Question

What do the following indicators tell you about whether a reaction can proceed as written? (a) The standard free-energy change is positive. (b) The free-energy change is positive. (c) The reaction is exergonic.

Short answer

(a) Non-spontaneous (b) Non-spontaneous (c) Spontaneous

Step-by-step solution

Understanding Standard Free-Energy Change

The standard free-energy change, denoted as \( \Delta G^0 \), indicates the spontaneity of a reaction under standard conditions (1 atm pressure, 1 M concentration, and 298 K temperature). A positive \( \Delta G^0 \) means the reaction is non-spontaneous under these conditions and does not proceed as written without the input of external energy.

Understanding Free-Energy Change

The free-energy change, denoted as \( \Delta G \), tells us about the spontaneity of a reaction under given conditions. If \( \Delta G \) is positive, the reaction is non-spontaneous under those specific conditions, meaning it does not proceed as written without the input of energy.

Interpreting Exergonic Reactions

A reaction is considered exergonic if it releases energy, meaning \( \Delta G < 0 \). This implies that the reaction is spontaneous and can proceed as written under the given conditions, contributing to the work done by the system.

Key concepts

standard free-energy change

The standard free-energy change, also known as \( \Delta G^0 \), is an essential concept in understanding biochemical reactions. This term is specific to standard conditions, which include:

• 1 atm pressure
• 1 M concentration of all reactants and products
• A temperature of 298 K

When we talk about \( \Delta G^0 \), we're exploring whether a reaction will naturally proceed without the need for additional energy.
A positive \( \Delta G^0 \) means the reaction is non-spontaneous under these standard conditions. That tells us the reaction will not move forward on its own; instead, it requires an input of energy to proceed. Conversely, a negative \( \Delta G^0 \) signifies a spontaneous reaction, indicating that it can proceed without any external energy input. This distinction is crucial for predicting how biochemical processes behave in a controlled, standard environment.

spontaneity of reactions

In biochemical reactions, the spontaneity is determined by the free-energy change, denoted as \( \Delta G \). This value tells us whether a reaction can occur on its own under given conditions.
When \( \Delta G \) is negative, the reaction is spontaneous, meaning it can proceed without needing any additional energy. However, a positive \( \Delta G \) indicates that the reaction is non-spontaneous. This means energy must be supplied for the reaction to occur.
Understanding spontaneity is key in biochemistry because it helps us predict and control biochemical pathways. It's especially important in biological systems, where processes must be efficient and timely. To summarize:

• A negative \( \Delta G \)= spontaneous reaction
• A positive \( \Delta G \)= non-spontaneous reaction

This insight is essential for both theoretical predictions and practical applications in biochemistry.

exergonic reactions

Exergonic reactions are those that release energy during the process of the reaction. These reactions are characterized by a negative free-energy change, \( \Delta G < 0 \). This means that they are spontaneous and capable of doing work.
Exergonic reactions are vital in biochemistry because they drive many of the body's essential processes. For example:

• Cellular respiration, where glucose is broken down to release energy
• ATP hydrolysis, which provides energy for various cellular activities

This type of reaction is what powers life's many biochemical reactions, allowing organisms to grow, reproduce, and maintain their structure.
Understanding exergonic reactions helps us grasp how cells harness and utilize energy effectively. A key idea here is:
When a reaction is exergonic, \( \Delta G \) is less than zero, signaling that the reaction can occur spontaneously with energy release. This is the basis for numerous natural processes that keep life functional and thriving.