Think of it as the “energy currency” of the cell. If a cell needs to spend energy to accomplish a task, the ATP molecule splits off one of its three phosphates, becoming ADP (Adenosine di-phosphate) + phosphate. The energy holding that phosphate molecule is now released and available to do work for the cell.

When a phosphate is removed, the energy that is released can be used for cellular work and chemical synthesis. Adenosine triphosphate (ATP) is considered by biologists to be the energy currency of life.

What happens when a phosphate group is removed from an ATP molecule? When a phosphate group is removed from ATP, energy is released and ADP results. ATP is converted into ADP and a phosphate group.

When one of the phosphates is removed, the energy stored in the covalent bond is released, and the cell is able to do work.

ATP (adenosine triphosphate) has three phosphate groups that can be removed by hydrolysis to form ADP (adenosine diphosphate) or AMP (adenosine monophosphate). The negative charges on the phosphate group naturally repel each other, requiring energy to bond them together and releasing energy when these bonds are broken.

ATP provides the energy for both energy-consuming endergonic reactions and energy-releasing exergonic reactions, which require a small input of activation energy. When the chemical bonds within ATP are broken, energy is released and can be harnessed for cellular work.

Exergonic reactions can be coupled to endergonic reactions. Oxidation-reduction (redox) reactions are examples of the coupling of exergonic and endergonic reactions. Enzymes often act by coupling an endergonic reaction to the exergonic hydrolysis of ATP.

All redox reactions are coupled reactions, since an oxidation reaction is coupled to a reduction reaction. The reduction of acetaldehyde is coupled to the oxidation of NADH to NAD+, which is an exergonic reaction. The oxidized NAD+ has a lower energy level than NADH.

For those reasons, any large molecules we digest can be broken down to smaller molecules in exergonic reactions (these smaller molecules then enter cells, where further reactions could be exergonic or endergonic). Oxidation is usually considered exergonic reaction as it involves release of energy.

If a molecule is oxidized, does it gain or lose energy? Oxidation occurs when a molecule loses an electron or increases its oxidation state. When a molecule is oxidized, it loses energy.

Non-standard conditions and chemical equilibrium The standard free energy change (∆Gº’) of a chemical reaction is the amount of energy released in the conversion of reactants to products under standard conditions.

Oxidation is the loss of electrons, gain of oxygen or loss of hydrogen. Reduction is the gain of electrons, loss of oxygen or gain or hydrogen.

Oxidation is a reaction that removes an electron from a substance, reduction is a reaction that adds electrons to a substance.

The iron metal is oxidized to form the iron oxide known as rust. Electrochemical reactions are great examples of oxidation reactions. When a copper wire is placed into a solution that contains silver ions, electrons are transferred from the copper metal to the silver ions. The copper metal is oxidized.

Identifying Reaction Types A redox reaction must involve a change in oxidation number for two of the elements involved in the reaction. The oxidized element increases in oxidation number, while the reduced element decreases in oxidation number.

Oxidation is the loss of electrons. Reduction is the gain of electrons. Oxidation and reduction always occur together, even though they can be written as separate chemical equations.

The wood burning loses electrons to the oxygen in the atmosphere.