HCl + SiO2 = H2O + SiCl4

HCl hydrogen chloride + SiO_2 silicon dioxide ⟶ H_2O water + SiCl_4 silicon tetrachloride

Balance the chemical equation algebraically: HCl + SiO_2 ⟶ H_2O + SiCl_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HCl + c_2 SiO_2 ⟶ c_3 H_2O + c_4 SiCl_4 Set the number of atoms in the reactants equal to the number of atoms in the products for Cl, H, O and Si: Cl: | c_1 = 4 c_4 H: | c_1 = 2 c_3 O: | 2 c_2 = c_3 Si: | 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 = 4 c_2 = 1 c_3 = 2 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 4 HCl + SiO_2 ⟶ 2 H_2O + SiCl_4

+ ⟶ +

hydrogen chloride + silicon dioxide ⟶ water + silicon tetrachloride

| hydrogen chloride | silicon dioxide | water | silicon tetrachloride molecular free energy | -95.3 kJ/mol | -856 kJ/mol | -237.1 kJ/mol | -620 kJ/mol total free energy | -381.2 kJ/mol | -856 kJ/mol | -474.2 kJ/mol | -620 kJ/mol | G_initial = -1237 kJ/mol | | G_final = -1094 kJ/mol | ΔG_rxn^0 | -1094 kJ/mol - -1237 kJ/mol = 143 kJ/mol (endergonic) | | |

| hydrogen chloride | silicon dioxide | water | silicon tetrachloride molecular entropy | 187 J/(mol K) | 42 J/(mol K) | 69.91 J/(mol K) | 240 J/(mol K) total entropy | 748 J/(mol K) | 42 J/(mol K) | 139.8 J/(mol K) | 240 J/(mol K) | S_initial = 790 J/(mol K) | | S_final = 379.8 J/(mol K) | ΔS_rxn^0 | 379.8 J/(mol K) - 790 J/(mol K) = -410.2 J/(mol K) (exoentropic) | | |

Construct the equilibrium constant, K, expression for: HCl + SiO_2 ⟶ H_2O + SiCl_4 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: 4 HCl + SiO_2 ⟶ 2 H_2O + SiCl_4 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 | 4 | -4 SiO_2 | 1 | -1 H_2O | 2 | 2 SiCl_4 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HCl | 4 | -4 | ([HCl])^(-4) SiO_2 | 1 | -1 | ([SiO2])^(-1) H_2O | 2 | 2 | ([H2O])^2 SiCl_4 | 1 | 1 | [SiCl4] 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])^(-4) ([SiO2])^(-1) ([H2O])^2 [SiCl4] = (([H2O])^2 [SiCl4])/(([HCl])^4 [SiO2])

Construct the rate of reaction expression for: HCl + SiO_2 ⟶ H_2O + SiCl_4 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: 4 HCl + SiO_2 ⟶ 2 H_2O + SiCl_4 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 | 4 | -4 SiO_2 | 1 | -1 H_2O | 2 | 2 SiCl_4 | 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 | 4 | -4 | -1/4 (Δ[HCl])/(Δt) SiO_2 | 1 | -1 | -(Δ[SiO2])/(Δt) H_2O | 2 | 2 | 1/2 (Δ[H2O])/(Δt) SiCl_4 | 1 | 1 | (Δ[SiCl4])/(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 = -1/4 (Δ[HCl])/(Δt) = -(Δ[SiO2])/(Δt) = 1/2 (Δ[H2O])/(Δt) = (Δ[SiCl4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen chloride | silicon dioxide | water | silicon tetrachloride formula | HCl | SiO_2 | H_2O | SiCl_4 Hill formula | ClH | O_2Si | H_2O | Cl_4Si name | hydrogen chloride | silicon dioxide | water | silicon tetrachloride IUPAC name | hydrogen chloride | dioxosilane | water | tetrachlorosilane

| hydrogen chloride | silicon dioxide | water | silicon tetrachloride molar mass | 36.46 g/mol | 60.083 g/mol | 18.015 g/mol | 169.9 g/mol phase | gas (at STP) | solid (at STP) | liquid (at STP) | liquid (at STP) melting point | -114.17 °C | 1713 °C | 0 °C | -70 °C boiling point | -85 °C | 2950 °C | 99.9839 °C | 57.6 °C density | 0.00149 g/cm^3 (at 25 °C) | 2.196 g/cm^3 | 1 g/cm^3 | 1.483 g/cm^3 solubility in water | miscible | insoluble | | decomposes surface tension | | | 0.0728 N/m | 0.0196 N/m dynamic viscosity | | | 8.9×10^-4 Pa s (at 25 °C) | 0.0994 Pa s (at 25 °C) odor | | odorless | odorless |