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Flashcards in Gen. Chem 2 Deck (8):
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Kinetics

Kinetics is the study of reaction rate. In other words, how quickly the reaction proceeds. This is usually measured in terms of how fast the reactants disappear by tracking changes in the concentration of the reactants as a function of time (i.e., Molarity/second ; M/s).

1

Thermodynamics

By contrast, the thermodynamics of a reaction reflect the potential reactivity (for example, given infinite reaction time) and includes all measurements of energy flow and relative stability. Thermodynamics produces the quantities ∆H, ∆G, ∆S, Keq and so forth.

2

For a reaction to occur:

1. Reactants must collide with enough energy to overcome the energy of activation.
2. Reactants must be in the correct spatial orientation.

3

Rate

Measured as change in molarity of the reactants per second (M/s)

4

Rate Laws
Assume the following:

1. Reactions only proceed forward (ignore reverse reaction)
2. Only consider the first few seconds of the reaction when there is high concentrations of each reactant and any catalysts (e.g. enzyme)

5

Rate Law Exponents

False idea that exponents are given by coefficients in balanced chemical equation.
Exponents equal the ORDER of each reactant.
Only if specifically told that the reaction is ELEMENTARY do the coefficients equal the exponents in the rate laws.
Always assume they don't.

6

To calculate ORDER of each reactant using experimental data:

1. Find 2 trials where [reactants] in question CHANGED, but all other parameters remained constant (concentration of other reactants, temperature, pressure, etc)
2. Note factor by which [reactant] changed
3. Note factor by which RATE changed across those same 2 trials.
4. Find Y in X^Y=Z

X=factor by which [reactant] changed
Z= factor by which rate changed
Y= order of the reactant
OVERALL ORDER OF REACTION= sum of exponents in the rate law.

7

Rate Law Graphs

Will only be linear when the reaction has only a single reactant OR when it's part of a multiple reactant reaction where the rate is independent of ALL OTHER reactants (zero or in excess)

Zero Order: [A] vs time is linear with slope= -k
1st Order: ln[A] vs time is linear with slope = -k
2nd Order: 1/[A] vs time is linear with slope = k