11 Endergonic Reaction Example: Detailed Explanations

In this article, “endergonic reaction example, different types of examples on endergonic reaction with detailed explanations are discussed below.

The examples are-

  1. Photosynthesis
  2. Protein Synthesis
  3. Dissolving Potassium Chloride in Water
  4. Na+/K+ Pump
  5. Melting of Ice into Liquid Water
  6. Fatty Acid Synthesis
  7. Chemosynthesis
  8. DNA/RNA Synthesis
  9. Electrolysis of Water
  10. Formation of Nitrogen Monoxide
  11. Formation of Ozone
  12. Mixing of Baking Soda and Citric Acid in Water

What is an Endergonic Reaction?

Endergonic reaction is known as nonspontaneous reaction in thermodynamics or physical chemistry.  Change of Gibbs free energy for an endergonic reaction is always positive (∆G>0). Due to positive free energy change, an external driving force is required to make proceed the reaction into forward direction.

Characteristics of endergonic reaction is described below-

  • The bonds are formed in the product side are relatively weaker than those bonds broken in the reactant side.
  • Change of entropy of an endergonic reaction is negative (∆S<0).
  • Temperature plays an important role for endergonic reaction. Increasing temperature in surroundings drives the endergonic reaction towards an endothermic reaction (∆H>0)
endergonic reaction example
Energy Diagram of an Endergonic Reaction. Image Credit: Wikimedia Commons


Photosynthesis is a chemical process executed by green plants having chlorophyll to convert light energy into chemical energy. It is one of the most important examples of endergonic reaction as sunlight (energy) is absorbed for the reduction process of carbon dioxide to form oxygen and glucose molecules.  This absorbed energy is stored in different chemical bonds of plants. This is a nonspontaneous reaction as well as endothermic reaction having (H>0 and ∆G>0).

Balanced chemical reactions involved in photosynthesis reaction is-

6CO2 + 6H2O C6H12O6 + 6O2

Image Credit: Wikimedia Commons

Protein Synthesis

Protein is synthesised due to the attachment of amino acids by condensation reaction. Peptide bond is formed between two amino acids and the formation of peptide bond needs high amount of energy. This energy is supplied due to the hydrolysis of ATP (adenosine triphosphate) to ADP (adenosine diphosphate). Thus, Gibbs free energy change for this anabolism us positive and this leads the protein synthesis to an endergonic reaction.

To know more please check: 5+ Intermolecular Hydrogen Bond Examples: Detailed Explanations.

Dissolving Potassium Chloride in Water

Potassium chloride is an ionic salt and a strong electrostatic attraction is present in between the two oppositely charged ions (K+ and Cl). To dissolve KCl in water this electrostatic attraction should be eliminated. This elimination of strong electrostatic attraction needs a high amount of energy. So, energy must be supplied from surroundings or any other source for this dissolution or hydration process.

KCl (s) → K+ (aq) + Cl (aq)

Na+/K+ Pump

Sodium-potassium pump works in active transport system (∆G>0). The significance of this ion pump is to maintain the concentration gradient of Na+ and K+ across the cell membrane.  For a typical cell: [Na+]outside/ [Na+]inside =15 and [K+]inside/[K+]outside = 25, the high concentration of K+ ion inside the cell is required for some important biological process occurring within the cells.

Na+ and K+-ATP-ase enzyme helps to drive the ion pump. The energy needed for the pump is supplied by the hydrolysis of ATP to ADP.

Sodium-Potassium Ion Pump.
Image Credit: Wikimedia Commons

  To know more please follow: 12+ Exothermic Reaction Examples: Detailed Explanations

Melting of Ice into Liquid Water

Melting of ice into liquid water is also an energy requiring (endothermic) as well as endergonic process. Heat energy must be supplied to liquify ice. This energy is needed to overcome the strong attraction force present in the solid state. The energy equals to latent heat is required to change ice at 273K to water at 273K.

Fatty Acid Synthesis

The reductive synthesis of fatty acid leads to convert acetyl-CoA and NADPH to fatty acid in cell cytoplasm. This acetyl-CoA is derived from carbohydrate through glycolysis. Like the other biological process ATP is the source of the metabolic energy.


Chemosynthesis is an endergonic process which is defined the formation of glucose molecule by different types of bacteria using chemical species used as the energy source. Sunlight is not used as energy source because chemosynthesis occurs in deep sea where sunlight cannot reach. During this process, bacteria use the energy stored in the chemical bonds of mainly hydrogen sulfide and methane using water and carbon dioxide and form glucose molecule.

DNA/RNA Synthesis

DNA (deoxyribo nucleic acid) and RNA (ribo nucleic acid) are macromolecules formed by the nucleotides and contain deoxyribose or ribose sugar, phosphate and nitrogen base (purine and pyrimidine). Nucleotide units are linked by covalent bonds hydrogen bonds with each other. Each nucleotide is joined through the phosphate group by forming covalent bonds. This is a high energy requiring process and free energy change is highly positive for this process.

DNA Synthesis.
Image Credit: Wikimedia Commons

To know more please go through: 12+ Decomposition Reaction Example: Detailed Explanations

Electrolysis of Water

This is obviously an endergonic reaction example and is carried out in presence of electric energy. This energy helps to decompose water into its constituent ions, hydrogen ion and hydroxyl ion. Oxygen in anode and hydrogen gas in cathode is produced in this electrolysis reaction. Pure water cannot be electrolysed. Thus, a small amount of acid is added with water and apply electric energy on it. The amount of hydrogen produced in cathode is twice of the amount of oxygen in anode.

Reduction in cathode: 2H+ (aq) +2e H2 (g)                          Oxidation in anode: 2OH (aq) (½) O2 (g) + H2O (l) + 2e                     

Net balanced equation:

2H2O 2H2 + O2

Formation of Nitrogen Monoxide

When nitrogen and oxygen is reacted to form nitrogen monoxide approximately 181KJ energy is absorbed during the progress of reaction. Thus. Formation of nitrogen monoxide is definitely an endothermic reaction. But it is also an endergonic reaction because the free energy change during this reaction is positive. So, it is a nonspontaneous reaction. To run this formation extra energy must be supplied from any external energy source.

N2 (g) + O2 (g) 2NO

Formation of Ozone

Formation of ozone from molecular oxygen requires a high amount of energy to run the process. Ultraviolet ray comes from sun is the source of energy and this reaction proceeds through free radical pathway. Change of standard enthalpy of formation is almost 143KJ.

3O2 (g) 2O3 (g)

To know more please read: 11+ First Order Reaction Example: Detailed Explanations

Mixing of Baking Soda and Citric Acid in Water

When citric acid from lemon like fruit comes in contact with baking soda in water, carbon dioxide is formed. This carbon dioxide is fizzing and bubbling in the two ingredients. At the first step bicarbonate (HCO3) ion is formed, later it decomposes and form carbon dioxide.

H+ + HCO3 H2CO3 H2O + CO2

This is an endergonic reaction as energy is required to run this reaction.

Frequently Asked Questions (FAQ)

What is the difference between an endergonic and an exergonic reaction?

Exergonic ReactionEndergonic Reaction
Change of Gibbs free energy for an exergonic reaction is negative. Thus, it is an example of spontaneous reaction (∆G<0).Change of Gibbs free energy for an endergonic reaction is positive (∆G>0). Thus, it is an example of nonspontaneous reaction.
Change of enthalpy for this reaction is negative (∆H<0).Change of enthalpy for this reaction is positive (∆H>0).
For an exergonic reaction change of entropy is positive (∆S>0).For an endergonic reaction change of entropy is negative (∆S<0).

What is the effect of temperature on an endergonic reaction?

Answer:  Increasing temperature disfavour endergonic reaction. Temperature must be low to proceed the endergonic reaction towards forward direction.

Dos endergonic reaction take place slowly?

Answer: Endergonic reaction takes place in slow process with respect to exergonic reaction as the change of Gibbs free energy is positive for an endergonic reaction.

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