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General Chemistry Ch. 6 - Equilibrium
MCAT
6
Chemistry
Undergraduate 1
05/23/2016

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Term
dynamic vs. static equilibrium
Definition

dynamic equilibrium means the rate of the forward reaction is equal to the rate of the reverse reaction; the reactions haven't stopped

static equillibrium means the reactions have stopped

Term
law of mass action
Definition

aA + bB ↔ cC + dD

Keq = ([C]c[D]d)/([A]a[B]b)

if a system is at equilibrium at a constant temperature the above ratio is constant, this defines the position of equilibrium; solids and liquids do not appear in the law of mass action, only gaseous and aqueous species

Term
reaction quotient
Definition

Q = ([C]c[D]d)/([A]a[B]b)

relates the reactant and product concentrations at any given time during a reaction

  • if Q < K, ΔG < 0, an dthe reaction proceeds in the forward direction
  • If Q = Keq, ΔG = 0, and the reaction is in dynamic equilibrium
  • If Q > Keq, ΔG > 0, and the reactions proceeds in the reverse direction 
Term
Le Chatelier's principle
Definition

when a chemical system experiences a stress, it will react so as to restore equilibrium

  • Increasing reactants/decreasing products shift right, decreasing reactants/increasing products shifts left
  • Gaseous system - Increasing pressure(decreasing volume) shifts towards fewer moles of gas, Decreasing pressure(increasing volume) shift towards more moles of gas
  • Temperature changes actually change the equilibrium constant - Increasing temp of endothermic/decreasing temp of exothermic shifts right, Decreasing temp of endothermic/increasing temp of exothermic shifts left
Term
kinetic product
Definition
formed with lower temperatures (smaller heat transfer), are higher in free energy than thermodynamic products; sometimes termed 'fast' products
Term
thermodynamic product
Definition
higher temperature with more heat transfer; lower in free energy than kinetic products and therefore more stable; proceed more slowly but are more spontaneous (more negative ΔG)
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