Br2 + K2S = S + KBr

Br_2 bromine + K2S ⟶ S mixed sulfur + KBr potassium bromide

Balance the chemical equation algebraically: Br_2 + K2S ⟶ S + KBr Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Br_2 + c_2 K2S ⟶ c_3 S + c_4 KBr Set the number of atoms in the reactants equal to the number of atoms in the products for Br, K and S: Br: | 2 c_1 = c_4 K: | 2 c_2 = c_4 S: | 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 = 1 c_3 = 1 c_4 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | Br_2 + K2S ⟶ S + 2 KBr

+ K2S ⟶ +

bromine + K2S ⟶ mixed sulfur + potassium bromide

Construct the equilibrium constant, K, expression for: Br_2 + K2S ⟶ S + KBr 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: Br_2 + K2S ⟶ S + 2 KBr 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 Br_2 | 1 | -1 K2S | 1 | -1 S | 1 | 1 KBr | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression Br_2 | 1 | -1 | ([Br2])^(-1) K2S | 1 | -1 | ([K2S])^(-1) S | 1 | 1 | [S] KBr | 2 | 2 | ([KBr])^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 = ([Br2])^(-1) ([K2S])^(-1) [S] ([KBr])^2 = ([S] ([KBr])^2)/([Br2] [K2S])

Construct the rate of reaction expression for: Br_2 + K2S ⟶ S + KBr 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: Br_2 + K2S ⟶ S + 2 KBr 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 Br_2 | 1 | -1 K2S | 1 | -1 S | 1 | 1 KBr | 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 Br_2 | 1 | -1 | -(Δ[Br2])/(Δt) K2S | 1 | -1 | -(Δ[K2S])/(Δt) S | 1 | 1 | (Δ[S])/(Δt) KBr | 2 | 2 | 1/2 (Δ[KBr])/(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[Br2])/(Δt) = -(Δ[K2S])/(Δt) = (Δ[S])/(Δt) = 1/2 (Δ[KBr])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| bromine | K2S | mixed sulfur | potassium bromide formula | Br_2 | K2S | S | KBr Hill formula | Br_2 | K2S | S | BrK name | bromine | | mixed sulfur | potassium bromide IUPAC name | molecular bromine | | sulfur | potassium bromide

| bromine | K2S | mixed sulfur | potassium bromide molar mass | 159.81 g/mol | 110.26 g/mol | 32.06 g/mol | 119 g/mol phase | liquid (at STP) | | solid (at STP) | solid (at STP) melting point | -7.2 °C | | 112.8 °C | 734 °C boiling point | 58.8 °C | | 444.7 °C | 1435 °C density | 3.119 g/cm^3 | | 2.07 g/cm^3 | 2.75 g/cm^3 solubility in water | insoluble | | | soluble surface tension | 0.0409 N/m | | | dynamic viscosity | 9.44×10^-4 Pa s (at 25 °C) | | |