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Heat of Formation

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An Introduction to Heat of Formation

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In the field of Physics as well as Chemistry, the influence of compounds and mole is hugely significant. The reason behind such significance is that through the study and analysis of one mole of any and every compound, a broader, more generalized idea about the compound, or even similar compounds can be deduced and inferred. Therefore, the answer to “What is enthalpy of formation” is- it is the heat amount that is absorbed or even evolved during the process of formation of one mole of any compound from the constituent elements of the compound. 


Standard Enthalpy of Formation 

As has been mentioned before, the process of heat absorption or heat evolution during the formation of a compound’s mole is called the enthalpy of formation. The term “enthalpy” is used to refer to the internal energy of a thermodynamic mechanism or system in its totality, along with the combined product of the system’s volume as well as its pressure. 

Therefore, as it can be understood, the standard heat of the formation of a mole of a compound is the combined heat of the sum of its internal energy and the product of volume and pressure. Since assumptions and deductions are necessary for the formation of any and every mole, it has been observed that generally, a compound initiates its formation at 77- degree Fahrenheit temperature, where the necessary pressure is of one atmosphere. Therefore, this is considered the standardised amount of heat necessary for the formation of a mole of a compound.  


Define Standard Enthalpy of Formation 

Since the law of energy conservation states that the heat that is transferred to the system is equal to the change of the system’s internal energy, the amount of heat that is provided externally to material for it to change its own phase is known as enthalpy, where the heat necessary for converting a liquid material to its gaseous form is called the enthalpy of vaporization. Since the differences in the phases of materials are also concerning the standard enthalpy of formation, it is necessary to keep in mind the various phases that materials consist in. 

As is known to almost all of us, there are three primary phases for a material. The three fundamental states of matter that are the most prevalent in our day to day lives are- Solid, Liquid and Gas or Vapour. The reason why these three are the most prevalent forms of thermodynamic phases is that they are the three phases that we are the most accustomed with. We have seen how water exists in its liquid form in lakes and oceans, whereas it exists in its solid form in icecaps and also, how it exists in its gaseous form when water is boiled on the stove. Therefore, with the differences in the phases of a material, the respective heat of formation also gets altered. 


What is Heat of Formation? 

As has been mentioned earlier, the standard enthalpy of formation is used to refer to the heat amount that is absorbed or even, evolved during the process of formation of one mole of any compound from the constituent elements of the compound. Thus, as is to be understood, in order to deduce the amount of heat, whether evolved or absorbed, there is a standard formula which can be utilised to infer the amount. 


The Heat of Formation Formula 

As has been discussed thus far, the standard heat of the formation of a mole of a compound is the combined heat of the sum of its internal energy and the product of volume and pressure. Since assumptions and deductions are necessary for the formation of any and every mole, it has been observed that generally, a compound initiates its formation at 77- degree Fahrenheit temperature, where the necessary pressure is of one atmosphere. 

So, with regards to the question of “What is standard heat of formation?”, it can be answered by stating the formula of the same. The formula is thereby, followed- 

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Did You Know? 

  • For the calculation of heat absorbed or even evolved during any chemical reaction, the heats of that step’s formation and/ or combustion are to be summed up. 

  • In order to calculate the heat absorbed or heat evolved for a reaction, the theory that is used is known as Hess's Law of Heat Summation. 

  • The name for the law of Heat Summation belongs to Germain Henri Hess, who first proposed the law in Russia in 1840. 

FAQ (Frequently Asked Questions)

1. What is the Enthalpy of the Formation of a Mole of a Compound in Thermodynamics? 

Ans: The term “enthalpy” is used to refer to the internal energy of a thermodynamic mechanism or system in its totality, along with the combined product of the system’s volume as well as its pressure. The standardised amount of heat of formation of a mole of compound is the combined heat of the sum of its internal energy and the product of volume and pressure. Since through the study and analysis of one mole of any and every compound, a broader, more generalized idea about the compound, or even similar compounds can be deduced and inferred, the usage of enthalpy of formation for the mole of a compound has become so prevalent. 

2. How does the Phase of a Material Affect the Heat of Formation of Mole for that Material? 

Ans: Since there are three primary phases for a material- solid, liquid and gas or vapour, the enthalpy of materials correlate differently with these three prevalent phases. The reason why these three are the most prevalent forms of thermodynamic phases is that they are the three phases that we are the most accustomed to. We have seen how water exists in its liquid form in lakes and oceans, whereas it exists in its solid form in icecaps and also, how it exists in its gaseous form when water is boiled on the stove. Therefore, with the differences in the phases of a material, the respective heat of formation also gets altered.