H3PO4 + Na2CO3 = H2O + CO2 + NaH2PO4

H_3PO_4 phosphoric acid + Na_2CO_3 soda ash ⟶ H_2O water + CO_2 carbon dioxide + NaH_2PO_4 sodium dihydrogen phosphate

Balance the chemical equation algebraically: H_3PO_4 + Na_2CO_3 ⟶ H_2O + CO_2 + NaH_2PO_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_3PO_4 + c_2 Na_2CO_3 ⟶ c_3 H_2O + c_4 CO_2 + c_5 NaH_2PO_4 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, P, C and Na: H: | 3 c_1 = 2 c_3 + 2 c_5 O: | 4 c_1 + 3 c_2 = c_3 + 2 c_4 + 4 c_5 P: | c_1 = c_5 C: | c_2 = c_4 Na: | 2 c_2 = c_5 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 c_4 = 1 c_5 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 H_3PO_4 + Na_2CO_3 ⟶ H_2O + CO_2 + 2 NaH_2PO_4

+ ⟶ + +

phosphoric acid + soda ash ⟶ water + carbon dioxide + sodium dihydrogen phosphate

Construct the equilibrium constant, K, expression for: H_3PO_4 + Na_2CO_3 ⟶ H_2O + CO_2 + NaH_2PO_4 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 H_3PO_4 + Na_2CO_3 ⟶ H_2O + CO_2 + 2 NaH_2PO_4 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_3PO_4 | 2 | -2 Na_2CO_3 | 1 | -1 H_2O | 1 | 1 CO_2 | 1 | 1 NaH_2PO_4 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_3PO_4 | 2 | -2 | ([H3PO4])^(-2) Na_2CO_3 | 1 | -1 | ([Na2CO3])^(-1) H_2O | 1 | 1 | [H2O] CO_2 | 1 | 1 | [CO2] NaH_2PO_4 | 2 | 2 | ([NaH2PO4])^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 = ([H3PO4])^(-2) ([Na2CO3])^(-1) [H2O] [CO2] ([NaH2PO4])^2 = ([H2O] [CO2] ([NaH2PO4])^2)/(([H3PO4])^2 [Na2CO3])

Construct the rate of reaction expression for: H_3PO_4 + Na_2CO_3 ⟶ H_2O + CO_2 + NaH_2PO_4 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 H_3PO_4 + Na_2CO_3 ⟶ H_2O + CO_2 + 2 NaH_2PO_4 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_3PO_4 | 2 | -2 Na_2CO_3 | 1 | -1 H_2O | 1 | 1 CO_2 | 1 | 1 NaH_2PO_4 | 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_3PO_4 | 2 | -2 | -1/2 (Δ[H3PO4])/(Δt) Na_2CO_3 | 1 | -1 | -(Δ[Na2CO3])/(Δt) H_2O | 1 | 1 | (Δ[H2O])/(Δt) CO_2 | 1 | 1 | (Δ[CO2])/(Δt) NaH_2PO_4 | 2 | 2 | 1/2 (Δ[NaH2PO4])/(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[H3PO4])/(Δt) = -(Δ[Na2CO3])/(Δt) = (Δ[H2O])/(Δt) = (Δ[CO2])/(Δt) = 1/2 (Δ[NaH2PO4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| phosphoric acid | soda ash | water | carbon dioxide | sodium dihydrogen phosphate formula | H_3PO_4 | Na_2CO_3 | H_2O | CO_2 | NaH_2PO_4 Hill formula | H_3O_4P | CNa_2O_3 | H_2O | CO_2 | H_2NaO_4P name | phosphoric acid | soda ash | water | carbon dioxide | sodium dihydrogen phosphate IUPAC name | phosphoric acid | disodium carbonate | water | carbon dioxide | sodium dihydrogen phosphate