H2O + Al = H2 + Al(OH)2

H_2O water + Al aluminum ⟶ H_2 hydrogen + Al(OH)2

Balance the chemical equation algebraically: H_2O + Al ⟶ H_2 + Al(OH)2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2O + c_2 Al ⟶ c_3 H_2 + c_4 Al(OH)2 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O and Al: H: | 2 c_1 = 2 c_3 + 2 c_4 O: | c_1 = 2 c_4 Al: | 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 H_2O + Al ⟶ H_2 + Al(OH)2

+ ⟶ + Al(OH)2

water + aluminum ⟶ hydrogen + Al(OH)2

Construct the equilibrium constant, K, expression for: H_2O + Al ⟶ H_2 + Al(OH)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: 2 H_2O + Al ⟶ H_2 + Al(OH)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 H_2O | 2 | -2 Al | 1 | -1 H_2 | 1 | 1 Al(OH)2 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2O | 2 | -2 | ([H2O])^(-2) Al | 1 | -1 | ([Al])^(-1) H_2 | 1 | 1 | [H2] Al(OH)2 | 1 | 1 | [Al(OH)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 = ([H2O])^(-2) ([Al])^(-1) [H2] [Al(OH)2] = ([H2] [Al(OH)2])/(([H2O])^2 [Al])

Construct the rate of reaction expression for: H_2O + Al ⟶ H_2 + Al(OH)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: 2 H_2O + Al ⟶ H_2 + Al(OH)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 H_2O | 2 | -2 Al | 1 | -1 H_2 | 1 | 1 Al(OH)2 | 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 H_2O | 2 | -2 | -1/2 (Δ[H2O])/(Δt) Al | 1 | -1 | -(Δ[Al])/(Δt) H_2 | 1 | 1 | (Δ[H2])/(Δt) Al(OH)2 | 1 | 1 | (Δ[Al(OH)2])/(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[H2O])/(Δt) = -(Δ[Al])/(Δt) = (Δ[H2])/(Δt) = (Δ[Al(OH)2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| water | aluminum | hydrogen | Al(OH)2 formula | H_2O | Al | H_2 | Al(OH)2 Hill formula | H_2O | Al | H_2 | H2AlO2 name | water | aluminum | hydrogen | IUPAC name | water | aluminum | molecular hydrogen |

| water | aluminum | hydrogen | Al(OH)2 molar mass | 18.015 g/mol | 26.9815385 g/mol | 2.016 g/mol | 60.996 g/mol phase | liquid (at STP) | solid (at STP) | gas (at STP) | melting point | 0 °C | 660.4 °C | -259.2 °C | boiling point | 99.9839 °C | 2460 °C | -252.8 °C | density | 1 g/cm^3 | 2.7 g/cm^3 | 8.99×10^-5 g/cm^3 (at 0 °C) | solubility in water | | insoluble | | surface tension | 0.0728 N/m | 0.817 N/m | | dynamic viscosity | 8.9×10^-4 Pa s (at 25 °C) | 1.5×10^-4 Pa s (at 760 °C) | 8.9×10^-6 Pa s (at 25 °C) | odor | odorless | odorless | odorless |