Question

Reactions that release free energy are a. exergonic. b. spontaneous. c. endergonic. d. endothermic. e. both a and b.

Short answer

The correct answer is e. both a and b, i.e., Exergonic and Spontaneous.

Step-by-step solution

Understand the terms.

In thermodynamics, the terms are defined as follows: \n- Exergonic reactions: These are reactions that release energy, typically in the form of heat or light, making the products of the reaction more stable than the reactants. \n- Spontaneous reactions: These are reactions that occur naturally, without any added external energy. \n- Endergonic reactions: These reactions absorb energy during the process of the reaction. \n- Endothermic reactions: These are reactions that take up heat energy from the surroundings, and are a subset of endergonic reactions.

Match the definitions with the answers.

As per the definitions provided, the reactions which release free energy can be categorized as exergonic and spontaneous.

Key concepts

Spontaneous Reactions

Spontaneous reactions are fascinating phenomena in chemistry where reactions occur naturally and without any additional input of energy. These reactions have a mind of their own and can proceed on their own accord when the conditions are right.
The driving force behind spontaneous reactions is the inherent energy balance within the system. The products of these reactions are more thermodynamically stable compared to the reactants, which means there is less free energy in the products. This energy difference allows the reaction to move forward without requiring external energy sources.
Some key points to know about spontaneous reactions include:

• They generally lead to an increase in disorder or entropy in the system, aligning with the second law of thermodynamics.
• Spontaneity does not imply speed; it only indicates that a reaction is capable of occurring under given conditions.
• Temperature and pressure can influence the spontaneity of reactions.

Thermodynamics

Thermodynamics is a branch of physics that enables us to understand how energy transformations occur in chemical reactions. It provides the rules governing energy changes, including heat and work, during any type of physical and chemical process.
In the context of chemistry, thermodynamics helps predict whether a reaction can spontaneously occur by examining energy and entropy aspects.
In order to assess reaction spontaneity, two fundamental quantities are typically considered:

• Enthalpy (H): Represents the heat content of a system. Changes in enthalpy can indicate whether the reaction absorbs or releases energy.
• Entropy (S): Measures the randomness or disorder within a system. A greater increase in entropy suggests a more spontaneous process.
• Gibbs Free Energy (G): Defined as the energy available to do work in a system, calculated using the equation \[G = H - TS\] where \(T\) is the temperature in Kelvin. Negative changes in Gibbs free energy (\(\Delta G\)) typically signal spontaneous reactions.

Energy Release

Energy release is a core aspect of many chemical reactions, particularly exergonic reactions. During these reactions, energy that was stored in chemical bonds is liberated, typically in the form of heat or light.
This release of energy happens because the products of the reaction possess lower energy than the reactants themselves, making the whole system more stable. The release of energy is a driving force for these reactions to occur spontaneously.
Important points about energy release include:

• It contributes to making a reaction spontaneous and often leads to the generation of heat, making the surroundings warmer.
• Energy release is not just limited to heat; it can also be in the form of light or sound.
• Reactions that release energy are reflected by a negative sign in the change of enthalpy (\(\Delta H\)), indicating an exothermic process.

Chemical Reactions

Chemical reactions are the processes that transform substances into different compounds and rely extensively on both energy input and release. In a typical chemical reaction, bonds in reactants break and new bonds form in products, leading to either the release or absorption of energy.
The overall balance of these energies determines whether a reaction is exergonic (releases energy) or endergonic (absorbs energy). Understanding chemical reactions involves looking at many factors, including reaction conditions, reactant states, and thermodynamic properties.
Key considerations for chemical reactions include:

• Reaction rate: Influenced by factors like temperature, concentration, and presence of catalysts.
• Equilibrium: A state where the forward and reverse reactions occur at equal rates, leading to a stable composition of reactants and products.
• Energy diagrams: Visual tools showing energy changes during a reaction, highlighting activation energy and the difference between reactants and products' energy levels.