Al + HI = H2 + AlI3

Al aluminum + HI hydrogen iodide ⟶ H_2 hydrogen + AlI_3 aluminum iodide

Balance the chemical equation algebraically: Al + HI ⟶ H_2 + AlI_3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Al + c_2 HI ⟶ c_3 H_2 + c_4 AlI_3 Set the number of atoms in the reactants equal to the number of atoms in the products for Al, H and I: Al: | c_1 = c_4 H: | c_2 = 2 c_3 I: | c_2 = 3 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_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 3 c_3 = 3/2 c_4 = 1 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 2 c_2 = 6 c_3 = 3 c_4 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 Al + 6 HI ⟶ 3 H_2 + 2 AlI_3

+ ⟶ +

aluminum + hydrogen iodide ⟶ hydrogen + aluminum iodide

| aluminum | hydrogen iodide | hydrogen | aluminum iodide molecular enthalpy | 0 kJ/mol | 26.5 kJ/mol | 0 kJ/mol | -313.8 kJ/mol total enthalpy | 0 kJ/mol | 159 kJ/mol | 0 kJ/mol | -627.6 kJ/mol | H_initial = 159 kJ/mol | | H_final = -627.6 kJ/mol | ΔH_rxn^0 | -627.6 kJ/mol - 159 kJ/mol = -786.6 kJ/mol (exothermic) | | |

Construct the equilibrium constant, K, expression for: Al + HI ⟶ H_2 + AlI_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 Al + 6 HI ⟶ 3 H_2 + 2 AlI_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 Al | 2 | -2 HI | 6 | -6 H_2 | 3 | 3 AlI_3 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression Al | 2 | -2 | ([Al])^(-2) HI | 6 | -6 | ([HI])^(-6) H_2 | 3 | 3 | ([H2])^3 AlI_3 | 2 | 2 | ([AlI3])^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 = ([Al])^(-2) ([HI])^(-6) ([H2])^3 ([AlI3])^2 = (([H2])^3 ([AlI3])^2)/(([Al])^2 ([HI])^6)

Construct the rate of reaction expression for: Al + HI ⟶ H_2 + AlI_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 Al + 6 HI ⟶ 3 H_2 + 2 AlI_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 Al | 2 | -2 HI | 6 | -6 H_2 | 3 | 3 AlI_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 Al | 2 | -2 | -1/2 (Δ[Al])/(Δt) HI | 6 | -6 | -1/6 (Δ[HI])/(Δt) H_2 | 3 | 3 | 1/3 (Δ[H2])/(Δt) AlI_3 | 2 | 2 | 1/2 (Δ[AlI3])/(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[Al])/(Δt) = -1/6 (Δ[HI])/(Δt) = 1/3 (Δ[H2])/(Δt) = 1/2 (Δ[AlI3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| aluminum | hydrogen iodide | hydrogen | aluminum iodide formula | Al | HI | H_2 | AlI_3 name | aluminum | hydrogen iodide | hydrogen | aluminum iodide IUPAC name | aluminum | hydrogen iodide | molecular hydrogen | triiodoalumane

| aluminum | hydrogen iodide | hydrogen | aluminum iodide molar mass | 26.9815385 g/mol | 127.912 g/mol | 2.016 g/mol | 407.69495 g/mol phase | solid (at STP) | gas (at STP) | gas (at STP) | solid (at STP) melting point | 660.4 °C | -50.76 °C | -259.2 °C | 191 °C boiling point | 2460 °C | -35.55 °C | -252.8 °C | 360 °C density | 2.7 g/cm^3 | 0.005228 g/cm^3 (at 25 °C) | 8.99×10^-5 g/cm^3 (at 0 °C) | 3.98 g/cm^3 solubility in water | insoluble | very soluble | | decomposes surface tension | 0.817 N/m | | | dynamic viscosity | 1.5×10^-4 Pa s (at 760 °C) | 0.001321 Pa s (at -39 °C) | 8.9×10^-6 Pa s (at 25 °C) | odor | odorless | | odorless |