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Enthalpy of the Neutralization of the strong acids and strong bases is always considered as constant because the strong acids and the strong bases get completely ionized in the solution with the amount of water less than that of acid, known as the dilute solution. So, the resultant Neutralization enthalpy will be constant. The enthalpy is of the neutralization is the change in the enthalpy that takes place when one equivalent of the acid along with one equivalent of the basis undergoes a neutralization reaction for the formation of the salt and water. In the majority of cases, the enthalpy of the neutralization after complete ionization is 57.1 kJ.
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Key Terms: Enthalpy, Neutralization, Acids, Bases, Salt, Standard Enthalpy Change, Alkalis, Chemical Reaction, Ions, pH Level, Ionization, Hydrochloric Acid
Standard Enthalpy Change
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The process in which the solutions of the acid and the solutions of the alkali reaction under the normal conditions produce the 1 mole of water is known as the standard Enthalpy Change. The mode of measurement for the neutralization shift in the enthalpy is per the mole of the water produced in the reaction.
Moreover, the values for the standard enthalpy change are very near including the strong acids and alkalis with the values in the range of the -57 and 58-kilo joule per mole inverse.
Neutralization Reaction
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In the reaction of the acid and the base in the formation of water and salt, the reaction requires the combination of H+ and OH- ions, and this reaction is termed the Neutralization reaction.
There exists a level of pH of 7 for the neutralization of heavy acids and heavy bases. In the neutralization of strong acid and strong base, the Ph value of the neutralization will be lesser than 7 and subsequently, in the case of strong base neutralization with a weak base, the Ph will be greater than 7.
It is also considered, that the salts are formed from the neutralization reaction of equal acid and base weight concentration, the N parts of the acids will be always Neutralize the N parts of the base.
Neutralization Reaction
Read More: Enthalpy Formula
Why do Strong Acids that React with the Strong Alkalis make the Same Value?
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In a given solution of dilute hydrochloric acid, the sodium hydroxide solutions Consist of the sodium ions along with the hydroxide ions. Concerning the solution, the equation for any of the strong acids that are neutralized by a strong alkali is a reaction for the formation of water between the H+ and OH- ions.
The equation of the reaction between the hydrochloric acid and the sodium hydroxide solution is mentioned below –
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
However, the actual representation or the happening of the reaction is somewhat different which is also mentioned below –
OH−(aq) + H+(aq) → H2O(l)
Furthermore, about 99% of the acid does not naturally get ionized in a weak acid, for instance, acetic acid at its ordinary concentration.
The above statement shows that the other enthalpy terms involved in ionizing the acid as well as the reaction between that of the hydrogen ions and the hydroxide ions will include the enthalpy of the neutralization.
Read More: Ionization Enthalpy & its Trends Across the Periodic Table
Experiment to Demonstrate the Enthalpy of the Strong acid and Strong Acid
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Aim
The aim is to determine the enthalpy of the neutralization of the strong acid and the strong base. The strong acid is taken is hydrochloric acid and the strong base is taken is sodium hydroxide.
Theory
The experiment is organized between the strong acid and a strong base with the help of the titration process and the temperature that is resultant which the reaction is proceeding to the equilibrium is noted as readings and further, the heat value is calculated from the same.
Moreover, the enthalpy of the neutralization is the heat evolved when the one gram equivalent of the acid is completely neutralized by a base in a dilute solution.
The chemical equations for the experiment are mentioned below –
H+(aq) + Cl–(aq) + Na+(aq) + OH–(aq) → Na+(aq) + Cl–(aq) + H2O + 13.7 kcal
13.7 kcal of heat is given out and is called the heat of the neutralization for all the strong acids and strong bases.
Also, the 184- obtained a constant value of 13.7Kcal as the heat of neutralization in almost all the cases of the strong acids and strong bases, and this constancy of the neutralization heat is explained based on the ionic theory.
Read More: Acids, Bases and Salts
Materials Required
The materials that are required for the experiment of the enthalpy of the strong acids and strong bases are mentioned below –
- 0.2M sodium hydroxide solution
- Measuring cylinder for content
- Thermometer for measuring the temperature
- Stirrer that is fitted with a cork
- Rubber cork
- Wide Polythene bottle
- Hydrochloric acid (0.2M)
These are the necessities that are required for the experiment to be conducted because the calculations or the readings cannot be identified if the apparatus is not completed.
Procedure
The steps that are mentioned below are important to experiment and all the steps are important to follow orderly –
- Step-1 –Firstly, calculate the water equivalent of the calorimeter.
- Step-2 –Further, place 100ml of the 0.2M of the hydrochloric acid solution in it.
- Step-3 –After this, take the reading of the temperature of the acidic solution.
- Step-4 -Furthermore, take a separate vessel and pour 0.2M sodium hydroxide solution into it.
- Step-5 –Take the reading of the initial temperature of the sodium hydroxide.
- Step-6 –Wait until both the temperatures attain the same temperature.
- Step-7 –After the temperature is kept the same, transfer the sodium hydroxide solution of 100ML into the hydrochloric in one instance fast.
- Step-8 –After transferring, fit the cork immediately.
- Step-9 –After this, stir the solution and take the reading.
- Step-10 –Take frequent readings until the temperature is kept constant.
- Step-11 –Properly, take the reading when the temperature reached the highest.
- Step-12 –Calculate the heat evolved when the two solutions are mixed in the ratio proportion method.
Read More: Difference Between Acid and Base
Observation
The table for the observation that is taken from the above experiment are mentioned below –
- Initial temperature = t1oC
- Final temperature = t2oC
- Change in the temperature = (t1 – t2)oC
- Mass of the mixture solution after the neutralization process = 200 gram
- Water equivalent of calorimeter = W gram
Calculations
The change in the enthalpy during the neutralization of 100Ml of 0.2M HCL
= (200*W)* (t1 – t2)*4
However, the change in the enthalpy during the neutralization of 1000ML of 1M HCL
= ((200*W)* (t1 – t2)*4.2 / 0.2 )/(1000/100)
Precautions
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The precaution that has to be taken while experimenting for safety purposes are mentioned below–
- The solution’s specific heat is taken as the 4.189J/g.
- Due to radiation, little amount of heat is lost in the environment.
- The density of the solution is assumed to be 1g/ml.
- HCL and Sodium hydroxide is assumed to be 100%.
- All the readings must be taken carefully.
Read More: Enthalpy and Entropy
Things to Remember
- It is mandatory to know that the enthalpy for the neutralization is always constant for the strong acid and strong
- The reaction in which the heat is given out is known as the exothermic reaction
- The reaction in which heat is absorbed during the reaction is known as the endothermic reaction.
- 13.7 kcal of heat is given out and is called the heat of the neutralization for all the strong acids and strong bases.
- Furthermore, about 99% of the acid does not naturally get ionized in a weak acid, for instance, acetic acid at its ordinary concentration.
Sample Questions
Ques. Explain the endothermic reaction and exothermic reactions with examples? (3 Marks)
Ans.The reaction in which the heat is absorbed is called the endothermic reaction. Examples of the endothermic reaction are – Melting of the ice cubes, Evaporating liquid water, and so on. Subsequently, the reaction in which the heat is evolved is known as the exothermic reaction. Examples of exothermic reactions are – Rusting or iron, Burning of sugar, Formation of iron pairs, and so on.
Ques. Mention the differencebetween exothermic reaction and endothermic reaction. (3 Marks)
Ans.The major difference between the exothermic reaction and endothermic reaction is that the energy is absorbed from the surrounding into the reaction in the endothermic reaction whereas the energy is released as heat, light, sound, or electricity in the exothermic reaction.
Ques. Define the term water equivalent of the calorimeter and state what will be the PH scale when the strong acids and weak bases react with each other? (3 Marks)
Ans.The water of the calorimeter equivalent is the amount of water that absorbs the same amount of heat that is absorbed by the calorimeter. However, there will be a PH Scale lower than 7 when the strong acids and weak bases react with each other.
Ques. What exactly the enthalpy of the solution means and why is potassium nitrate always used in the powdered form? (3 Marks)
Ans.The enthalpy of the solution is that the solution heat is expressed in KJ/Mol, and when a solution is formed, it will be the amount of the heat energy that is released or get absorbed. Subsequently, the potassium nitrate is always used in the powdered form because the powder gets dissolved easily in the solution.
Ques. Mention three differences between enthalpy and entropy? (3 Marks)
Ans.The difference between enthalpy and entropy are mentioned below –
- Enthalpy is the type of energy whereas entropy is a property.
- Enthalpy is considered as the sum of the internal energy and the flow of energy whereas entropy is the measurement of the randomness of the molecules.
- The enthalpy is denoted by the symbol H whereas the entropy is denoted by the symbol S.
Ques. Describe the relation between enthalpy and entropy. (3 Marks)
Ans.The relation between the formula and the relation between the entropy and enthalpy is that the enthalpy is considered as the central factor in thermodynamics whereas the entropy is the measurement of the thermal energy in the field of thermodynamics.
Ques. What affects the enthalpy of neutralization the most? (3 Marks)
Ans.The heat of the neutralization for the weak acids or weak bases depends on the PH Value and is dependent on the Ph scale values. However, in the absence of mineral added acid or alkali, some amount of heat is required for the complete dissociation.
The heat that evolved during the neutralization will be smaller and the heat of ionization for this reaction is equal to
- -12 + 57.3
- 45.3kj/mol at the temperature of 25o C.
Ques. Is the enthalpy of neutralization of strong acids and strong base is an exothermic reaction or an endothermic reaction? Explain. (3 Marks)
Ans.The enthalpy of neutralization of strong acids and strong base reactions are mostly exothermic because the enthalpy is kept at negative. Subsequently, the heat measurements get performed by carrying out the reactions with a special container known as the calorimeter. Further, the heat is getting off by the neutralization reactions get absorbed by the reaction and calorimeter. Hence, the enthalpy neutralization reactions for the strong acids and strong bases are exothermic.
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