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Chemistry deals with lots of energy changes that are accompanied by chemical reactions. There are many reactions in which energy, which can neither be created nor destroyed, is converted into heat. If the heat is liberated, then the reaction is exothermic, and if the energy is absorbed, then the reaction is endothermic. Thermochemistry is observed with the measurement of the amount of heat liberated or absorbed.
The enthalpy is a thermodynamic quantity that is defined as the sum of energy stored in the system and the energy used in doing work, and which therefore is equivalent to the total heat of the system.
It is the internal energy of the system that is added to the product pressure and volume.
H = E + PV
Neutralization
It is the name given to the reaction that occurs between an Arrhenius acid and an Arrhenius base. When an acid is added to an aqueous solution of base or vice-versa then the temperature of the solution increases and the heat is evolved along with that salt and water are also formed.
As we all know that enthalpy is the total heat of the system, therefore, enthalpy of neutralization is the change in enthalpy when solutions of an acid and a base react together under standard conditions to produce 1 mole of water along with heat
Q = mcΔT
It is always measured as per mole of water formed. Heat measurements are performed by carrying out the reaction in a special container called a calorimeter. The calorimeter absorbs the heat (Q) that is given off by the neutralisation reaction. All neutralisation reactions are generally exothermic, i.e., heat is given off when acid and base react. The changes in the enthalpy of neutralisation are always negative when strong acids and alkali reactions are involved, and they range very closely between-57 and-58 kj mol-1.
The reaction is :
During the reaction, The heat (Q) released is measured by using
Q=mcpΔT
Where m is the mass of the solution, cp is the specific heat capacity of the solution, T is the temperature change.
Specific heat capacity is the intensive property, and It is the amount of heat required to raise the temperature of a unit mass substance by one degree Celsius.
Enthalpy is obtained by using the formula:
ΔH = -Qn
pH scale – A logarithmic scale on which the hydronium ion concentration in molarity is expressed.An acidic solution has pH < 7 , basic solution has pH > 7 and neutral solution has pH = 7.
NOTE: The amount of heat liberated per mole when a weak acid neutralises a strong base is less than the amount of heat liberated per mole when a strong acid neutralises a strong base.
For example, acetic acid reacts with NaOH to form sodium acetate and water.
Which is also called phenolphthalein,
It is a reaction in which a strong acid reacts with a strong base to form a neutral salt and water as the product and the pH, in this case, will be = 7, this reaction is known as Strong Acid and Strong Base Neutralization.
Example – HCl reacts with NaOH to form sodium chloride and water.
Neutralization of Strong Acid and Weak Base:-
During Strong Acid-Weak Base Neutralization, the base is added to strong acid and the H+ ions are replaced by basic ions and at the neutralization, the salt and water is obtained, the pH, in this case, will be <7.
For Eg. – HCl reacts with ammonium hydroxide to form ammonium chloride and water.
Calculation of Enthalpy of Neutralization:-
By using a calorimeter, The Enthalpy of Neutralization (∆H) is found. It is done by mixing moles (known quantities) of an acid and a base (both initially at the same temperature). It is done by using the formula mcpΔT, ∆t of the mixture the change in temperature measured using the calorimeter.
The formula used to calculate ∆H is mcpΔT
Conclusion:-
Enthalpy of Neutralization is the change in enthalpy when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water.
The heat evolved in the reaction is calculated using the equation dqp= mcpΔT and the heat absorbed by the calorimeter at constant pressure.
∆H is negative in neutralization which implies that it is an exothermic reaction.
