ZnCl2 + (NH4)2S = NH4Cl + ZnS

ZnCl_2 zinc chloride + (NH_4)_2S diammonium sulfide ⟶ NH_4Cl ammonium chloride + ZnS zinc sulfide

Balance the chemical equation algebraically: ZnCl_2 + (NH_4)_2S ⟶ NH_4Cl + ZnS Add stoichiometric coefficients, c_i, to the reactants and products: c_1 ZnCl_2 + c_2 (NH_4)_2S ⟶ c_3 NH_4Cl + c_4 ZnS Set the number of atoms in the reactants equal to the number of atoms in the products for Cl, Zn, H, N and S: Cl: | 2 c_1 = c_3 Zn: | c_1 = c_4 H: | 8 c_2 = 4 c_3 N: | 2 c_2 = c_3 S: | 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_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 1 c_3 = 2 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | ZnCl_2 + (NH_4)_2S ⟶ 2 NH_4Cl + ZnS

+ ⟶ +

zinc chloride + diammonium sulfide ⟶ ammonium chloride + zinc sulfide

Construct the equilibrium constant, K, expression for: ZnCl_2 + (NH_4)_2S ⟶ NH_4Cl + ZnS 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: ZnCl_2 + (NH_4)_2S ⟶ 2 NH_4Cl + ZnS 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 ZnCl_2 | 1 | -1 (NH_4)_2S | 1 | -1 NH_4Cl | 2 | 2 ZnS | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression ZnCl_2 | 1 | -1 | ([ZnCl2])^(-1) (NH_4)_2S | 1 | -1 | ([(NH4)2S])^(-1) NH_4Cl | 2 | 2 | ([NH4Cl])^2 ZnS | 1 | 1 | [ZnS] 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 = ([ZnCl2])^(-1) ([(NH4)2S])^(-1) ([NH4Cl])^2 [ZnS] = (([NH4Cl])^2 [ZnS])/([ZnCl2] [(NH4)2S])

Construct the rate of reaction expression for: ZnCl_2 + (NH_4)_2S ⟶ NH_4Cl + ZnS 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: ZnCl_2 + (NH_4)_2S ⟶ 2 NH_4Cl + ZnS 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 ZnCl_2 | 1 | -1 (NH_4)_2S | 1 | -1 NH_4Cl | 2 | 2 ZnS | 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 ZnCl_2 | 1 | -1 | -(Δ[ZnCl2])/(Δt) (NH_4)_2S | 1 | -1 | -(Δ[(NH4)2S])/(Δt) NH_4Cl | 2 | 2 | 1/2 (Δ[NH4Cl])/(Δt) ZnS | 1 | 1 | (Δ[ZnS])/(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 = -(Δ[ZnCl2])/(Δt) = -(Δ[(NH4)2S])/(Δt) = 1/2 (Δ[NH4Cl])/(Δt) = (Δ[ZnS])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| zinc chloride | diammonium sulfide | ammonium chloride | zinc sulfide formula | ZnCl_2 | (NH_4)_2S | NH_4Cl | ZnS Hill formula | Cl_2Zn | H_8N_2S | ClH_4N | SZn name | zinc chloride | diammonium sulfide | ammonium chloride | zinc sulfide IUPAC name | zinc dichloride | diammonium sulfide | ammonium chloride | thioxozinc

| zinc chloride | diammonium sulfide | ammonium chloride | zinc sulfide molar mass | 136.3 g/mol | 68.14 g/mol | 53.49 g/mol | 97.44 g/mol phase | solid (at STP) | liquid (at STP) | solid (at STP) | solid (at STP) melting point | 293 °C | -18 °C | 340 °C | 1064 °C density | | 0.997 g/cm^3 | 1.5256 g/cm^3 | 4.1 g/cm^3 solubility in water | soluble | very soluble | soluble | odor | odorless | | |