Br2 + KI = I2 + KBr

Br_2 (bromine) + KI (potassium iodide) ⟶ I_2 (iodine) + KBr (potassium bromide)

Balance the chemical equation algebraically: Br_2 + KI ⟶ I_2 + KBr Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Br_2 + c_2 KI ⟶ c_3 I_2 + c_4 KBr Set the number of atoms in the reactants equal to the number of atoms in the products for Br, I and K: Br: | 2 c_1 = c_4 I: | c_2 = 2 c_3 K: | 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 = 2 c_3 = 1 c_4 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | Br_2 + 2 KI ⟶ I_2 + 2 KBr

+ ⟶ +

bromine + potassium iodide ⟶ iodine + potassium bromide

| bromine | potassium iodide | iodine | potassium bromide molecular enthalpy | 0 kJ/mol | -327.9 kJ/mol | 0 kJ/mol | -393.8 kJ/mol total enthalpy | 0 kJ/mol | -655.8 kJ/mol | 0 kJ/mol | -787.6 kJ/mol | H_initial = -655.8 kJ/mol | | H_final = -787.6 kJ/mol | ΔH_rxn^0 | -787.6 kJ/mol - -655.8 kJ/mol = -131.8 kJ/mol (exothermic) | | |

| bromine | potassium iodide | iodine | potassium bromide molecular free energy | 0 kJ/mol | -324.9 kJ/mol | 0 kJ/mol | -380.7 kJ/mol total free energy | 0 kJ/mol | -649.8 kJ/mol | 0 kJ/mol | -761.4 kJ/mol | G_initial = -649.8 kJ/mol | | G_final = -761.4 kJ/mol | ΔG_rxn^0 | -761.4 kJ/mol - -649.8 kJ/mol = -111.6 kJ/mol (exergonic) | | |

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

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

| bromine | potassium iodide | iodine | potassium bromide formula | Br_2 | KI | I_2 | KBr Hill formula | Br_2 | IK | I_2 | BrK name | bromine | potassium iodide | iodine | potassium bromide IUPAC name | molecular bromine | potassium iodide | molecular iodine | potassium bromide

| bromine | potassium iodide | iodine | potassium bromide molar mass | 159.81 g/mol | 166.0028 g/mol | 253.80894 g/mol | 119 g/mol phase | liquid (at STP) | solid (at STP) | solid (at STP) | solid (at STP) melting point | -7.2 °C | 681 °C | 113 °C | 734 °C boiling point | 58.8 °C | 1330 °C | 184 °C | 1435 °C density | 3.119 g/cm^3 | 3.123 g/cm^3 | 4.94 g/cm^3 | 2.75 g/cm^3 solubility in water | insoluble | | | soluble surface tension | 0.0409 N/m | | | dynamic viscosity | 9.44×10^-4 Pa s (at 25 °C) | 0.0010227 Pa s (at 732.9 °C) | 0.00227 Pa s (at 116 °C) |