CHEM 004A Lecture Notes - Lecture 1: Kinetic Energy, Jmol, Activation Energy
13 Jun 2018
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Chapter 12 – Kinetics
12.1 – Chemical Reaction Rates
Reactions will be faster at higher temps
Kinetic energy because of movement
If there is enough energy, bonds break, and products are formed
Have to get over the hill, activation energy, is the amount of energy it takes to
do so.
The rate constant is temperature dependent. K increases if you increase temp, even if the concentrations
[ ] stay the same. It is not a direct proportionality though – if the temp doubles, k does not double also.
R is the gas constant = 8.314 J/mol*K, T is temp, Ea is the activation energy
If oleules up wrog, the ods a’t e roke. May ollisios with the wrog aliget ause
bonds to not break.
Fraction of energy needed to get over the hill
- Smaller temp, fraction gets bigger, so the whole thing increases
o Arrhenius equation (exponential)
find more resources at oneclass.com
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At room temp (300K), not much energy in particles, but it increases as temp increases
Molecularity of a single step reaction → tells the number of molecules involved
Unimolecular (1)
Bimolecular (2)
Termolecular (ternary →3)
If 2A + B → products is a single step
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- Have 2 As and 1B so the concentration of A is more important
o With a mechanism, you propose a set of individual steps to get to the products
Types of Single Steps
- Unimolecular
o A → product
o Rate = k [A]
- Bimolecular
o A + B → product
o Rate – k[A][B]
o 2A → product
- Termolecular
o
o
o
o
o All the reactants must come together at the same time for the product to be formed, so
we do’t really go past 3 steps
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
If there is enough energy, bonds break, and products are formed. Have to get over the hill, activation energy, is the amount of energy it takes to do so. K increases if you increase temp, even if the concentrations. It is not a direct proportionality though if the temp doubles, k does not double also. R is the gas constant = 8. 314 j/mol*k, t is temp, ea is the activation energy. Ma(cid:374)y (cid:272)ollisio(cid:374)s with the wro(cid:374)g alig(cid:374)(cid:373)e(cid:374)t (cid:272)ause bonds to not break. Fraction of energy needed to get over the hill. Smaller temp, fraction gets bigger, so the whole thing increases: arrhenius equation (exponential) At room temp (300k), not much energy in particles, but it increases as temp increases. Molecularity of a single step reaction tells the number of molecules involved. If 2a + b products is a single step.
