Environmental Chemistry. 3. Chemical Kinetics. The study of the rates and mechanisms of chemical reaction. Rate of reaction - the amount of chemical change that takes place in a given interval of time. The Rate of Chemical Reaction.
for a reaction to occur:
-reactant particles must collide
-collision must have a certain minimum amount of energy: Activation Energy
-reactants may require a specific orientation
Activation Energy, Ea
Avg. Energy of Products, PEP
E energy absorbed during the reaction
Avg. Energy of Reactants, PER
For General Reaction:
aA + bB cC + dD
The rate law generally has a form
Rate = k[reactant 1]m[reactant 2]n
For the reaction above,
Rate = k[A]a[B]b
where k in the rate law is called the rate constant
How long will it take the carbon monoxide (CO) concentration in room to decrease by 99 percent after the source of carbon monoxide is removed and the windows are opened? Assume the first order rate constant for removal (due to dilution by incoming clean air) is 1.2/hr. No chemical reaction occurring.
k = Ae –(Ea/RT)
A – preexponential factor (same as k)
Ea – activation energy (kcal/mole)
R - gas constant
T - temperature (K)
The rate constant for carbonaceous biochemical oxygen demand (CBOD) at 20oC is 0.1/day. What is the rate constant at 30oC? Assume Ea = 1.072.
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