I2 + Na = NaI

I_2 iodine + Na sodium ⟶ NaI sodium iodide

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

+ ⟶

iodine + sodium ⟶ sodium iodide

| iodine | sodium | sodium iodide molecular enthalpy | 0 kJ/mol | 0 kJ/mol | -287.8 kJ/mol total enthalpy | 0 kJ/mol | 0 kJ/mol | -575.6 kJ/mol | H_initial = 0 kJ/mol | | H_final = -575.6 kJ/mol ΔH_rxn^0 | -575.6 kJ/mol - 0 kJ/mol = -575.6 kJ/mol (exothermic) | |

| iodine | sodium | sodium iodide molecular entropy | 116.1 J/(mol K) | 51 J/(mol K) | 91 J/(mol K) total entropy | 116.1 J/(mol K) | 102 J/(mol K) | 182 J/(mol K) | S_initial = 218.1 J/(mol K) | | S_final = 182 J/(mol K) ΔS_rxn^0 | 182 J/(mol K) - 218.1 J/(mol K) = -36.13 J/(mol K) (exoentropic) | |

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

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

| iodine | sodium | sodium iodide formula | I_2 | Na | NaI Hill formula | I_2 | Na | INa name | iodine | sodium | sodium iodide IUPAC name | molecular iodine | sodium | sodium iodide

| iodine | sodium | sodium iodide molar mass | 253.80894 g/mol | 22.98976928 g/mol | 149.89424 g/mol phase | solid (at STP) | solid (at STP) | solid (at STP) melting point | 113 °C | 97.8 °C | 661 °C boiling point | 184 °C | 883 °C | 1300 °C density | 4.94 g/cm^3 | 0.968 g/cm^3 | 3.67 g/cm^3 solubility in water | | decomposes | dynamic viscosity | 0.00227 Pa s (at 116 °C) | 1.413×10^-5 Pa s (at 527 °C) | 0.0010446 Pa s (at 691 °C)