Br2 + Si = SiBr4

Br_2 bromine + Si silicon ⟶ SiBr_4 silicon tetrabromide

Balance the chemical equation algebraically: Br_2 + Si ⟶ SiBr_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Br_2 + c_2 Si ⟶ c_3 SiBr_4 Set the number of atoms in the reactants equal to the number of atoms in the products for Br and Si: Br: | 2 c_1 = 4 c_3 Si: | c_2 = 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_2 = 1 and solve the system of equations for the remaining coefficients: c_1 = 2 c_2 = 1 c_3 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 Br_2 + Si ⟶ SiBr_4

+ ⟶

bromine + silicon ⟶ silicon tetrabromide

Construct the equilibrium constant, K, expression for: Br_2 + Si ⟶ SiBr_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: 2 Br_2 + Si ⟶ SiBr_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 Br_2 | 2 | -2 Si | 1 | -1 SiBr_4 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression Br_2 | 2 | -2 | ([Br2])^(-2) Si | 1 | -1 | ([Si])^(-1) SiBr_4 | 1 | 1 | [SiBr4] 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 = ([Br2])^(-2) ([Si])^(-1) [SiBr4] = ([SiBr4])/(([Br2])^2 [Si])

Construct the rate of reaction expression for: Br_2 + Si ⟶ SiBr_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: 2 Br_2 + Si ⟶ SiBr_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 Br_2 | 2 | -2 Si | 1 | -1 SiBr_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 Br_2 | 2 | -2 | -1/2 (Δ[Br2])/(Δt) Si | 1 | -1 | -(Δ[Si])/(Δt) SiBr_4 | 1 | 1 | (Δ[SiBr4])/(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[Br2])/(Δt) = -(Δ[Si])/(Δt) = (Δ[SiBr4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| bromine | silicon | silicon tetrabromide formula | Br_2 | Si | SiBr_4 Hill formula | Br_2 | Si | Br_4Si name | bromine | silicon | silicon tetrabromide IUPAC name | molecular bromine | silicon | tetrabromosilane

| bromine | silicon | silicon tetrabromide molar mass | 159.81 g/mol | 28.085 g/mol | 347.7 g/mol phase | liquid (at STP) | solid (at STP) | liquid (at STP) melting point | -7.2 °C | 1410 °C | 5 °C boiling point | 58.8 °C | 2355 °C | 153 °C density | 3.119 g/cm^3 | 2.33 g/cm^3 | 2.8 g/cm^3 solubility in water | insoluble | insoluble | reacts surface tension | 0.0409 N/m | | dynamic viscosity | 9.44×10^-4 Pa s (at 25 °C) | |