What are exergonic and endergonic reactions, and what are some examples of them?

An exergonic reaction is one in which ##ΔG## increases, and an endergonic process is one in which ##ΔG## decreases.

##ΔG## is the energy that is available to do work.

You can read about exergonic and endergonic reactions at

http://socratic.org/questions/is-exergonic-the-same-as-endothermic-or-exothermic?source=search

An example of an exergonic reaction that occurs in our body is cellular respiration. The equation for the oxidation of glucose to carbon dioxide and water is:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O; ##ΔG## = -3012 kJ

This reaction releases energy that the cell uses for its activities.

The above value of ##ΔG## is for the conditions found within a cell. The tabulated value of ##ΔG^°## = -2870 kJ refers to standard conditions (1 atm, 25 °C).

An example of an endergonic reaction in the cell is the formation of a peptide bond.

NH₂CHRCOOH + NH₂CHRCOOH → NH₂CHRCO-NHCHRCOOH + H2O; ##ΔG## ≈ +8 - 12 kJ

Amino acids join to make dipeptides, and the process continues as large protein molecules are built up.