BCl3 = Cl2 + B

BCl_3 boron trichloride ⟶ Cl_2 chlorine + B boron

Balance the chemical equation algebraically: BCl_3 ⟶ Cl_2 + B Add stoichiometric coefficients, c_i, to the reactants and products: c_1 BCl_3 ⟶ c_2 Cl_2 + c_3 B Set the number of atoms in the reactants equal to the number of atoms in the products for B and Cl: B: | c_1 = c_3 Cl: | 3 c_1 = 2 c_2 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 = 3/2 c_3 = 1 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 2 c_2 = 3 c_3 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 BCl_3 ⟶ 3 Cl_2 + 2 B

⟶ +

boron trichloride ⟶ chlorine + boron

| boron trichloride | chlorine | boron molecular enthalpy | -403.8 kJ/mol | 0 kJ/mol | 0 kJ/mol total enthalpy | -807.6 kJ/mol | 0 kJ/mol | 0 kJ/mol | H_initial = -807.6 kJ/mol | H_final = 0 kJ/mol | ΔH_rxn^0 | 0 kJ/mol - -807.6 kJ/mol = 807.6 kJ/mol (endothermic) | |

Construct the equilibrium constant, K, expression for: BCl_3 ⟶ Cl_2 + B 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 BCl_3 ⟶ 3 Cl_2 + 2 B 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 BCl_3 | 2 | -2 Cl_2 | 3 | 3 B | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression BCl_3 | 2 | -2 | ([BCl3])^(-2) Cl_2 | 3 | 3 | ([Cl2])^3 B | 2 | 2 | ([B])^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 = ([BCl3])^(-2) ([Cl2])^3 ([B])^2 = (([Cl2])^3 ([B])^2)/([BCl3])^2

Construct the rate of reaction expression for: BCl_3 ⟶ Cl_2 + B 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 BCl_3 ⟶ 3 Cl_2 + 2 B 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 BCl_3 | 2 | -2 Cl_2 | 3 | 3 B | 2 | 2 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 BCl_3 | 2 | -2 | -1/2 (Δ[BCl3])/(Δt) Cl_2 | 3 | 3 | 1/3 (Δ[Cl2])/(Δt) B | 2 | 2 | 1/2 (Δ[B])/(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[BCl3])/(Δt) = 1/3 (Δ[Cl2])/(Δt) = 1/2 (Δ[B])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| boron trichloride | chlorine | boron formula | BCl_3 | Cl_2 | B name | boron trichloride | chlorine | boron IUPAC name | trichloroborane | molecular chlorine | boron

| boron trichloride | chlorine | boron molar mass | 117.2 g/mol | 70.9 g/mol | 10.81 g/mol phase | gas (at STP) | gas (at STP) | solid (at STP) melting point | -107 °C | -101 °C | 2075 °C boiling point | 12.4 °C | -34 °C | 4000 °C density | 0.004789 g/cm^3 (at 25 °C) | 0.003214 g/cm^3 (at 0 °C) | 2.34 g/cm^3 solubility in water | decomposes | | insoluble surface tension | 0.0167 N/m | | dynamic viscosity | 0.00104 Pa s (at 10 °C) | |