I2 + Sb = Sb2I5

I_2 iodine + Sb gray antimony ⟶ Sb2I5

Balance the chemical equation algebraically: I_2 + Sb ⟶ Sb2I5 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 I_2 + c_2 Sb ⟶ c_3 Sb2I5 Set the number of atoms in the reactants equal to the number of atoms in the products for I and Sb: I: | 2 c_1 = 5 c_3 Sb: | c_2 = 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_3 = 1 and solve the system of equations for the remaining coefficients: c_1 = 5/2 c_2 = 2 c_3 = 1 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 5 c_2 = 4 c_3 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 5 I_2 + 4 Sb ⟶ 2 Sb2I5

+ ⟶ Sb2I5

iodine + gray antimony ⟶ Sb2I5

Construct the equilibrium constant, K, expression for: I_2 + Sb ⟶ Sb2I5 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: 5 I_2 + 4 Sb ⟶ 2 Sb2I5 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 | 5 | -5 Sb | 4 | -4 Sb2I5 | 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 | 5 | -5 | ([I2])^(-5) Sb | 4 | -4 | ([Sb])^(-4) Sb2I5 | 2 | 2 | ([Sb2I5])^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])^(-5) ([Sb])^(-4) ([Sb2I5])^2 = ([Sb2I5])^2/(([I2])^5 ([Sb])^4)

Construct the rate of reaction expression for: I_2 + Sb ⟶ Sb2I5 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: 5 I_2 + 4 Sb ⟶ 2 Sb2I5 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 | 5 | -5 Sb | 4 | -4 Sb2I5 | 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 | 5 | -5 | -1/5 (Δ[I2])/(Δt) Sb | 4 | -4 | -1/4 (Δ[Sb])/(Δt) Sb2I5 | 2 | 2 | 1/2 (Δ[Sb2I5])/(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 = -1/5 (Δ[I2])/(Δt) = -1/4 (Δ[Sb])/(Δt) = 1/2 (Δ[Sb2I5])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| iodine | gray antimony | Sb2I5 formula | I_2 | Sb | Sb2I5 Hill formula | I_2 | Sb | I5Sb2 name | iodine | gray antimony | IUPAC name | molecular iodine | antimony |

| iodine | gray antimony | Sb2I5 molar mass | 253.80894 g/mol | 121.76 g/mol | 878.042 g/mol phase | solid (at STP) | solid (at STP) | melting point | 113 °C | 630 °C | boiling point | 184 °C | 1587 °C | density | 4.94 g/cm^3 | 6.69 g/cm^3 | dynamic viscosity | 0.00227 Pa s (at 116 °C) | |