H2SO4 + O2 + Cr = H2O + H2 + Cr2(SO4)3

H_2SO_4 sulfuric acid + O_2 oxygen + Cr chromium ⟶ H_2O water + H_2 hydrogen + Cr_2(SO_4)_3 chromium sulfate

Balance the chemical equation algebraically: H_2SO_4 + O_2 + Cr ⟶ H_2O + H_2 + Cr_2(SO_4)_3 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2SO_4 + c_2 O_2 + c_3 Cr ⟶ c_4 H_2O + c_5 H_2 + c_6 Cr_2(SO_4)_3 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, S and Cr: H: | 2 c_1 = 2 c_4 + 2 c_5 O: | 4 c_1 + 2 c_2 = c_4 + 12 c_6 S: | c_1 = 3 c_6 Cr: | c_3 = 2 c_6 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_2 = 1 c_3 = (2 c_1)/3 c_4 = 2 c_5 = c_1 - 2 c_6 = c_1/3 The resulting system of equations is still underdetermined, so an additional coefficient must be set arbitrarily. Set c_1 = 6 and solve for the remaining coefficients: c_1 = 6 c_2 = 1 c_3 = 4 c_4 = 2 c_5 = 4 c_6 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 6 H_2SO_4 + O_2 + 4 Cr ⟶ 2 H_2O + 4 H_2 + 2 Cr_2(SO_4)_3

+ + ⟶ + +

sulfuric acid + oxygen + chromium ⟶ water + hydrogen + chromium sulfate

Construct the equilibrium constant, K, expression for: H_2SO_4 + O_2 + Cr ⟶ H_2O + H_2 + Cr_2(SO_4)_3 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: 6 H_2SO_4 + O_2 + 4 Cr ⟶ 2 H_2O + 4 H_2 + 2 Cr_2(SO_4)_3 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 H_2SO_4 | 6 | -6 O_2 | 1 | -1 Cr | 4 | -4 H_2O | 2 | 2 H_2 | 4 | 4 Cr_2(SO_4)_3 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2SO_4 | 6 | -6 | ([H2SO4])^(-6) O_2 | 1 | -1 | ([O2])^(-1) Cr | 4 | -4 | ([Cr])^(-4) H_2O | 2 | 2 | ([H2O])^2 H_2 | 4 | 4 | ([H2])^4 Cr_2(SO_4)_3 | 2 | 2 | ([Cr2(SO4)3])^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 = ([H2SO4])^(-6) ([O2])^(-1) ([Cr])^(-4) ([H2O])^2 ([H2])^4 ([Cr2(SO4)3])^2 = (([H2O])^2 ([H2])^4 ([Cr2(SO4)3])^2)/(([H2SO4])^6 [O2] ([Cr])^4)

Construct the rate of reaction expression for: H_2SO_4 + O_2 + Cr ⟶ H_2O + H_2 + Cr_2(SO_4)_3 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: 6 H_2SO_4 + O_2 + 4 Cr ⟶ 2 H_2O + 4 H_2 + 2 Cr_2(SO_4)_3 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 H_2SO_4 | 6 | -6 O_2 | 1 | -1 Cr | 4 | -4 H_2O | 2 | 2 H_2 | 4 | 4 Cr_2(SO_4)_3 | 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 H_2SO_4 | 6 | -6 | -1/6 (Δ[H2SO4])/(Δt) O_2 | 1 | -1 | -(Δ[O2])/(Δt) Cr | 4 | -4 | -1/4 (Δ[Cr])/(Δt) H_2O | 2 | 2 | 1/2 (Δ[H2O])/(Δt) H_2 | 4 | 4 | 1/4 (Δ[H2])/(Δt) Cr_2(SO_4)_3 | 2 | 2 | 1/2 (Δ[Cr2(SO4)3])/(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 = -1/6 (Δ[H2SO4])/(Δt) = -(Δ[O2])/(Δt) = -1/4 (Δ[Cr])/(Δt) = 1/2 (Δ[H2O])/(Δt) = 1/4 (Δ[H2])/(Δt) = 1/2 (Δ[Cr2(SO4)3])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| sulfuric acid | oxygen | chromium | water | hydrogen | chromium sulfate formula | H_2SO_4 | O_2 | Cr | H_2O | H_2 | Cr_2(SO_4)_3 Hill formula | H_2O_4S | O_2 | Cr | H_2O | H_2 | Cr_2O_12S_3 name | sulfuric acid | oxygen | chromium | water | hydrogen | chromium sulfate IUPAC name | sulfuric acid | molecular oxygen | chromium | water | molecular hydrogen | chromium(+3) cation trisulfate

| sulfuric acid | oxygen | chromium | water | hydrogen | chromium sulfate molar mass | 98.07 g/mol | 31.998 g/mol | 51.9961 g/mol | 18.015 g/mol | 2.016 g/mol | 392.2 g/mol phase | liquid (at STP) | gas (at STP) | solid (at STP) | liquid (at STP) | gas (at STP) | liquid (at STP) melting point | 10.371 °C | -218 °C | 1857 °C | 0 °C | -259.2 °C | boiling point | 279.6 °C | -183 °C | 2672 °C | 99.9839 °C | -252.8 °C | 330 °C density | 1.8305 g/cm^3 | 0.001429 g/cm^3 (at 0 °C) | 7.14 g/cm^3 | 1 g/cm^3 | 8.99×10^-5 g/cm^3 (at 0 °C) | 1.84 g/cm^3 solubility in water | very soluble | | insoluble | | | surface tension | 0.0735 N/m | 0.01347 N/m | | 0.0728 N/m | | dynamic viscosity | 0.021 Pa s (at 25 °C) | 2.055×10^-5 Pa s (at 25 °C) | | 8.9×10^-4 Pa s (at 25 °C) | 8.9×10^-6 Pa s (at 25 °C) | odor | odorless | odorless | odorless | odorless | odorless | odorless