ch302 notes ch15.1 - CH302 Chapter 15 KINETICS Kinetics:...

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CH302 Chapter 15 KINETICS Kinetics : the study of rates of chemical reactions and their mechanisms R eaction rate : the increase or decrease in concentration of reactant or product per unit time. Units are M.s -1 R eaction mechanism : a series of elementary (molecular) steps by which a reaction occurs. Some reactions that are thermodynamically feasible are kinetically so slow as to be imperceptible . () ( ) OUS INSTANTANE kJ -79 = G O H OH + H SLOW VERY kJ 396 G CO O C o 298 2 - aq + aq o 298 g 2 g 2 diamond Δ = Δ + l 0 0.2 0.4 0.6 0.8 1 1.2 0 5 1 150 200 250 3 Time Concentrations of Reactants & Products [A] & [B] [C] & [D] The Rate of Reaction Consider the reaction A (g) + B (g) C (g) + D (g) Reactants A and B are consumed while products C and D are formed: Note that the reaction does not go to completion. Reaction rates are the rates at which reactants disappear or products appear . For a generic reaction: aA (g) + bB (g) cC (g) + dD (g) The rate of a reaction can be written as: [] [ ] t d D + t c C + or t b B - t a A - = Rate Δ Δ = Δ Δ Δ Δ = Δ Δ Reactants disappear so their concentration decreases over time Products appear so their concentration increases over time How do we get [X]? We follow the concentration of one of the reactants with time as the reaction proceeds by: 1. Withdraw TINY sample and analyse for concentration (this assumes the rate is slow. .) 2. Monitor a change in a physical property that is directly related to concentration (example: IR / Vis / UV spectroscopy) 3. If there is a change in the number of moles of gas we may monitor a change in pressure (or partial pressure)
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ch302 notes ch15.1 - CH302 Chapter 15 KINETICS Kinetics:...

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