KI + K2S2O8 = K2SO4 + I2

KI potassium iodide + K_2S_2O_8 potassium persulfate ⟶ K_2SO_4 potassium sulfate + I_2 iodine

Balance the chemical equation algebraically: KI + K_2S_2O_8 ⟶ K_2SO_4 + I_2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 KI + c_2 K_2S_2O_8 ⟶ c_3 K_2SO_4 + c_4 I_2 Set the number of atoms in the reactants equal to the number of atoms in the products for I, K, O and S: I: | c_1 = 2 c_4 K: | c_1 + 2 c_2 = 2 c_3 O: | 8 c_2 = 4 c_3 S: | 2 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 = 2 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 KI + K_2S_2O_8 ⟶ 2 K_2SO_4 + I_2

+ ⟶ +

potassium iodide + potassium persulfate ⟶ potassium sulfate + iodine

Construct the equilibrium constant, K, expression for: KI + K_2S_2O_8 ⟶ K_2SO_4 + I_2 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 KI + K_2S_2O_8 ⟶ 2 K_2SO_4 + I_2 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 KI | 2 | -2 K_2S_2O_8 | 1 | -1 K_2SO_4 | 2 | 2 I_2 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression KI | 2 | -2 | ([KI])^(-2) K_2S_2O_8 | 1 | -1 | ([K2S2O8])^(-1) K_2SO_4 | 2 | 2 | ([K2SO4])^2 I_2 | 1 | 1 | [I2] 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 = ([KI])^(-2) ([K2S2O8])^(-1) ([K2SO4])^2 [I2] = (([K2SO4])^2 [I2])/(([KI])^2 [K2S2O8])

Construct the rate of reaction expression for: KI + K_2S_2O_8 ⟶ K_2SO_4 + I_2 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 KI + K_2S_2O_8 ⟶ 2 K_2SO_4 + I_2 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 KI | 2 | -2 K_2S_2O_8 | 1 | -1 K_2SO_4 | 2 | 2 I_2 | 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 KI | 2 | -2 | -1/2 (Δ[KI])/(Δt) K_2S_2O_8 | 1 | -1 | -(Δ[K2S2O8])/(Δt) K_2SO_4 | 2 | 2 | 1/2 (Δ[K2SO4])/(Δt) I_2 | 1 | 1 | (Δ[I2])/(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[KI])/(Δt) = -(Δ[K2S2O8])/(Δt) = 1/2 (Δ[K2SO4])/(Δt) = (Δ[I2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| potassium iodide | potassium persulfate | potassium sulfate | iodine formula | KI | K_2S_2O_8 | K_2SO_4 | I_2 Hill formula | IK | K_2O_8S_2 | K_2O_4S | I_2 name | potassium iodide | potassium persulfate | potassium sulfate | iodine IUPAC name | potassium iodide | dipotassium sulfonatooxy sulfate | dipotassium sulfate | molecular iodine

| potassium iodide | potassium persulfate | potassium sulfate | iodine molar mass | 166.0028 g/mol | 270.31 g/mol | 174.25 g/mol | 253.80894 g/mol phase | solid (at STP) | solid (at STP) | | solid (at STP) melting point | 681 °C | 100 °C | | 113 °C boiling point | 1330 °C | | | 184 °C density | 3.123 g/cm^3 | 2.477 g/cm^3 | | 4.94 g/cm^3 solubility in water | | soluble | soluble | dynamic viscosity | 0.0010227 Pa s (at 732.9 °C) | | | 0.00227 Pa s (at 116 °C)