Conserved in a chemical reaction
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Conservation in Chemical Reactions: Key Insights and Principles
Conservation of Mass in Chemical Reactions
The principle of mass conservation is fundamental in chemical reactions. It states that the total mass of reactants equals the total mass of products in a closed system. This principle is crucial for understanding chemical processes and is often used to balance chemical equations. However, students often struggle with this concept, particularly in distinguishing between open and closed systems. Common misconceptions include the belief that mass increases in a precipitation reaction because the precipitate is solid and heavier than a liquid, or that mass decreases in a closed system during combustion2.
Conservation of Chemical Elements
While the masses of individual molecules may change during a chemical reaction, the masses of the nuclei of the chemical elements involved remain conserved. This is expressed through differential conservation equations, which show that the total mass, charge, and energy are conserved quantities with zero source terms. These conserved densities are linear combinations of the densities of reacting molecules, weighted by the number of atoms of each element in the species1.
Conservation Laws in Chemical Reaction Networks
In chemical reaction networks (CRNs), conservation laws play a significant role in determining the system's behavior. The conservation of mass, energy, and charge can be used to decompose entropy production and understand the dynamics of the system. For instance, in open CRNs, the potential change and work contributions due to nonconservative forces are crucial for describing the system's nonequilibrium thermodynamics5. Additionally, the conservation dependency graph is a useful tool for identifying conserved sets in reaction systems, which can help in understanding the relationships between different species4.
Nonlinear Kinetic Conservation Laws
Nonlinear kinetic conservation laws (NKCLs) provide a new approach to understanding chemical reactions, particularly those proceeding according to linear multistage mechanisms in isothermal gradientless reactors. These laws are derived from data measured in single non-stationary experiments and offer insights into the specific reactions occurring in closed and open systems7.
Mass Conservation and Reaction Mechanisms
The stoichiometric matrix of a reaction mechanism is essential for determining mass-conservation equations. A proposed mechanism must be tested to ensure it is conservative, meaning it adheres to the closed-system assumption. Tools like the JSTOICH applet can be used to determine the number and set of mass-conservation equations implied by the stoichiometric matrix, providing a systematic way to analyze reaction mechanisms9.
Energy Conservation in Chemical Reactions
The law of conservation of energy is another critical principle in chemical reactions. It has been shown that the form of this law can explain discrepancies observed in chemical thermodynamics, such as differences in the heat of chemical processes measured by calorimetry and the Van't Hoff equation. This understanding is crucial for accurately describing the energy changes that occur during chemical reactions6.
Conclusion
The conservation principles in chemical reactions, including mass, energy, and chemical elements, are fundamental to understanding and predicting the behavior of chemical systems. These principles are expressed through various conservation laws and equations, which provide a framework for analyzing chemical reactions in both closed and open systems. Understanding these concepts is essential for students and researchers alike, as they form the basis for much of modern chemistry and chemical engineering.
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Conservation Equations for Chemical Elements in Fluids with Chemical Reactions
In fluids with chemical reactions, conserved densities can be found for each chemical element, based on linear combinations of reacting molecules containing the element, without needing to know the reactions involved.
STUDENTS DIFFICULTIES IN UNDERSTANDING OF THE CONSERVATION OF MATTER IN OPEN AND CLOSED-SYSTEM CHEMICAL REACTIONS
Students have misconceptions about conservation of matter in chemical reactions, such as the total mass increasing in precipitation reactions and the total mass decreasing in closed systems.
Highly CitedA Continuum theory of chemically reacting media—I
This paper presents a unified approach for analyzing conservation of mass, balance of momenta, conservation of energy, balance of entropy, and simultaneous reactions in chemically reacting continuums.
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