6.8 Describing a Reaction: Bond Dissociation Energies
2 min read•may 7, 2024
Bond dissociation energies are key to understanding reaction energetics. They tell us how much energy it takes to break specific bonds, helping predict if reactions will release or absorb energy overall.
in our bodies, like ATP, have weak bonds that break easily to power cellular processes. This connects to how the strength of chemical bonds influences energy storage and release in living systems.
Bond Dissociation Energies and Reaction Energetics
Calculation of bond dissociation energy
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- () quantifies energy required to break a specific bond in a molecule
- Expressed in units of or
- Each bond type has a characteristic BDE value
- BDE approximately 413 kJ/mol
- Calculate energy required to break a bond using the specific bond's BDE value
- Breaking a C-H bond requires 413 kJ/mol of energy input
- When breaking multiple bonds, sum the BDE values for each bond to determine total energy required
- Breaking two C-H bonds requires 2 × 413 kJ/mol = 826 kJ/mol of energy
Bond strengths and reaction thermodynamics
- release energy as they proceed
- Product bonds are stronger than reactant bonds
- Difference in bond strengths results in net energy release
- absorb energy as they proceed
- Reactant bonds are stronger than product bonds
- Difference in bond strengths results in net energy absorption
- Overall reaction energy change depends on balance between energy required to break bonds and energy released when new bonds form
- If more energy is released than absorbed, reaction is exothermic (negative )
- If more energy is absorbed than released, reaction is endothermic (positive )
- influences the change of a reaction
High-energy compounds in biochemistry
- High-energy compounds have relatively weak bonds easily broken to release energy
- and
- Energy released from breaking weak bonds drives other cellular processes
- () releases energy for biochemical reactions
- Compounds with stronger bonds are more stable and less likely to release energy under physiological conditions
- Amino acids and proteins have strong , making them stable and less reactive
- Relative bond strengths of biomolecules determine reactivity and energy storage capacity in living systems
- (glucose) have weaker bonds than proteins, allowing for easier energy release
- (fatty acids) have strong C-C and C-H bonds, serving as efficient energy storage molecules
Thermochemistry and Reaction Kinetics
- studies heat changes in chemical reactions
- Bond dissociation energies are crucial in determining reaction enthalpy
- represents the minimum energy required for a reaction to occur
- Bond strength influences the activation energy needed to initiate a reaction
Key Terms to Review (23)
$ ext{Δ H}$: $ ext{Δ H}$ is a thermodynamic quantity that represents the change in enthalpy, or the total heat energy, of a system during a chemical reaction or physical process. It is a crucial factor in understanding and describing the energetics of a reaction.
Activation Energy: Activation energy is the minimum amount of energy required to initiate a chemical reaction. It represents the energy barrier that reactants must overcome in order to form products. This concept is central to understanding the mechanisms and kinetics of organic reactions.
Activation energy, ΔG‡: Activation energy (ΔG‡) is the minimum amount of energy required to initiate a chemical reaction, specifically the energy needed to reach the transition state from the reactants. It's a crucial factor in determining the rate at which a reaction will occur in organic chemistry.
ATP (Adenosine Triphosphate): ATP, or adenosine triphosphate, is the primary energy currency of living cells. It is a high-energy nucleotide that stores and transfers the energy needed to power various cellular processes, from muscle contraction to protein synthesis. ATP is central to the understanding of bond dissociation energies, biological substitution reactions, metabolism, and energy production in the body.
ATP Hydrolysis: ATP hydrolysis refers to the chemical reaction in which the high-energy phosphate bond in adenosine triphosphate (ATP) is broken, releasing energy that can be used to drive various cellular processes. This reaction is a fundamental aspect of energy metabolism and is closely connected to the topics of bond dissociation energies and the overview of metabolism and biochemical energy.
BDE: BDE, or Bond Dissociation Energy, refers to the amount of energy required to break a specific chemical bond within a molecule. It is a fundamental concept in understanding the stability and reactivity of chemical species.
Bond Dissociation Energy: Bond dissociation energy is the amount of energy required to break a specific chemical bond between two atoms, separating them into individual, free atoms. This term is crucial in understanding the stability and reactivity of molecules, as well as the energetics of chemical reactions.
Bond dissociation energy (D): Bond dissociation energy is the amount of energy required to break a particular bond in a molecule in the gas phase, leading to the formation of separate, neutral atoms. It is a measure of the bond strength and stability in a chemical compound.
Bond dissociation energy, D: Bond dissociation energy is the amount of energy required to break a bond between two atoms in a molecule into two separate, radical species. It is measured in kilojoules per mole (kJ/mol) and varies depending on the type of bond and the molecules involved.
Bond Strength: Bond strength refers to the force that holds atoms together in a chemical bond. It is a measure of the energy required to break or dissociate a chemical bond, and it is an important factor in determining the stability and reactivity of molecules.
C-H Bond: The C-H bond is a covalent bond formed between a carbon atom and a hydrogen atom. This bond is fundamental to organic chemistry and is present in a wide range of organic compounds, from simple alkanes to complex biomolecules. The C-H bond is crucial in understanding the structure, reactivity, and stability of organic molecules.
Carbohydrates: Carbohydrates are a class of macromolecules composed of carbon, hydrogen, and oxygen atoms. They serve as a primary source of energy for the body and play crucial roles in cellular structure and function, particularly in the context of bond dissociation energies.
Endothermic Reactions: Endothermic reactions are chemical processes that absorb energy from the surroundings in the form of heat. This energy is required to break the bonds within the reactant molecules, enabling the formation of new products.
Enthalpy: Enthalpy is a measure of the total energy of a thermodynamic system, including both the internal energy and the work done by or on the system due to changes in pressure and volume. It is a crucial concept in understanding the energy changes that occur during chemical reactions and phase transitions.
Enthalpy change (ΔH): Enthalpy change is the heat absorbed or released by a system during a chemical reaction at constant pressure. It is a key factor in determining whether a reaction is endothermic (absorbing heat) or exothermic (releasing heat).
Exothermic Reactions: An exothermic reaction is a chemical reaction that releases energy in the form of heat to the surrounding environment. This release of heat energy is a key feature of exothermic reactions, which is particularly relevant in the context of understanding bond dissociation energies.
Glucose: Glucose is a simple sugar, or monosaccharide, that serves as the primary source of energy for the body's cells. It is a key component in various metabolic processes and plays a central role in carbohydrate chemistry and biochemistry.
High-Energy Compounds: High-energy compounds are molecules that store a significant amount of potential energy in their chemical bonds, which can be released through exergonic (energy-releasing) reactions. These compounds play a crucial role in various biological processes, particularly in the context of energy transfer and storage within living organisms.
Kcal/mol: Kilocalories per mole (kcal/mol) is a unit of measurement that represents the amount of energy required to break or form a chemical bond. It is commonly used in the context of bond dissociation energies, which describe the energy needed to separate a molecule into its constituent atoms or fragments.
KJ/mol: kJ/mol, or kilojoules per mole, is a unit of measurement used to quantify the energy changes associated with chemical reactions. It represents the amount of energy, in kilojoules, required to either break apart or form one mole of a particular chemical bond or compound.
Lipids: Lipids are a diverse group of naturally occurring organic compounds that are insoluble in water but soluble in organic solvents. They play crucial roles in the structure and function of cells, as well as in various biological processes, including energy storage and signaling.
Peptide Bonds: A peptide bond is a covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another amino acid, resulting in the creation of a polypeptide chain. These bonds are central to the structure and function of proteins, which are essential macromolecules in biological systems.
Thermochemistry: Thermochemistry is the study of the energy changes that occur during chemical reactions and physical transformations. It examines the relationship between chemical processes and the transfer of heat, providing a fundamental understanding of the energetic aspects of chemical systems.