Introduction to Enthalpy of Reaction

Basics of Enthalpy of Reaction

Enthalpy of Reaction, or heat of reaction, represents the total energy change in a chemical reaction.
It is generally represented as ΔH.
Enthalpy of reaction is measured in joules or more commonly in kilojoules.
During a chemical reaction, energy can either be absorbed from or released to the surroundings. This energy is the enthalpy of the reaction.
A chemical reaction in which energy is absorbed from the surroundings is called an endothermic reaction and has a positive enthalpy.
A reaction in which energy is released to the surroundings is an exothermic reaction and has a negative enthalpy.

Enthalpy of reaction is calculated by subtracting the sum of the enthalpies of the reactants from the sum of the enthalpies of the products.
It uses a mathematical relation: ΔH = Σ ΔH(products) - Σ ΔH(reactants).
In this equation, Σ (the Greek letter Sigma) represents the sum of.

The nature of reactants plays a crucial role as different substances have different capabilities to absorb or release energy.
The physical state of reactants and products directly influence the enthalpy of reaction as changing the state of a substance requires or releases energy.
Pressure and temperature of the surroundings also affect the enthalpy of reaction.

Enthalpy of reaction is fundamental in thermodynamics for understanding the energy transfer during a chemical reaction.
These energy changes can affect the speed and direction of a reaction.
By understanding and predicting these energy changes, we can design chemical reactions for maximum efficiency and safety.
The knowledge of enthalpies can help us know whether a particular reaction will occur naturally (spontaneously) or requires an outside energy source to proceed.