Kinetics and Thermodynamics

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27 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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During a chemical reaction heat can be
either absorbed or released.



As the reactants become the products
energy can be released


exothermic



As the reactants become the products
energy can be absorbed


endothermic


The energy levels of the reactants and
the products will be different.



ΔH =
Enthaply



The difference in the
energy levels of a reaction.




ΔH
reaction

=
ΔH
products



ΔH
reactants


ΔH is negative for exothermic reactions

ΔH is positive for endothermic reactions


Many reactions require an input of
energy for them to start, this is known as
Activation Energy
.



The ΔH of the reactants, products and
activation energy can be graphed.


The variables of energy
and reaction
path/progress are
graphed.



The amount of energy
required to push the
reactants over the edge,
to start the reaction, is the
activation energy.



Once at this point the
reaction takes place and
products are formed.



The difference in the
energy of the reactants
and products is the
ΔH


In exothermic
reactions energy of
the products is less
than the reactants.



Energy is released
(heat is given off).



ΔH is negative.


Endothermic reactions
usually have a steep
activation energy, because
the energy of the products
is MUCH higher than the
reactants (LOTS of energy
input).



ΔH is positive (energy
absorbed).




Another factor influencing reactions is
known as Entropy (
Δ
S).


Entropy is a measure of the random
disorder in a reaction.


With respect to molecules in phases:


Phase

Amount of Entropy

Solid

Low

Liquid

Medium

Gas

High


Enthalpy and Entropy both influence
reaction rate.


Free energy is a measure of the
available energy to do work.






ΔG =
Δ
H
-

T

Δ
S

Δ
G = Free energy

Δ
H = Enthalpy

Δ
S = Entropy

T = Temperature


Spontaneous reactions occur on their
own, without any outside energy input.


This depends upon
Δ
S,
Δ
H and
Δ
G


Δ
G

Reaction Behavior

Negative

Spontaneous

Zero

Equilibrium

Positive

Will

not proceed on its own