of atoms in the reactants equal to the number of atoms in the products for Cl, H and Fe: Cl: | c_1 + 2 c_2 = 3 c_4 H: | c_1 = 2 c_3 Fe: | 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_3 = 1 and solve the system of equations for the remaining coefficients: c_1 = 2 c_2 = 2 c_3 = 1 c_4 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 HCl + 2 FeCl_2 ⟶ H_2 + 2 FeCl_3

+ ⟶ +

hydrogen chloride + iron(II) chloride ⟶ hydrogen + iron(III) chloride

| hydrogen chloride | iron(II) chloride | hydrogen | iron(III) chloride molecular enthalpy | -92.3 kJ/mol | -341.8 kJ/mol | 0 kJ/mol | -399.5 kJ/mol total enthalpy | -184.6 kJ/mol | -683.6 kJ/mol | 0 kJ/mol | -799 kJ/mol | H_initial = -868.2 kJ/mol | | H_final = -799 kJ/mol | ΔH_rxn^0 | -799 kJ/mol - -868.2 kJ/mol = 69.2 kJ/mol (endothermic) | | |

| hydrogen chloride | iron(II) chloride | hydrogen | iron(III) chloride molecular free energy | -95.3 kJ/mol | -302.3 kJ/mol | 0 kJ/mol | -334 kJ/mol total free energy | -190.6 kJ/mol | -604.6 kJ/mol | 0 kJ/mol | -668 kJ/mol | G_initial = -795.2 kJ/mol | | G_final = -668 kJ/mol | ΔG_rxn^0 | -668 kJ/mol - -795.2 kJ/mol = 127.2 kJ/mol (endergonic) | | |

Construct the equilibrium constant, K, expression for: HCl + FeCl_2 ⟶ H_2 + FeCl_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: 2 HCl + 2 FeCl_2 ⟶ H_2 + 2 FeCl_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 | 2 | -2 FeCl_2 | 2 | -2 H_2 | 1 | 1 FeCl_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 | 2 | -2 | ([HCl])^(-2) FeCl_2 | 2 | -2 | ([FeCl2])^(-2) H_2 | 1 | 1 | [H2] FeCl_3 | 2 | 2 | ([FeCl3])^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])^(-2) ([FeCl2])^(-2) [H2] ([FeCl3])^2 = ([H2] ([FeCl3])^2)/(([HCl])^2 ([FeCl2])^2)

Construct the rate of reaction expression for: HCl + FeCl_2 ⟶ H_2 + FeCl_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: 2 HCl + 2 FeCl_2 ⟶ H_2 + 2 FeCl_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 | 2 | -2 FeCl_2 | 2 | -2 H_2 | 1 | 1 FeCl_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 | 2 | -2 | -1/2 (Δ[HCl])/(Δt) FeCl_2 | 2 | -2 | -1/2 (Δ[FeCl2])/(Δt) H_2 | 1 | 1 | (Δ[H2])/(Δt) FeCl_3 | 2 | 2 | 1/2 (Δ[FeCl3])/(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[HCl])/(Δt) = -1/2 (Δ[FeCl2])/(Δt) = (Δ[H2])/(Δt) = 1/2 (Δ[FeCl3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen chloride | iron(II) chloride | hydrogen | iron(III) chloride formula | HCl | FeCl_2 | H_2 | FeCl_3 Hill formula | ClH | Cl_2Fe | H_2 | Cl_3Fe name | hydrogen chloride | iron(II) chloride | hydrogen | iron(III) chloride IUPAC name | hydrogen chloride | dichloroiron | molecular hydrogen | trichloroiron

| hydrogen chloride | iron(II) chloride | hydrogen | iron(III) chloride molar mass | 36.46 g/mol | 126.7 g/mol | 2.016 g/mol | 162.2 g/mol phase | gas (at STP) | solid (at STP) | gas (at STP) | solid (at STP) melting point | -114.17 °C | 677 °C | -259.2 °C | 304 °C boiling point | -85 °C | | -252.8 °C | density | 0.00149 g/cm^3 (at 25 °C) | 3.16 g/cm^3 | 8.99×10^-5 g/cm^3 (at 0 °C) | solubility in water | miscible | | | dynamic viscosity | | | 8.9×10^-6 Pa s (at 25 °C) | odor | | | odorless |