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An endothermic vs exothermic comparison is a distinction between two fundamental energy changes that occur in nature. Everything that happens in nature is some form of an energy change and depending on the direction of flow of energy, that change or reaction may be classified as an endothermic or exothermic reaction. Let us understand the difference between endothermic and exothermic reactions.

Endothermic Vs Exothermic Reactions: Comparison

Every change that you see in a natural system involves the transaction of energy. Thermodynamics is the branch of physics devoted to studying these changes. A combination of physics and chemistry principles are required to study thermodynamics of chemical reactions. To understand how some chemical reactions occur or why some do not occur, one needs to know the concepts of endothermic and exothermic reactions. Often, setting up the energy transaction account or energetics for a particular reaction, can tell you about the possibility or probability of that reaction occurring spontaneously. It all depends on knowing how much energy needs to be released or absorbed for the reaction to occur. Let us first define what we mean by endothermic and exothermic reactions.

Endothermic Vs Exothermic: Fundamental Differences

Let us define both these different types of reactions first. An endothermic reaction is any chemical or physical reaction that requires the input of energy for its successful execution. ‘Endo’ means inside ‘thermic’ stands for heat. A chemical reaction that involves breaking of bonds requires external energy input from its surroundings. That is why reactions that involve breaking of stable bonds in molecules are endothermic reactions. The energy absorbed is mostly in the form of heat.

As opposed to this, an exothermic reaction involves release of energy during its successful execution. ‘Exo’ stands for outside while ‘thermic’ is again for heat. This release of energy is often in the form of heat, which is spontaneously released. The formation of a new bond is a low energy state and therefore when new stable bonds are formed between atoms, energy is released. That is why most bond forming reactions are exothermic. The release of energy may occur in various forms. It may occur in the form of photons being released or heat energy being released into the surroundings.

Endothermic Vs Exothermic: Enthalpy, Internal Energy & Entropy Change

There are three thermodynamic potentials that need to be taken into consideration while evaluating the outcome of a reaction. These potentials are enthalpy, internal energy and entropy. Enthalpy is the quantity which determines the amount of mechanical (pressure-volume) work that a system is capable of. Internal energy is the sum total of potential (Bond Energy), as well as kinetic energy (vibrational, rotational, translational) of the system. Entropy is a measure of lost energy and disorder in a system. Let us see what changes occur in these potentials during endothermic and exothermic reactions.

During an endothermic reaction occurring at constant pressure, the enthalpy increases. If the endothermic reaction occurs at constant volume, internal energy increases. Entropy can never decrease overall. Though it may seem to locally decrease during an endothermic reaction, it always increases globally.

During an exothermic reaction, entropy increases substantially due to the heat released. Enthalpy decreases when the reaction occurs at constant pressure, while internal energy decreases when the reaction occurs at constant volume. You may also want to read on the different types of chemical reactions and chemical reactions in everyday life.

Endothermic Vs Exothermic: Examples in Nature

Let us have a look at some exothermic and endothermic reaction examples found in nature. First we consider exothermic ones. Here are some that we get to see in everyday life.

• Water vapor or fog condensing as a dew drop is an exothermic reaction releasing heat in the process.
• The rusting of iron is an exothermic and spontaneous reaction.
• Nuclear fission is an exothermic reaction which powers the nuclear reactors of today.
• Any type of spontaneous combustion including burning of wood are exothermic reactions that generate heat.

Endothermic reactions are less spontaneous, as they require an external input of energy. Here are some examples of exothermic reactions, we see in everyday life.

• Photosynthesis is an endothermic reaction that occurs in plants, as they require external energy input in the form of sunlight or solar photons.
• Melting of ice cubes is another endothermic process which requires external heat input to break the bonds in crystal structure of ice.
• Cooking of an egg is an endothermic reaction, as it requires external heat input.
• Evaporation of water is an example of endothermic reaction as it requires heat input.

Hope this endothermic vs exothermic comparison has cleared all your doubts about these two fundamental types of energy changes. Nature operates through a principle of least action and therefore low energy states are more preferable than high energy states, as they are more stable. That is why, most natural reactions are spontaneous and exothermic, while most artificial reactions are endothermic.

1 Comment

Onwe Christian Ikenna

This is absolutely commendable as it entails the vitality in chemistry pertaining to endothermic and exothermic reactions.However, i would more euphoric if the factors affecting these reactions are dealt with in a clear and understandable way. Once more, it’s a nice work.