CHEM 120B Lecture Notes - Lecture 3: Arrhenius Equation, Activated Complex, Collision Frequency

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Temperature Dependence of Reaction Rates
Molecules are driven by random motion; temperature is a handle through
whih this rado otio a e otrolled.
Temperature
When graphed:
o Higher temperatures shifts the peak right; the motions of
molecules increase in their randomness.
Activation Energy
To form new bonds, two reactants must make contact with each
other.
o Upon contact, a transition state called activated complex is
formed.
Highly unstable.
Forms new bond and breaks old bond.
o Activation energy (Ea): the energy required to form an activated
complex.
Always positive.
Has nothing to do with delta-H (enthalpy).
Activation energy deals with the mechanisms of the
pattern of events that takes reactants and forms products.
Activation Energy & Temperature
Increased temperature increases the energy of molecules; this allows
them to overcome the activation energy required.
o Temperature is the distribution of kinetic energy that molecules
have; the measurement of random thermal motion.
Changing temperature changes the value of k in rate laws.
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Document Summary

Molecules are driven by random motion; temperature is a handle through whi(cid:272)h this ra(cid:374)do(cid:373) (cid:373)otio(cid:374) (cid:272)a(cid:374) (cid:271)e (cid:858)(cid:272)o(cid:374)trolled(cid:859). When graphed: higher temperatures shifts the peak right; the motions of molecules increase in their randomness. To form new bonds, two reactants must make contact with each other: upon contact, a transition state called activated complex is formed. Forms new bond and breaks old bond: activation energy (ea): the energy required to form an activated complex. Has nothing to do with delta-h (enthalpy). Activation energy deals with the mechanisms of the pattern of events that takes reactants and forms products. Increased temperature increases the energy of molecules; this allows them to overcome the activation energy required: temperature is the distribution of kinetic energy that molecules have; the measurement of random thermal motion. Changing temperature changes the value of k in rate laws. a / rt. Ea: activation energy measured in joules per mole. R= constant; 8. 314 j per mole * kelvin.

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