Equilibria -4

  • Created by: Shannon
  • Created on: 02-04-15 15:02
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  • Equilibria
    • Dynamic equilibria
      • The rate of forward and backward reactions are equal
      • No further changes in concentration
      • Occurs in a close system
    • General rules
      • Heat favours the endothermic direction
      • Increasing pressure will shift equilibrium to the side with the fewest particles
      • On the addition of a reactant or product, equilibrium will shift in the direction that will reduce its effects and conversely
    • Equilibrium constants
      • The equilibrium constant measures the extent to which a reversible reaction will occur at a given temperature
      • Kc = concentration of products / concentration of reactants
      • Can be measures in terms of concentration (Kc) or partial pressures (Kp)
      • Kp = p(products) / p(reactants)
        • Partial pressure = mole fraction x total pressure
          • Mole fraction = moles of chemical species / total number of moles
    • Total and entropy change and the equilibrium constant
      • total entropy = R lnK
        • This means that as a change in temperature causes a change in the total entropy, the value of the equilibrium constant will change too
          • Exothermic reaction - increase in temp will cause entropy of surroundings to be less +ve = total entropy smaller = K smaller
          • Endothermic reaction -increase in temp will cause entropy of surroundings to be less -ve = total entropy larger = K larger
    • Le Chatelier's principle
      • If a system at equilibrium is disturbed, the the position of equilibrium will shift to oppose the effects of the change, and restore equilibrium


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