I2 + Br2 = IBr3

I_2 iodine + Br_2 bromine ⟶ IBr3

Balance the chemical equation algebraically: I_2 + Br_2 ⟶ IBr3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 I_2 + c_2 Br_2 ⟶ c_3 IBr3 Set the number of atoms in the reactants equal to the number of atoms in the products for I and Br: I: | 2 c_1 = c_3 Br: | 2 c_2 = 3 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_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 3 c_3 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | I_2 + 3 Br_2 ⟶ 2 IBr3

+ ⟶ IBr3

iodine + bromine ⟶ IBr3

Construct the equilibrium constant, K, expression for: I_2 + Br_2 ⟶ IBr3 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: I_2 + 3 Br_2 ⟶ 2 IBr3 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 I_2 | 1 | -1 Br_2 | 3 | -3 IBr3 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression I_2 | 1 | -1 | ([I2])^(-1) Br_2 | 3 | -3 | ([Br2])^(-3) IBr3 | 2 | 2 | ([IBr3])^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 = ([I2])^(-1) ([Br2])^(-3) ([IBr3])^2 = ([IBr3])^2/([I2] ([Br2])^3)

Construct the rate of reaction expression for: I_2 + Br_2 ⟶ IBr3 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: I_2 + 3 Br_2 ⟶ 2 IBr3 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 I_2 | 1 | -1 Br_2 | 3 | -3 IBr3 | 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 I_2 | 1 | -1 | -(Δ[I2])/(Δt) Br_2 | 3 | -3 | -1/3 (Δ[Br2])/(Δt) IBr3 | 2 | 2 | 1/2 (Δ[IBr3])/(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[I2])/(Δt) = -1/3 (Δ[Br2])/(Δt) = 1/2 (Δ[IBr3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| iodine | bromine | IBr3 formula | I_2 | Br_2 | IBr3 Hill formula | I_2 | Br_2 | Br3I name | iodine | bromine | IUPAC name | molecular iodine | molecular bromine |

| iodine | bromine | IBr3 molar mass | 253.80894 g/mol | 159.81 g/mol | 366.62 g/mol phase | solid (at STP) | liquid (at STP) | melting point | 113 °C | -7.2 °C | boiling point | 184 °C | 58.8 °C | density | 4.94 g/cm^3 | 3.119 g/cm^3 | solubility in water | | insoluble | surface tension | | 0.0409 N/m | dynamic viscosity | 0.00227 Pa s (at 116 °C) | 9.44×10^-4 Pa s (at 25 °C) |