HF = H2 + F2

HF hydrogen fluoride ⟶ H_2 hydrogen + F_2 fluorine

Balance the chemical equation algebraically: HF ⟶ H_2 + F_2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 HF ⟶ c_2 H_2 + c_3 F_2 Set the number of atoms in the reactants equal to the number of atoms in the products for F and H: F: | c_1 = 2 c_3 H: | c_1 = 2 c_2 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 HF ⟶ H_2 + F_2

⟶ +

hydrogen fluoride ⟶ hydrogen + fluorine

| hydrogen fluoride | hydrogen | fluorine molecular enthalpy | -273.3 kJ/mol | 0 kJ/mol | 0 kJ/mol total enthalpy | -546.6 kJ/mol | 0 kJ/mol | 0 kJ/mol | H_initial = -546.6 kJ/mol | H_final = 0 kJ/mol | ΔH_rxn^0 | 0 kJ/mol - -546.6 kJ/mol = 546.6 kJ/mol (endothermic) | |

| hydrogen fluoride | hydrogen | fluorine molecular free energy | -275.4 kJ/mol | 0 kJ/mol | 0 kJ/mol total free energy | -550.8 kJ/mol | 0 kJ/mol | 0 kJ/mol | G_initial = -550.8 kJ/mol | G_final = 0 kJ/mol | ΔG_rxn^0 | 0 kJ/mol - -550.8 kJ/mol = 550.8 kJ/mol (endergonic) | |

| hydrogen fluoride | hydrogen | fluorine molecular entropy | 173.8 J/(mol K) | 115 J/(mol K) | 202.8 J/(mol K) total entropy | 347.6 J/(mol K) | 115 J/(mol K) | 202.8 J/(mol K) | S_initial = 347.6 J/(mol K) | S_final = 317.8 J/(mol K) | ΔS_rxn^0 | 317.8 J/(mol K) - 347.6 J/(mol K) = -29.8 J/(mol K) (exoentropic) | |

Construct the equilibrium constant, K, expression for: HF ⟶ H_2 + F_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 HF ⟶ H_2 + F_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 HF | 2 | -2 H_2 | 1 | 1 F_2 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression HF | 2 | -2 | ([HF])^(-2) H_2 | 1 | 1 | [H2] F_2 | 1 | 1 | [F2] 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 = ([HF])^(-2) [H2] [F2] = ([H2] [F2])/([HF])^2

Construct the rate of reaction expression for: HF ⟶ H_2 + F_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 HF ⟶ H_2 + F_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 HF | 2 | -2 H_2 | 1 | 1 F_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 HF | 2 | -2 | -1/2 (Δ[HF])/(Δt) H_2 | 1 | 1 | (Δ[H2])/(Δt) F_2 | 1 | 1 | (Δ[F2])/(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[HF])/(Δt) = (Δ[H2])/(Δt) = (Δ[F2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen fluoride | hydrogen | fluorine formula | HF | H_2 | F_2 Hill formula | FH | H_2 | F_2 name | hydrogen fluoride | hydrogen | fluorine IUPAC name | hydrogen fluoride | molecular hydrogen | molecular fluorine

| hydrogen fluoride | hydrogen | fluorine molar mass | 20.006 g/mol | 2.016 g/mol | 37.996806326 g/mol phase | gas (at STP) | gas (at STP) | gas (at STP) melting point | -83.36 °C | -259.2 °C | -219.6 °C boiling point | 19.5 °C | -252.8 °C | -188.12 °C density | 8.18×10^-4 g/cm^3 (at 25 °C) | 8.99×10^-5 g/cm^3 (at 0 °C) | 0.001696 g/cm^3 (at 0 °C) solubility in water | miscible | | reacts dynamic viscosity | 1.2571×10^-5 Pa s (at 20 °C) | 8.9×10^-6 Pa s (at 25 °C) | 2.344×10^-5 Pa s (at 25 °C) odor | | odorless |