I2 + KI = KI3

I_2 iodine + KI potassium iodide ⟶ KI3

Balance the chemical equation algebraically: I_2 + KI ⟶ KI3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 I_2 + c_2 KI ⟶ c_3 KI3 Set the number of atoms in the reactants equal to the number of atoms in the products for I and K: I: | 2 c_1 + c_2 = 3 c_3 K: | 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_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 1 c_3 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | I_2 + KI ⟶ KI3

+ ⟶ KI3

iodine + potassium iodide ⟶ KI3

Construct the equilibrium constant, K, expression for: I_2 + KI ⟶ KI3 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 + KI ⟶ KI3 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 KI | 1 | -1 KI3 | 1 | 1 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) KI | 1 | -1 | ([KI])^(-1) KI3 | 1 | 1 | [KI3] 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) ([KI])^(-1) [KI3] = ([KI3])/([I2] [KI])

Construct the rate of reaction expression for: I_2 + KI ⟶ KI3 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 + KI ⟶ KI3 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 KI | 1 | -1 KI3 | 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 I_2 | 1 | -1 | -(Δ[I2])/(Δt) KI | 1 | -1 | -(Δ[KI])/(Δt) KI3 | 1 | 1 | (Δ[KI3])/(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) = -(Δ[KI])/(Δt) = (Δ[KI3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| iodine | potassium iodide | KI3 formula | I_2 | KI | KI3 Hill formula | I_2 | IK | I3K name | iodine | potassium iodide | IUPAC name | molecular iodine | potassium iodide |

| iodine | potassium iodide | KI3 molar mass | 253.80894 g/mol | 166.0028 g/mol | 419.8117 g/mol phase | solid (at STP) | solid (at STP) | melting point | 113 °C | 681 °C | boiling point | 184 °C | 1330 °C | density | 4.94 g/cm^3 | 3.123 g/cm^3 | dynamic viscosity | 0.00227 Pa s (at 116 °C) | 0.0010227 Pa s (at 732.9 °C) |