WEEK FOUR DATE:
_________
TOPIC: EXOTHERMIC AND ENDOTHERMIC
REACTIONS
CONTENT
Heat Content (Enthalpy) of a substance.
Types of Heat of Reactions.
Thermodynamics: First and Second Laws.
Entropy and Free energy
ENERGY
Energy is defined as the ability to do work. It exists in
different forms like: heat, light, sound, electrical,
potentials (stored), kinetic etc.
LAWS OF CONSERVATION OF ENERGY
Energy can be changed from one form to another. The
total amount of energy before and after the change
remains the same. This observation is stated in the law of
conservation of energy which states that energy can
neither be created nor destroyed but can be changed
from one form to another.
There are types of energy such as chemical energy, heat
energy, and light energy.
HEAT CONTENT (ENTHALPY) OF A SUBSTANCE
Heat content or Enthalpy of a substance is the
characteristic internal energy possess by the substance,
which is due to the structure and physical state of a
substance. The potential energy is due to the structure
while the kinetic energy is due to the physical state.
Enthalpy of one substance is different from another. Total
enthalpy cannot be measured but only enthalpy change.
Generally, an enthalpy change (∆H) is the heat that would
, be exchanged with the surrounding, that is, it is the
amount of energy involved in a reaction.
Thus,
Enthalpy change = Heat of products – Heat of reactants
That is, ∆H = Hproducts - Hreactants
The enthalpy change of a given reaction is always written
side by side with the given equation and it may be either
a positive or negative value.
Example: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) ∆H = -
57.3kJ
Unit of enthalpy change(∆H) is Joules(J) or kilojoules(kJ)
EXOTHERMIC AND ENDOTHERMIC REACTIONS
EXOTHERMIC REACTION
A chemical reaction in which heat is given off to the
surrounding is known as exothermic reaction. When an
exothermic reaction occurs, heat is liberated and
transferred from the chemicals to the surroundings and
the temperature of the reaction mixture rises. The
reaction vessel will feel hot.
Examples of exothermic reactions include:
1. Reaction between calcium oxide and water
2. Reaction between an acid and a base.
3. Combustion of fuel
4. Corrosion of metals
5. Respiration
In exothermic reaction, enthalpy change is negative since
the heat content of the products is less than the heat
content of the reactants.
ENDOTHERMIC REACTION
_________
TOPIC: EXOTHERMIC AND ENDOTHERMIC
REACTIONS
CONTENT
Heat Content (Enthalpy) of a substance.
Types of Heat of Reactions.
Thermodynamics: First and Second Laws.
Entropy and Free energy
ENERGY
Energy is defined as the ability to do work. It exists in
different forms like: heat, light, sound, electrical,
potentials (stored), kinetic etc.
LAWS OF CONSERVATION OF ENERGY
Energy can be changed from one form to another. The
total amount of energy before and after the change
remains the same. This observation is stated in the law of
conservation of energy which states that energy can
neither be created nor destroyed but can be changed
from one form to another.
There are types of energy such as chemical energy, heat
energy, and light energy.
HEAT CONTENT (ENTHALPY) OF A SUBSTANCE
Heat content or Enthalpy of a substance is the
characteristic internal energy possess by the substance,
which is due to the structure and physical state of a
substance. The potential energy is due to the structure
while the kinetic energy is due to the physical state.
Enthalpy of one substance is different from another. Total
enthalpy cannot be measured but only enthalpy change.
Generally, an enthalpy change (∆H) is the heat that would
, be exchanged with the surrounding, that is, it is the
amount of energy involved in a reaction.
Thus,
Enthalpy change = Heat of products – Heat of reactants
That is, ∆H = Hproducts - Hreactants
The enthalpy change of a given reaction is always written
side by side with the given equation and it may be either
a positive or negative value.
Example: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) ∆H = -
57.3kJ
Unit of enthalpy change(∆H) is Joules(J) or kilojoules(kJ)
EXOTHERMIC AND ENDOTHERMIC REACTIONS
EXOTHERMIC REACTION
A chemical reaction in which heat is given off to the
surrounding is known as exothermic reaction. When an
exothermic reaction occurs, heat is liberated and
transferred from the chemicals to the surroundings and
the temperature of the reaction mixture rises. The
reaction vessel will feel hot.
Examples of exothermic reactions include:
1. Reaction between calcium oxide and water
2. Reaction between an acid and a base.
3. Combustion of fuel
4. Corrosion of metals
5. Respiration
In exothermic reaction, enthalpy change is negative since
the heat content of the products is less than the heat
content of the reactants.
ENDOTHERMIC REACTION
