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Thermodynamics and Thermochemistry

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Last updated date: 29th Feb 2024
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Thermodynamics and Thermochemistry: An Introduction

Everything around us requires reaction to form the end product. There is always an initiator in the reaction which occurs in this universe. The universe consists of the two things - System and Surroundings. The System can be defined as the place where the reaction is happening or everything else is considered as the surroundings. The reaction can happen naturally or can be artificially done. There is always an initiator or catalyst which begins the reaction or helps the reaction to run. The catalyst can be anything which helps the reaction, it can be heat, light, water, electricity, or some bacteria. In this article, we will discuss the heat as the initiator or catalyst in the chemical reaction.

Thermodynamics and thermochemistry deal with the rate of flow of the heat in the chemical reaction or the chemical reaction which is produced by the presence of heat.


What is Thermodynamics?

In Thermodynamics, thermo means heat and dynamics means rate which means the rate of flow of the heat. The thermodynamics came into existence to increase the efficiency of the heat engine, to convert all the energy into work and produce less heat as the product in the engine because of wastage of energy and wear-tear in the engine.


Thermodynamics can be defined as the transformation of one energy into the other energy. In this article, we will talk about the transformation of heat energy into some useful energy to do work. Thermodynamics can be defined by the flow of heat which can be described by the internal energy, entropy, and enthalpy.


Thermochemistry Equation

Thermochemical equation is the equation which describes the change in the heat during the reaction.

Here, exothermic reaction can be defined as the balanced chemical reaction which occurs due to the heat.

\[C{H_4} + {\rm{ }}{O_2} \to C{O_2} + {\rm{ }}{H_2}O{\rm{ }} + {\rm{ }}Heat\]

In the above reaction, the methane reacts with oxygen gas to provide the carbon dioxide, water molecule, and heat as bi-products.

Endothermic reaction can be defined as the balanced chemical reaction which gives heat as a product.

\[C\left( s \right){\rm{ }} + {\rm{ }}{H_2}O\left( l \right){\rm{ + Heat}} \to C{O}\left( g \right){\rm{ }} + {\rm{ }}{H_2}\left( g \right)\]

In the above reaction, the carbon reacts with water molecules in the presence of heat to provide the carbon monoxide, hydrogen gas molecule.

What is Thermochemistry?

In thermochemistry, thermos means heat and chemistry means chemical reaction which means the heat is responsible for the chemical reaction to occur. The French chemist Antoine Laurent Lavoisier and Pierre Simon de Laplace made this different field of chemistry in the year 1780. They study about the reaction happening around as most of the reaction takes place by the absorption of the heat or releasing heat during the reaction or as the end product.

Thermochemistry is the branch of chemistry which describes the changes occurring in the chemical reaction due to the presence of heat.

According to the flow of heat, the chemical reaction can be defined as the exothermic and endothermic reaction. Exothermic reactions are those reactions which occur when the heat is provided to the reactants whereas the endothermic reactions are those which releases heat energy after the chemical reaction occurs.


Laws of Thermochemistry

Thermochemistry can be defined as the change in the heat of the chemical reaction. Here, change in heat can be defined by the equations.

Thermochemistry can follow the law:

  • Change in the heat is directly proportional to how the moles of substance reacts to form the balanced moles of product.

  • Magnitude of change in heat in the reaction is equal to the opposite of the sign of the reverse reaction.

  • The change in heat in the reaction can be defined by Hess's law which states that the change in heat is equal to the resultant reaction to the magnitude of the change in heat of the small reaction involved.

$\text{Resultant} \ \text{reaction} \ = \ \text{Reaction} \ 1 + \text{Reaction} \ 2$

$\Delta \ H_R \ = \Delta H_1 + \Delta H_2$


Difference Between Thermodynamics and Thermochemistry

Both thermodynamics and thermochemistry are the study of heat in the reaction. There are some differences in thermodynamics and thermochemistry because of the purpose. Thermodynamics tells about the rate of the flow of heat whereas thermochemistry can be defined as the type of chemical reaction which happens due to the absorption heat and releasing heat.


Key Features

  • Chemical reaction can be defined as the reactants react to form products with the help of the initiator or catalysts.

  • Thermodynamics can be defined as the transformation of one energy into the other energy.

  • Thermochemistry is the branch of chemistry which describes the changes occurring in the chemical reaction due to the presence of heat.

  • Exothermic reactions are those reactions which occur when the heat is provided to the reactants whereas the endothermic reactions are those which releases heat energy after the chemical reaction occurs.

  • Hess’s Law states that the change in heat is equal to the resultant reaction to the magnitude of the change in heat of the small reaction involved.

Interesting Facts

  • In cold countries, the thermometer is more filled with alcohol than mercury because alcohol has a lower freezing point than mercury.

  • The only perfect body which is called isolated is our Universe.

  • The energy absorbed and released by any object can be determined by thermochemistry.

Competitive Exams after 12th Science

FAQs on Thermodynamics and Thermochemistry

1. What do you mean by thermodynamics?

The transformation of heat energy into some useful energy to do work. Thermodynamics can be defined by the flow of heat.

2. What do you mean by the exothermic and endothermic reaction? 

Exothermic reactions are those reactions which occur when the heat is provided to the reactants whereas the endothermic reactions are those which release heat energy after the chemical reaction occurs. 

3. What is Hess’s law?

Hess’s law states that the change in heat is equal to the resultant reaction to the magnitude of the change in heat of the small reaction involved.

$Resultant \ reaction \ = \ Reaction \ 1 + Reaction \ 2$

$\Delta \ H_R \ = \Delta H_1 + \Delta H_2$