Question

All of the following statements about exergonic reactions are true EXCEPT (A) The products contain less energy than the reactants. (B) The energy released can be used to perform work. (C) They usually occur instantaneously. (D) They release energy in the form of ATP or heat. (E) They require energy input before the reaction can proceed.

Short answer

The statement 'Exergonic reactions usually occur instantaneously'(C) is not true about exergonic reactions.

Step-by-step solution

Evaluate each statement individually

Look at each statement individually to determine if it describes an exergonic reaction.

Understand exergonic reactions

Exergonic reactions are characterized by a release of energy (usually in the form of ATP or heat). The products of these reactions contain less energy than the reactants, meaning that they release energy, which can then be employed in doing work. They also require a certain amount of energy input to start, known as the activation energy.

Identify the wrong statement

Statement (C) indicates that exergonic reactions usually occur instantaneously. This is however incorrect. Regardless of being exergonic, all reactions require an activation energy to start and do not happen instantaneously.

Key concepts

Activation Energy

Activation energy is the initial push that gets a chemical reaction started. Imagine trying to roll a boulder up a hill; you need to exert force initially to overcome gravity and get the boulder moving. Similarly, every chemical reaction needs a certain amount of energy to initiate the process.
This energy is called the activation energy and is necessary to break the bonds of reactants so they can form products.

• In exergonic reactions, this energy input is required despite the reaction eventually releasing more energy than it consumes.
• Though an exergonic reaction has a net loss in energy, the activation barrier must still be overcome for the reaction to proceed.
• Without the needed activation energy, reactions wouldn’t spontaneously occur because they have no initial force to start the process.

The amount of activation energy influences how quickly a reaction can go. Higher activation energy often slows the reaction rate since more energy is needed to start the process.

Energy Release

In exergonic reactions, energy is released because the products are more stable than the reactants. This means that they contain less energy overall than the reactants did initially.
During these reactions, the difference in energy between reactants and products is released, usually as heat or ATP.

• The energy given off can be used by the cell to perform various functions, like moving substances across cell membranes or catalyzing other reactions.
• The energy release is what makes exergonic reactions favorable and often spontaneous once initiated.
• This release is crucial for biological processes, as it provides the necessary energy cells need to maintain homeostasis, grow, and reproduce.

Depending on the context, this energy can drive not just work at the cellular level but also be used in mechanical processes, such as muscle contraction.

Reaction Kinetics

Reaction kinetics is the study of the rates of chemical reactions and how different conditions affect these rates.
For exergonic reactions, reaction kinetics helps us understand why reactions don't happen instantly despite them being energetically favorable.

• The presence of enzymes significantly influences reaction kinetics, as they can lower the activation energy required, speeding up the reaction.
• Temperature, concentration of reactants, and catalysts (such as enzymes) all play important roles in how quickly reactions proceed.
• Understanding reaction kinetics is essential for controlling and optimizing these reactions, such as in metabolic pathways where the precise timing and rate of reactions are crucial for proper cellular function.

In a biological system, fine-tuning these factors ensures that metabolic processes occur smoothly and efficiently, conserving energy where possible.

ATP

ATP, short for adenosine triphosphate, is often referred to as the energy currency of the cell.
It stores and provides energy whenever it's required for cellular processes.

• During exergonic reactions, energy released can be used to convert ADP (adenosine diphosphate) back into ATP by adding a phosphate group.
• This reconversion of ATP is fundamental because cells use ATP as a direct energy source for a multitude of activities, from mechanical work to chemical synthesis.
• Cells maintain a balance of ATP production and utilization, using exergonic reactions to continuously replenish this vital molecule.

The ability of ATP to grant immediate energy helps cells perform swift actions, ensuring they can respond to changes and demands efficiently.