I2 + Fe = Fe3I8

I_2 iodine + Fe iron ⟶ Fe3I8

Balance the chemical equation algebraically: I_2 + Fe ⟶ Fe3I8 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 I_2 + c_2 Fe ⟶ c_3 Fe3I8 Set the number of atoms in the reactants equal to the number of atoms in the products for I and Fe: I: | 2 c_1 = 8 c_3 Fe: | 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_3 = 1 and solve the system of equations for the remaining coefficients: c_1 = 4 c_2 = 3 c_3 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 4 I_2 + 3 Fe ⟶ Fe3I8

+ ⟶ Fe3I8

iodine + iron ⟶ Fe3I8

Construct the equilibrium constant, K, expression for: I_2 + Fe ⟶ Fe3I8 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: 4 I_2 + 3 Fe ⟶ Fe3I8 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 | 4 | -4 Fe | 3 | -3 Fe3I8 | 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 | 4 | -4 | ([I2])^(-4) Fe | 3 | -3 | ([Fe])^(-3) Fe3I8 | 1 | 1 | [Fe3I8] 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])^(-4) ([Fe])^(-3) [Fe3I8] = ([Fe3I8])/(([I2])^4 ([Fe])^3)

Construct the rate of reaction expression for: I_2 + Fe ⟶ Fe3I8 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: 4 I_2 + 3 Fe ⟶ Fe3I8 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 | 4 | -4 Fe | 3 | -3 Fe3I8 | 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 | 4 | -4 | -1/4 (Δ[I2])/(Δt) Fe | 3 | -3 | -1/3 (Δ[Fe])/(Δt) Fe3I8 | 1 | 1 | (Δ[Fe3I8])/(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 = -1/4 (Δ[I2])/(Δt) = -1/3 (Δ[Fe])/(Δt) = (Δ[Fe3I8])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| iodine | iron | Fe3I8 formula | I_2 | Fe | Fe3I8 name | iodine | iron | IUPAC name | molecular iodine | iron |

| iodine | iron | Fe3I8 molar mass | 253.80894 g/mol | 55.845 g/mol | 1182.77 g/mol phase | solid (at STP) | solid (at STP) | melting point | 113 °C | 1535 °C | boiling point | 184 °C | 2750 °C | density | 4.94 g/cm^3 | 7.874 g/cm^3 | solubility in water | | insoluble | dynamic viscosity | 0.00227 Pa s (at 116 °C) | |