O2 + FeS2 = SO2 + Fe2S3

O_2 oxygen + FeS_2 pyrite ⟶ SO_2 sulfur dioxide + Fe2S3

Balance the chemical equation algebraically: O_2 + FeS_2 ⟶ SO_2 + Fe2S3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 O_2 + c_2 FeS_2 ⟶ c_3 SO_2 + c_4 Fe2S3 Set the number of atoms in the reactants equal to the number of atoms in the products for O, Fe and S: O: | 2 c_1 = 2 c_3 Fe: | c_2 = 2 c_4 S: | 2 c_2 = c_3 + 3 c_4 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 = 1 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | O_2 + 2 FeS_2 ⟶ SO_2 + Fe2S3

+ ⟶ + Fe2S3

oxygen + pyrite ⟶ sulfur dioxide + Fe2S3

Construct the equilibrium constant, K, expression for: O_2 + FeS_2 ⟶ SO_2 + Fe2S3 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: O_2 + 2 FeS_2 ⟶ SO_2 + Fe2S3 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 O_2 | 1 | -1 FeS_2 | 2 | -2 SO_2 | 1 | 1 Fe2S3 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression O_2 | 1 | -1 | ([O2])^(-1) FeS_2 | 2 | -2 | ([FeS2])^(-2) SO_2 | 1 | 1 | [SO2] Fe2S3 | 1 | 1 | [Fe2S3] 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 = ([O2])^(-1) ([FeS2])^(-2) [SO2] [Fe2S3] = ([SO2] [Fe2S3])/([O2] ([FeS2])^2)

Construct the rate of reaction expression for: O_2 + FeS_2 ⟶ SO_2 + Fe2S3 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: O_2 + 2 FeS_2 ⟶ SO_2 + Fe2S3 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 O_2 | 1 | -1 FeS_2 | 2 | -2 SO_2 | 1 | 1 Fe2S3 | 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 O_2 | 1 | -1 | -(Δ[O2])/(Δt) FeS_2 | 2 | -2 | -1/2 (Δ[FeS2])/(Δt) SO_2 | 1 | 1 | (Δ[SO2])/(Δt) Fe2S3 | 1 | 1 | (Δ[Fe2S3])/(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[O2])/(Δt) = -1/2 (Δ[FeS2])/(Δt) = (Δ[SO2])/(Δt) = (Δ[Fe2S3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| oxygen | pyrite | sulfur dioxide | Fe2S3 formula | O_2 | FeS_2 | SO_2 | Fe2S3 Hill formula | O_2 | FeS_2 | O_2S | Fe2S3 name | oxygen | pyrite | sulfur dioxide | IUPAC name | molecular oxygen | bis(sulfanylidene)iron | sulfur dioxide |

| oxygen | pyrite | sulfur dioxide | Fe2S3 molar mass | 31.998 g/mol | 120 g/mol | 64.06 g/mol | 207.9 g/mol phase | gas (at STP) | | gas (at STP) | melting point | -218 °C | | -73 °C | boiling point | -183 °C | | -10 °C | density | 0.001429 g/cm^3 (at 0 °C) | 4.89 g/cm^3 | 0.002619 g/cm^3 (at 25 °C) | surface tension | 0.01347 N/m | | 0.02859 N/m | dynamic viscosity | 2.055×10^-5 Pa s (at 25 °C) | | 1.282×10^-5 Pa s (at 25 °C) | odor | odorless | odorless | |