logo

Animation: Exergonic and Endergonic Reactions

by Pearson
9 views
Was this helpful ?
0
Cells contain many different molecules that can engage in a variety of chemical reactions. When molecules react, for example when they collide and exchange parts, their atoms and bonds are rearranged. Reactants are rearranged to form products. Reactant and product molecules store potential energy in the arrangements of their atoms and bonds. Chemical reactions involve changes in bonding and changes in energy. We can plot potential energy on a graph and compare the potential energy of reactants and products. Using these molecules as an example, we can imagine two chemical reactions. Molecules AB and CD react to form molecules AC and BD, or vice versa. Among the two reactions shown, the reaction shown in the left graph has products with less potential energy than the reactants. In this reaction, energy is released to the surroundings as the reactants are rearranged to form products. The potential energy of the molecules drops. In the other reaction, the product molecules have more potential energy than the reactants. The reactants must absorb energy from their surroundings for this reaction to occur. Chemical reactions that release energy are called exergonic reactions. You might call exergonic reactions downhill reactions. Other reactions, called endergonic reactions, are uphill changes; they absorb energy from their surroundings. Exergonic reactions occur spontaneously or, that is, without a net addition of energy. The potential energy of the molecules decreases. It is easier for a cell to carry out a reaction that does not need additional energy input. A downhill change is easier than an uphill change. Endergonic reactions do not occur spontaneously. It is harder for a cell to carry out a reaction that needs additional energy input. An uphill change is harder than a downhill change.
Cells contain many different molecules that can engage in a variety of chemical reactions. When molecules react, for example when they collide and exchange parts, their atoms and bonds are rearranged. Reactants are rearranged to form products. Reactant and product molecules store potential energy in the arrangements of their atoms and bonds. Chemical reactions involve changes in bonding and changes in energy. We can plot potential energy on a graph and compare the potential energy of reactants and products. Using these molecules as an example, we can imagine two chemical reactions. Molecules AB and CD react to form molecules AC and BD, or vice versa. Among the two reactions shown, the reaction shown in the left graph has products with less potential energy than the reactants. In this reaction, energy is released to the surroundings as the reactants are rearranged to form products. The potential energy of the molecules drops. In the other reaction, the product molecules have more potential energy than the reactants. The reactants must absorb energy from their surroundings for this reaction to occur. Chemical reactions that release energy are called exergonic reactions. You might call exergonic reactions downhill reactions. Other reactions, called endergonic reactions, are uphill changes; they absorb energy from their surroundings. Exergonic reactions occur spontaneously or, that is, without a net addition of energy. The potential energy of the molecules decreases. It is easier for a cell to carry out a reaction that does not need additional energy input. A downhill change is easier than an uphill change. Endergonic reactions do not occur spontaneously. It is harder for a cell to carry out a reaction that needs additional energy input. An uphill change is harder than a downhill change.