I2 + KBr = Br2 + KI

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

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

+ ⟶ +

iodine + potassium bromide ⟶ bromine + potassium iodide

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

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

Construct the equilibrium constant, K, expression for: I_2 + KBr ⟶ Br_2 + KI 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 + 2 KBr ⟶ Br_2 + 2 KI 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 KBr | 2 | -2 Br_2 | 1 | 1 KI | 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) KBr | 2 | -2 | ([KBr])^(-2) Br_2 | 1 | 1 | [Br2] KI | 2 | 2 | ([KI])^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) ([KBr])^(-2) [Br2] ([KI])^2 = ([Br2] ([KI])^2)/([I2] ([KBr])^2)

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

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

| iodine | potassium bromide | bromine | potassium iodide molar mass | 253.80894 g/mol | 119 g/mol | 159.81 g/mol | 166.0028 g/mol phase | solid (at STP) | solid (at STP) | liquid (at STP) | solid (at STP) melting point | 113 °C | 734 °C | -7.2 °C | 681 °C boiling point | 184 °C | 1435 °C | 58.8 °C | 1330 °C density | 4.94 g/cm^3 | 2.75 g/cm^3 | 3.119 g/cm^3 | 3.123 g/cm^3 solubility in water | | soluble | 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) | 0.0010227 Pa s (at 732.9 °C)