Input interpretation
H_2 hydrogen + CdS cadmium sulfide ⟶ H_2S hydrogen sulfide + Cd cadmium
Balanced equation
Balance the chemical equation algebraically: H_2 + CdS ⟶ H_2S + Cd Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2 + c_2 CdS ⟶ c_3 H_2S + c_4 Cd Set the number of atoms in the reactants equal to the number of atoms in the products for H, Cd and S: H: | 2 c_1 = 2 c_3 Cd: | 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 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | H_2 + CdS ⟶ H_2S + Cd
Structures
+ ⟶ +
Names
hydrogen + cadmium sulfide ⟶ hydrogen sulfide + cadmium
Reaction thermodynamics
Enthalpy
| hydrogen | cadmium sulfide | hydrogen sulfide | cadmium molecular enthalpy | 0 kJ/mol | -161.9 kJ/mol | -20.6 kJ/mol | 0 kJ/mol total enthalpy | 0 kJ/mol | -161.9 kJ/mol | -20.6 kJ/mol | 0 kJ/mol | H_initial = -161.9 kJ/mol | | H_final = -20.6 kJ/mol | ΔH_rxn^0 | -20.6 kJ/mol - -161.9 kJ/mol = 141.3 kJ/mol (endothermic) | | |
Gibbs free energy
| hydrogen | cadmium sulfide | hydrogen sulfide | cadmium molecular free energy | 0 kJ/mol | -156.5 kJ/mol | -33.4 kJ/mol | 0 kJ/mol total free energy | 0 kJ/mol | -156.5 kJ/mol | -33.4 kJ/mol | 0 kJ/mol | G_initial = -156.5 kJ/mol | | G_final = -33.4 kJ/mol | ΔG_rxn^0 | -33.4 kJ/mol - -156.5 kJ/mol = 123.1 kJ/mol (endergonic) | | |
Entropy
| hydrogen | cadmium sulfide | hydrogen sulfide | cadmium molecular entropy | 115 J/(mol K) | 65 J/(mol K) | 206 J/(mol K) | 52 J/(mol K) total entropy | 115 J/(mol K) | 65 J/(mol K) | 206 J/(mol K) | 52 J/(mol K) | S_initial = 180 J/(mol K) | | S_final = 258 J/(mol K) | ΔS_rxn^0 | 258 J/(mol K) - 180 J/(mol K) = 78 J/(mol K) (endoentropic) | | |
Equilibrium constant
Construct the equilibrium constant, K, expression for: H_2 + CdS ⟶ H_2S + Cd 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: H_2 + CdS ⟶ H_2S + Cd 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_2 | 1 | -1 CdS | 1 | -1 H_2S | 1 | 1 Cd | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2 | 1 | -1 | ([H2])^(-1) CdS | 1 | -1 | ([CdS])^(-1) H_2S | 1 | 1 | [H2S] Cd | 1 | 1 | [Cd] 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 = ([H2])^(-1) ([CdS])^(-1) [H2S] [Cd] = ([H2S] [Cd])/([H2] [CdS])
Rate of reaction
Construct the rate of reaction expression for: H_2 + CdS ⟶ H_2S + Cd 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: H_2 + CdS ⟶ H_2S + Cd 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_2 | 1 | -1 CdS | 1 | -1 H_2S | 1 | 1 Cd | 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 H_2 | 1 | -1 | -(Δ[H2])/(Δt) CdS | 1 | -1 | -(Δ[CdS])/(Δt) H_2S | 1 | 1 | (Δ[H2S])/(Δt) Cd | 1 | 1 | (Δ[Cd])/(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[H2])/(Δt) = -(Δ[CdS])/(Δt) = (Δ[H2S])/(Δt) = (Δ[Cd])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)
Chemical names and formulas
| hydrogen | cadmium sulfide | hydrogen sulfide | cadmium formula | H_2 | CdS | H_2S | Cd name | hydrogen | cadmium sulfide | hydrogen sulfide | cadmium IUPAC name | molecular hydrogen | thioxocadmium | hydrogen sulfide | cadmium
Substance properties
| hydrogen | cadmium sulfide | hydrogen sulfide | cadmium molar mass | 2.016 g/mol | 144.47 g/mol | 34.08 g/mol | 112.414 g/mol phase | gas (at STP) | solid (at STP) | gas (at STP) | solid (at STP) melting point | -259.2 °C | 1400 °C | -85 °C | 320.9 °C boiling point | -252.8 °C | | -60 °C | 765 °C density | 8.99×10^-5 g/cm^3 (at 0 °C) | 4.82 g/cm^3 | 0.001393 g/cm^3 (at 25 °C) | 8.65 g/cm^3 solubility in water | | | | insoluble dynamic viscosity | 8.9×10^-6 Pa s (at 25 °C) | | 1.239×10^-5 Pa s (at 25 °C) | odor | odorless | | | odorless
Units