is a crucial concept in reactive processes. It determines maximum product yield and influences process design. Understanding equilibrium constants and how to calculate them is key to predicting reaction behavior and completeness.
helps determine equilibrium concentrations, while factors like temperature, pressure, and concentration changes affect equilibrium. explains how systems respond to these disturbances, guiding our understanding of reaction dynamics and .
Chemical Equilibrium Fundamentals
Definition of chemical equilibrium
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Chemical equilibrium occurs when forward and reverse become equal resulting in no net change in concentrations of reactants and products
Significance in reactive processes determines maximum product yield influences process design and operating conditions helps predict reaction behavior and completeness
(K) quantifies reaction extent at equilibrium relates concentrations of reactants and products
Calculation of equilibrium constants
Concentration-based equilibrium constant (Kc) calculated using Kc=[A]a[B]b[C]c[D]d for reaction aA+bB⇌cC+dD with concentrations in mol/L
Pressure-based equilibrium constant (Kp) used for gas-phase reactions calculated as Kp=(PA)a(PB)b(PC)c(PD)d with partial pressures in atm or bar
Relationship between Kc and Kp expressed as Kp=Kc(RT)Δn where Δn represents change in moles of gas
Reaction Extent and Equilibrium Analysis
Determination of equilibrium concentrations
Reaction extent (ξ) measures reaction progress calculated using ξ=νini−ni,0 where ni is moles at equilibrium ni,0 is initial moles and νi is stoichiometric coefficient
Equilibrium concentrations determined by [A]=[A]0−νAξ[B]=[B]0−νBξ[C]=[C]0+νCξ[D]=[D]0+νDξ
Solving for equilibrium concentrations involves:
Substituting expressions into equilibrium constant equation
Solving for reaction extent
Calculating final concentrations using reaction extent
Factors affecting equilibrium
Le Chatelier's Principle states system responds to minimize effects of disturbances (temperature, pressure, concentration changes)
Temperature effects:
Endothermic reactions: K increases with temperature (e.g., N2 + O2 ⇌ 2NO)
Exothermic reactions: K decreases with temperature (e.g., N2 + 3H2 ⇌ 2NH3)
van 't Hoff equation describes : dTdlnK=RT2ΔH∘
Pressure effects only impact gas-phase reactions with change in moles:
Increase in pressure favors side with fewer moles of gas (e.g., N2 + 3H2 ⇌ 2NH3)
Decrease in pressure favors side with more moles of gas (e.g., PCl5 ⇌ PCl3 + Cl2)
Concentration effects:
Adding reactants shifts equilibrium towards products (e.g., adding H2 to N2 + 3H2 ⇌ 2NH3)
Removing products shifts equilibrium towards reactants (e.g., removing NH3 from N2 + 3H2 ⇌ 2NH3)
Inert gases affect equilibrium only by changing total pressure (e.g., adding Ar to N2 + 3H2 ⇌ 2NH3)