Difference Between Exothermic and Endothermic Reaction

Edited by Diffzy | Updated on: September 02, 2023


Difference Between Exothermic and Endothermic Reaction

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Chemical reactions are a simple way to illustrate the chemical changes we encounter every day. According to the energy transfer between the environment and the system where the reaction is occurring, chemical reactions can be separated into two groups: endothermic reactions and exothermic reactions. Calculating the enthalpy change between reactants and products allows us to determine whether a specific chemical process is endothermic or exothermic. If not, we can track the reaction mixture's temperature change.

Endothermic vs. Exothermic

Endothermic reactions receive energy from the environment, whereas exothermic reactions release energy into the environment. This is the primary distinction between endothermic and exothermic reactions.

Enthalpy of a reaction:

The shift in heat energy that occurs as reactants turn into products is known as a reaction's enthalpy. ΔH is positive if heat is absorbed during the process; if heat is expelled, ΔH is negative.

ΔH value negative → energy released → exothermic reaction

ΔH value positive → energy absorbed → endothermic reaction

Essentials of Endothermic and Exothermic reactions:

Endothermic and exothermic reactions play a major role in our world. They are in charge of all biological functions, including breathing and digestion. They even help with photosynthesis. You can also find endothermic and exothermic reactions out in nature. These reactions involve volcanic eruptions, forest fires, and cloud forms.

Some major fields where these reactions play a crucial role

Refrigeration system:

Research on these exothermic and endothermic reactions has aided in the development of batteries, chemical manufacturing techniques, and refrigeration systems. The list goes on after that. Ammonium nitrate with water can dissolve in particular endothermic processes. This makes cold packs of a quality used in medicine. Gasoline combustion is brought on by exothermic processes.

Manufacturing and Transportation:

Endothermic and exothermic reactions were all a part of manufacturing, transportation, and energy production. Sometimes, these interactions might have a detrimental effect on the quality of the air and water. Sometimes they are risk-free, though. To better illustrate how endothermic and exothermic processes apply to everyday situations, let's look at a few examples.

Difference Between Endothermic and Exothermic in Tabular Form

CharacterizationExothermic reactions or processes release energy into their surroundings, typically in the form of heat or light.Endothermic processes refer to processes that need external energy to proceed, typically in the form of heat. They prefer to cool down their environments because they absorb heat from their surroundings.
EffectSince the total energy of the products is lower than the total energy of the reactants, energy is released in this kind of reaction.Since the products of this sort of reaction have more energy than the reactants, it is not a spontaneous reaction.
Enthalpy changeThe change in enthalpy value is negative for exothermic reactions.The change in enthalpy value is positive for endothermic reactions.
TemperatureTemperature rises as the exothermic reaction progressTemperature lowers with the progress of the endothermic reaction
EnergyEnergy is releasedEnergy is absorbed
Product stabilityStable products are formed in exothermic reactionComparatively less stable products are formed in endothermic reaction
Examplesevaporation, boiling an egg, ice melting, photosynthesis, and splitting of gas moleculesThe formation of ice, the corrosion of iron, the sinking of concrete, and chemical bonding

Endothermic Reaction

Chemical processes known as endothermic reactions take in heat energy from their surroundings. This indicates that external energy must be provided for the beginning and development of an endothermic reaction. The system's temperature drops as a result.

The enthalpy change of the reaction increases as energy is taken in from the outside. Enthalpy is the result of adding a system's internal energy to the energy needed to keep its volume and pressure within its surroundings. The enthalpy of the system is initially equal to the total of the enthalpies of the reactants. Due to the absorption of energy, the products' enthalpy or energy is higher at the end of the endothermic reaction.

A + B → C + D

ΔH = {HC + HD} – {HA + HB}

ΔH = (Hproducts) – (Hreactants) = A positive value


ΔH - Enthalpy change

Hc, Hd - Enthalpies of products C and D

Ha, Hb - Enthalpies of reactant A and B

According to the energy diagram below, in an endothermic reaction, the reactants are at a lower energy level than the products. As a result, the products tend to be less stable than the reactants. Since we are directing the reaction toward more unstable things, the reaction's total H is positive, meaning that energy is being absorbed from the environment.


  • Photosynthesis: As a tree expands, it takes energy from the surroundings to split CO2 and H2O.
  •  Evaporation: As water absorbs heat to transform into gas, sweating helps to cool a person down.
  •   Cooking of egg by absorbing heat from the pan.
  •  Dissolving ammonium chloride solid in water:

                    NH4Cl(s) + H2O(l) + heat → NH4Cl(aq) 

  • Mixing water with potassium chloride:

                     KCl(s) + H2O(l) + heat → KCl(aq)

  • Reacting Ethanoic acid with sodium carbonate:

                    CH3COOH(aq) + Na2CO3(s) + heat → CH3COO–Na+(aq) + H+(aq) + CO32-(aq)

-"Heat" on the left side indicates the absorption of heat

Exothermic Reaction:

Chemical processes known as exothermic reactions discharge heat energy into the environment. This implies that as the chemical reaction develops, energy is released to the outside. The enthalpy of the products is less than the enthalpy of reacting agents because the system's internal energy has been released. The following explanation will help.

Since the internal energy of the reactants has decreased as a result of the energy release, the change in enthalpy now has a negative value. As the exothermic reaction develops, the system's temperature will rise. Therefore, by simply touching the container wall where a chemical reaction is occurring, one can infer whether the process is endothermic or exothermic. A reaction that is exothermic causes the container to warm up.

P + Q → R + S

ΔH = {HR + HS} – {HP + HQ}

ΔH = (Hproducts) – (Hreactants) = A negative value

According to the energy diagram below, in an exothermic reaction, the reactants have a greater energy level than the products. The products are, therefore, more stable than the reactants. Overall, H for the reaction is negative, meaning that heat is generated as a byproduct.


  • Heat is released during the condensation of water vapor into rain.
  •  Chemical processes in concrete emit heat when water is added.
  •  Anything that burns is an exothermic process.
  •  Burning of Hydrogen gas:

                    2H2(g) + O2(g) → 2H2O(l) + heat

  • Combustion of ethanol (complete combustion):

                     CH3CH2OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)

Main Differences Between Exothermic and Endothermic Reactions in Points

  • Exothermic reactions are those that release energy into the environment when they occur, whereas endothermic processes, on the other hand, are those that absorb energy from their surrounding environment in order to carry it out. This is the major distinction between exothermic and endothermic reactions.
  •  In an exothermic process, the change in enthalpy is negative, whereas it is positive in an endothermic reaction.
  •  When an exothermic reaction occurs, energy can be released in any form, such as heat, light, electricity, etc., whereas in an endothermic reaction, energy can only be released in one form of heat.
  •  In an endothermic process, the system's temperature drops over time. For example, the system's temperature drops during evaporation. The system's temperature rises during an exothermic reaction, much like in a nuclear explosion.
  •  As heat is absorbed, endothermic processes will always have an external (from beyond the confines of the system) origin. The environment absorbs the heat from the sun during evaporation. However, the source of an exothermic reaction is the system itself. The instability of the atom in a nuclear explosion is what ignites it.
  •  The spontaneity of the process is another distinction between endothermic and exothermic processes. A spontaneous process doesn't need external energy input. Since heat from the sun or any other source is required to initiate the reaction, evaporation (an endothermic reaction) is not a spontaneous process.
  •  The potential energy of the products in endothermic processes is greater than the potential energy of the reactants. Water vapor has a higher potential energy than water in evaporation. In exothermic reactions, the potential energy of the reactant is higher than the potential energy of the products. Take a nuclear bomb as an example; the reactant's potential energy is substantially higher than the products. (A system is more stable the lower its potential energy).


According to the energy transfer between the system and the environment, chemical reactions are divided into endothermic and exothermic reactions. Endothermic reactions receive energy from the environment, whereas exothermic reactions release energy into the environment. This is the primary distinction between endothermic and exothermic reactions. Calculating the enthalpy change in the reaction allows you to divide every chemical reaction into these two categories.

You now comprehend some of the fundamental ideas relating to endothermic versus exothermic reactions. Learning about exothermic and endothermic reactions will broaden your perspective on the universe. As you can see, these reflexes are crucial to regular operations.

The more we understand these interactions, the simpler it will be to create new, more advanced technology. We can learn, for instance, how exothermic and endothermic reactions can help with the creation of sustainable energy sources. The kind of remedies that reduce harmful environmental effects.


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"Difference Between Exothermic and Endothermic Reaction." Diffzy.com, 2023. Sun. 24 Sep. 2023. <https://www.diffzy.com/article/difference-between-exothermic-and-endothermic-reaction>.

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