I2 + Cr = CrI4

I_2 iodine + Cr chromium ⟶ CrI4

Balance the chemical equation algebraically: I_2 + Cr ⟶ CrI4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 I_2 + c_2 Cr ⟶ c_3 CrI4 Set the number of atoms in the reactants equal to the number of atoms in the products for I and Cr: I: | 2 c_1 = 4 c_3 Cr: | 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 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 I_2 + Cr ⟶ CrI4

+ ⟶ CrI4

iodine + chromium ⟶ CrI4

Construct the equilibrium constant, K, expression for: I_2 + Cr ⟶ CrI4 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 I_2 + Cr ⟶ CrI4 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 | 2 | -2 Cr | 1 | -1 CrI4 | 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 | 2 | -2 | ([I2])^(-2) Cr | 1 | -1 | ([Cr])^(-1) CrI4 | 1 | 1 | [CrI4] 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])^(-2) ([Cr])^(-1) [CrI4] = ([CrI4])/(([I2])^2 [Cr])

Construct the rate of reaction expression for: I_2 + Cr ⟶ CrI4 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 I_2 + Cr ⟶ CrI4 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 | 2 | -2 Cr | 1 | -1 CrI4 | 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 | 2 | -2 | -1/2 (Δ[I2])/(Δt) Cr | 1 | -1 | -(Δ[Cr])/(Δt) CrI4 | 1 | 1 | (Δ[CrI4])/(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[I2])/(Δt) = -(Δ[Cr])/(Δt) = (Δ[CrI4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| iodine | chromium | CrI4 formula | I_2 | Cr | CrI4 name | iodine | chromium | IUPAC name | molecular iodine | chromium |

| iodine | chromium | CrI4 molar mass | 253.80894 g/mol | 51.9961 g/mol | 559.614 g/mol phase | solid (at STP) | solid (at STP) | melting point | 113 °C | 1857 °C | boiling point | 184 °C | 2672 °C | density | 4.94 g/cm^3 | 7.14 g/cm^3 | solubility in water | | insoluble | dynamic viscosity | 0.00227 Pa s (at 116 °C) | | odor | | odorless |