HCl + Na2Se = NaCl + H2Se

HCl hydrogen chloride + Na_2Se sodium selenide ⟶ NaCl sodium chloride + SeH_2 hydrogen selenide

Balance the chemical equation algebraically: HCl + Na_2Se ⟶ NaCl + SeH_2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HCl + c_2 Na_2Se ⟶ c_3 NaCl + c_4 SeH_2 Set the number of atoms in the reactants equal to the number of atoms in the products for Cl, H, Na and Se: Cl: | c_1 = c_3 H: | c_1 = 2 c_4 Na: | 2 c_2 = c_3 Se: | 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 = 2 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 HCl + Na_2Se ⟶ 2 NaCl + SeH_2

+ ⟶ +

hydrogen chloride + sodium selenide ⟶ sodium chloride + hydrogen selenide

Construct the equilibrium constant, K, expression for: HCl + Na_2Se ⟶ NaCl + SeH_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 HCl + Na_2Se ⟶ 2 NaCl + SeH_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 HCl | 2 | -2 Na_2Se | 1 | -1 NaCl | 2 | 2 SeH_2 | 1 | 1 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) Na_2Se | 1 | -1 | ([Na2Se])^(-1) NaCl | 2 | 2 | ([NaCl])^2 SeH_2 | 1 | 1 | [SeH2] 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) ([Na2Se])^(-1) ([NaCl])^2 [SeH2] = (([NaCl])^2 [SeH2])/(([HCl])^2 [Na2Se])

Construct the rate of reaction expression for: HCl + Na_2Se ⟶ NaCl + SeH_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 HCl + Na_2Se ⟶ 2 NaCl + SeH_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 HCl | 2 | -2 Na_2Se | 1 | -1 NaCl | 2 | 2 SeH_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 HCl | 2 | -2 | -1/2 (Δ[HCl])/(Δt) Na_2Se | 1 | -1 | -(Δ[Na2Se])/(Δt) NaCl | 2 | 2 | 1/2 (Δ[NaCl])/(Δt) SeH_2 | 1 | 1 | (Δ[SeH2])/(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) = -(Δ[Na2Se])/(Δt) = 1/2 (Δ[NaCl])/(Δt) = (Δ[SeH2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen chloride | sodium selenide | sodium chloride | hydrogen selenide formula | HCl | Na_2Se | NaCl | SeH_2 Hill formula | ClH | Na_2Se | ClNa | H_2Se name | hydrogen chloride | sodium selenide | sodium chloride | hydrogen selenide IUPAC name | hydrogen chloride | disodium selenium(-2) anion | sodium chloride | hydrogen selenide

| hydrogen chloride | sodium selenide | sodium chloride | hydrogen selenide molar mass | 36.46 g/mol | 124.95 g/mol | 58.44 g/mol | 80.987 g/mol phase | gas (at STP) | solid (at STP) | solid (at STP) | melting point | -114.17 °C | 875 °C | 801 °C | boiling point | -85 °C | | 1413 °C | density | 0.00149 g/cm^3 (at 25 °C) | 2.625 g/cm^3 | 2.16 g/cm^3 | solubility in water | miscible | | soluble | odor | | | odorless |