chemistry, thermodynamics and chemical reaction

1. Thermodynamics
Mandukhai G

2. 2𝐴𝑢 + 3𝐻2𝑂 → 𝐴𝑢2 𝑂3 + 3𝐻2 𝑏𝑎𝑙𝑎𝑛𝑐𝑒𝑑 𝑏𝑢𝑡 𝑛𝑜𝑡 𝑜𝑐𝑐𝑢𝑟
Proceed only partially
Generating some products but remaining most of the original reactants
unchanged
The rate of reaction can also be affected by other factors such as
temperature
In a reaction, it is important to realize that whether
oIs energy absorbed or released
oFast or slow
oDoes reaction continue until all reactants are converted into products or
is there a point beyond which no additional products formed.

3. Fundamental kinds of energy
1. Potential energy
- stored energy (eg. Water in a dam, energy in a coiled spring waiting to
be released.)
2. Kinetic energy
- Is the energy of motion. (eg. Water falling over a dam, uncoiled
spring)

4. In chemical compounds,
- The attractive force between atoms or ions  a kind of
potential energy
When these attractive force result in the formation of ionic or
covalent bonds,]
- Potential energy  heat ( a kind of kinetic energy)
- The strength of a covalent bond is measured by its bond
dissociation energy.
(the amount of energy that must be supplied to break a bond
and separate the atoms in an isolated gas molecule.

6. - Breaking of the bonds requires an input of energy.
Thus,
 Bond breaking is an endothermic reaction( a process or
reaction that absorbs heat)
∆H is positive
 Bond making is an exothermic reaction. (a process or reaction
that releases heat)
∆H is negative

7. Heat of the reaction or Enthalpy change (∆H)
- The difference between the energies of bond broken in
reactants and the energies of bond formed in products. The
sign of ∆H can e either positive or negative.
Enthalpy (H)
A measure of the amount of energy associated with the
substances involved in a reaction.

8. Law of conservation of energy
Energy can be neither created or destroyed in any physical or
chemical change.
∆H =∑(𝑏𝑜𝑛𝑑 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛 𝑒𝑛𝑒𝑟𝑔𝑦)𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠−∑(𝑏𝑜𝑛𝑑 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛 𝑒𝑛𝑒𝑟𝑔𝑦)𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
The amount of heat absorbed or released in a reverse of reaction is equal
to that released or absorbed in a reverse of reaction,
but ∆H has the opposite sign.

9. Energy from food
1 Cal = 1000kcal = 1kcal = 4184J

10. Why do chemical reactions
occur?
Entropy (S)
Free-energy change ∆G tell us only whether a reaction can occur.

11. Spontaneous process: A process or reaction that, once started, proceeds on its own
without any external influence.
Unspontaneous process: takes place only in the presence of a continuous external
influence.
(Events that lead to lower energy states tend to occur spontaneously)

12. Entropy (S) A measure of the amount
of molecular disorder in a system
Entropy change (∆S) : A measure of the increase
in disorder (∆S=+) or decrease in disorder (∆S= -- )
as a chemical reaction or physical change occurs.

13. Free energy change ∆G: A measure of the change
in free energy as a chemical reaction or physical
change occurs.
It determines spontaneity.

14. How do chemical reactions
occur? Reaction rates
G, activation energy, reaction rate
How fast the reaction will occur?

15. Collision theory
Activation energy (Eact )
The amount of energy necessary for reaction to occur; it determines the reaction rate.
The sizes of the activation energy determines reaction rate, how fast the reaction
occur.

16. Effects of Temperature,
Concentration and Catalysts on
Reaction rates

17. Effects
Increase in
Temperature
Increase in frequency
of collisions
In forcefulness of
collisions
Increase in reaction
rate
Increase in
concentration
Increase in frequency
of collisions
Increase in reaction
rate
Add a catalyst
Lower activation energy
or by orienting the
reacting molecules
propriately
Increase in reaction rate

18. Reversible reactions and
Chemical Equilibrium

19. Reversible reactions: A reaction that can
go in either direction, from products to
reactants or reactants to products.
Chemical equilibrium: A state in which the
rates of forward and reverse reactions are
the same.

20. Equilibrium Equations and
equilibrium Constants

21. Equilibrium constant (K) : Value obtained at a
given temperature from ration of the
concentrations of products and reactants, each
raised to a power equal to its coefficient in the
balanced equation.

22. Le Chatelier’s Principle:
The effect of changing conditions
on Equilibria

23. Le chatelier’s principle:
When a stress is applied
to a system at
equilibrium, equilibrium
shifts to relieve the
stress

24. Regulation of body
temperature
Hypothermiaslowing body
reactionsenergy production drop-death
+cardiac surgery
Hyperthermiaaccelerating
reactionsspeed up pumps-stroke