Enthalpy of Reaction

Introduction 

While studying chemistry or dealing with chemical reactions, a brief understanding of the enthalpy of reaction and the standard enthalpy is crucial. It enables the calculation of pressure and temperature. It is also important to calculate the heating amount and cooling required when the reaction takes place on a large scale, such as when calcium carbonate, ammonia, oxygen etc., are produced at a mass scale. This article examines the study material on the enthalpy of reaction. 

What is Enthalpy? 

Enthalpy can be defined as the energy measurement in the thermodynamic system. The Enthalpy quality is the same as the total content of heat of the system, which is equivalent to the internal energy of the system along with the product of pressure and volume. Enthalpy is extremely important as it gives a clear understanding of the amount of heat present in the system. Heat is critical as it promotes valuable work. 

Enthalpy of Reaction 

We already know the energy change is the same as the sum of work done and heat produced. Work completed through the gas is called pressure-volume, also known as the PV work. For example, when there is a chemical reaction that produces only gas, such as dissolving a copper piece in the nitric acid. Here is the chemical reaction – 

Cu(s) + 4 HNO3 (aq) → Cu (NO3)2 (aq) + 2H2O(l) + 2NO2(g) 

If the reaction takes place in the closed system, which is managed at constant pressure, the piston will start to increase as a result and give rise to nitrogen dioxide gas. The total PV work can be identified after multiplying all external pressure with the volume change caused by the movement of the piston. 

w=−PΔW

The sign placed before the PV shows that the system starts to lose energy as soon as the volume automatically increases. Imagine the volume is increasing at constant pressure (ΔV>0), the work completed by the system is (-) or negative, which means that the system has lost energy. However, if the volume starts to decrease (ΔV<0), the work completed is (+) or positive, which indicates the work done by the surroundings. 

Enthalpy Change 

The Enthalpy Change can be described as the enthalpy of the formation, which is being determined for several substances. When talking about any chemical reaction, several chemical changes occur in a reactant that further combines for giving products. Here is the equation for the same: 

Reactants → Products 

If such a reaction occurs, the Enthalpy change is represented as ΔrH and is referred to as reaction enthalpy. To calculate the reaction enthalpy, subtract the sum of enthalpies of all the reactants from the products.

It can be written as: 

ΔtH = sum of products’ enthalpies – Sum of the reactants’ enthalpies.

Reaction Standard Enthalpy 

Since we know that the enthalpy of all reactions is determined by the physical conditions of nearby places, including the pressure, temperature, and others. To clearly state the Standard enthalpy of reaction, it can be calculated easily when all the components taking part in the reaction, i.e., the products and the reactants, are in their standard form. 

Introduction of The Zeroth law of Thermodynamics

The Zeroth law of thermodynamics can be defined as when the body ‘X’ along with another body ‘Y’ is in thermal equilibrium with the body ‘Z’, then body ‘Y’ and ‘Z’ will also be in thermal equilibrium with one another. The Zeroth law of thermodynamics is majorly dependent on temperature measurement. However, there are several different ways to state the temperature measurement. 

According to the Zeroth law of thermodynamics, the temperature is worth measuring as it states if the heat will be transferred between different objects. This is exactly how objects tend to interact with one another. Whether two objects are in physical contact with each other or not, the heat can still travel between those. 

Conclusion 

The enthalpy of reaction, also known as the heat of change, is a crucial topic of Chemistry. This article discussed the enthalpy and enthalpy of reaction in length. We also talked about enthalpy change and reaction standard enthalpy. In the end, we introduced the zeroth law of thermodynamics. This study material on the enthalpy of reaction must have helped attain a greater understanding of the enthalpy of reaction and other related topics.