CH0002 - Lecture 3

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  1. Another Gibbs free energy equation using the Equilibrium constant
    ΔGo = -RT lnK
  2. Thermodynamics tell us whether or not a reaction is ... and ... but it cannot tell us ...
    • ...spontaneous
    • far the reaction will go
    • fast it will be
  3. What does Kinetics tell us?
    • How quickly a reaction will take place. 
    • i.e. the rate of reaction.
  4. What is the rate?
    Rate = Change in concentration / Time
  5. What can you use to measure the concentration?
    • Volumetric methods - Change in volume of gas or increase in pressure
    • Gravimetric methods - Change in mass (if a gas is consumed or evolved by the reaction)
    • Instrumental methods -  Change in physical property which correlates with concentration. e.g colour, electrical conductivity, pH
  6. For a reaction 
    aA + bB --> cC + eE
    What is the rate?
    • rate =
    • -1/d[A]/dt   = 
    • -1/b x d[B]/dt   = 
    • +1/c x d[C]/dt   = 
    • +1/e x d[E]/dt 

    • Where t = time
    • Where d = change in
  7. The rate quation for a chemical reaction shows... the rate depends on the concentrations of the various reactants and products
  8. What is the rate equation?
    rate = d[A]/dt = -k[A]n

    Where is the rate constant and n is the reaction order.

    The minus sign indicates that the concentration of A falls with time. i.e. it is a reactant not a product
  9. In the rate equation, what do the powers to which the concentrations are raised indicate?
    The individual orders of reaction.
  10. Rate = (with powers)
    Rate = k[A]x[B]y[C]z
  11. Total order of reaction is given by...
    sum of the individual orders.

    Total order = x+y+z
  12. First order Units
    • Rate = k[A]1
    • Mol dm-3s-1 = k(mol dm-3)1
    • s-1 = k
  13. Second order units
    • Rate = k[A]2
    • Mol dm-3s-1 = k(mol dm-3)2
    • dm3mol-1s-1 = k
Card Set
CH0002 - Lecture 3
CH0002 - Lecture 3
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