Al + Se = Al2Se3

Al aluminum + Se gray selenium ⟶ Al_2Se_3 aluminum selenide

Balance the chemical equation algebraically: Al + Se ⟶ Al_2Se_3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Al + c_2 Se ⟶ c_3 Al_2Se_3 Set the number of atoms in the reactants equal to the number of atoms in the products for Al and Se: Al: | c_1 = 2 c_3 Se: | c_2 = 3 c_3 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 = 3 c_3 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 Al + 3 Se ⟶ Al_2Se_3

+ ⟶

aluminum + gray selenium ⟶ aluminum selenide

Construct the equilibrium constant, K, expression for: Al + Se ⟶ Al_2Se_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 + 3 Se ⟶ Al_2Se_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 Se | 3 | -3 Al_2Se_3 | 1 | 1 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) Se | 3 | -3 | ([Se])^(-3) Al_2Se_3 | 1 | 1 | [Al2Se3] 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) ([Se])^(-3) [Al2Se3] = ([Al2Se3])/(([Al])^2 ([Se])^3)

Construct the rate of reaction expression for: Al + Se ⟶ Al_2Se_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 + 3 Se ⟶ Al_2Se_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 Se | 3 | -3 Al_2Se_3 | 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 Al | 2 | -2 | -1/2 (Δ[Al])/(Δt) Se | 3 | -3 | -1/3 (Δ[Se])/(Δt) Al_2Se_3 | 1 | 1 | (Δ[Al2Se3])/(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) = -1/3 (Δ[Se])/(Δt) = (Δ[Al2Se3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| aluminum | gray selenium | aluminum selenide formula | Al | Se | Al_2Se_3 name | aluminum | gray selenium | aluminum selenide IUPAC name | aluminum | selenium | aluminum(+3) cation; selenium(-2) anion

| aluminum | gray selenium | aluminum selenide molar mass | 26.9815385 g/mol | 78.971 g/mol | 290.88 g/mol phase | solid (at STP) | solid (at STP) | solid (at STP) melting point | 660.4 °C | 217 °C | 960 °C boiling point | 2460 °C | 684.9 °C | density | 2.7 g/cm^3 | 4.81 g/cm^3 | 3.43 g/cm^3 solubility in water | insoluble | insoluble | decomposes surface tension | 0.817 N/m | 0.1055 N/m | dynamic viscosity | 1.5×10^-4 Pa s (at 760 °C) | 0.221 Pa s (at 220 °C) | odor | odorless | |