By Angela Anderson, M.Ed.
Physics and chemistry are highly interconnected fields, and their relationship is based on fundamental understandings in the behavior of matter and energy. Many physics principles, such as Newton’s laws of motion and the laws of thermodynamics, are crucial for studying chemical reactions and changes in state, (Jagodzinski, 2008). Outside of Newtonian physics, principles of quantum mechanics such as wave-particle duality and the Schrödinger equation are foundational for understanding chemical bonding and spectroscopy, (Mombourquette, 2022). Digging into each of these sub-topics further, we can better understand the value in the interconnectedness of these sciences.
Newtonian Physics
Newton’s laws of motion center on three statements that describe the relationships between forces acting on a body and the motion of the body, first formulated by English physicist and mathematician Isaac Newton, (Encyclopædia Britannica, n.d.). Newton's first law states that an object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by a net external force. In chemistry, this law is relevant when considering reactions and molecular motion. For example, understanding the inertia of particles helps explain why reaction rates can change based on factors like temperature and concentration, (Jagodzinski, 2008).
The second law describes the relationship between the force applied to an object, its mass, and its acceleration (F=ma). In the context of chemistry, this law helps us understand the forces involved in chemical reactions. During a collision, the force exerted between molecules can affect reaction rates, and the acceleration of particles is related to the energy changes in a reaction, (Khan Academy, n.d.).
Newton's third law states that for every action, there is an equal and opposite reaction. In chemistry, this law is evident in the principle of conservation of momentum. Relating back to reaction rates, we can find that chemical reactions which involve a collision of molecules provides that the force exerted by one molecule on another is equal and opposite, leading to exchanges in the momentum of the reacting particles, (Khan Academy, n.d.).
Thermodynamics
It is also evident that the laws of thermodynamics are equally applicable to both physics and chemistry, providing a unified framework for understanding energy transformations. Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of a French physicist named Sadi Carnot who believed that engine efficiency was the key that could help France win the Napoleonic Wars throughout the early 1800s, (Clausius, 2003). Today, we see that this subclass of physics is now used across numerous scientific fields; including chemistry, geology, and biological engineering, (Garcia, et al., 2011; White, 2013). Chemical thermodynamics pertains to the interrelation of heat with chemical reactions or with physical changes of state based on the initial laws of thermodynamics, (Callen, 1960).
The first law of thermodynamics asserts that the total energy of the system (reactants + products) is conserved. The energy released during the reaction can be in the form of heat (Q) or used to perform work (W), demonstrating the law of energy conservation, (University of North Carolina, n.d.).
The second law predicts that spontaneous processes tend to increase the overall entropy of a system. In isolated chemical systems, all spontaneous changes occur with an increase in entropy, signifying that the total entropy change for the system is always positive, (University of North Carolina, n.d.).
The third law of thermodynamics suggests that as the temperature approaches absolute zero (0 K), the entropy of the system approaches a minimum value. Molecules near these temperatures have been called “the fifth state of matter,” also known as Bose–Einstein condensates, and give way to studies such as cryogenics (the study of materials at very low temperatures) and superconductivity (conducting electric current without resistance), (Science Direct, n.d.).
Quantum Mechanics
Lastly, the fields of physics and chemistry intersect through the study of quantum mechanics. According to wave-particle duality, particles exhibit both wave-like and particle-like properties. Electrons and atomic orbitals, exhibit wave-like behavior and are described using functions of wave-particle duality, (Mombourquette, 2022). The Schrödinger equation, developed by Austrian physicist Erwin Schrödinger in 1925, works to describe the energy and position of an electron in space and time by considering it’s matter wave nature, (Griffiths, 2004).
Understanding this duality is integral to the understanding of atomic structures and the basis for molecular bonding. Furthermore, quantum mechanics is essential to the understanding of energy transitions that occur in spectroscopy. The quantization of energy levels, as predicted by the Schrödinger equation, gives way for interpreting spectral lines, (Mombourquette, 2022).
References
Encyclopædia Britannica. (n.d.). Newton’s second law: F = ma. Encyclopædia Britannica. Retrieved November 22, 2023, from https://www.britannica.com/science/Newtons-laws-of-motion/Newtons-second-law-F-ma
Callen, H. B. (1960). Thermodynamics: An introduction to the physical theories of equilibrium thermostatics . John Wiley and Sons.
Clausius, R. (2003). On a mechanical theorem applicable to heat. History of Modern Physical Sciences, 172–178. https://doi.org/10.1142/9781848161337_0012
Garcia, H. G., Kondev, J., Orme, N., Theriot, J. A., & Phillips, R. (2011). Thermodynamics of Biological Processes. Methods in enzymology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3264492/#:~:text=Thermodynamics%20has%20long%20been%20a,state%20of%20the%20cellular%20interior.
Griffiths, David J. (2004). Introduction to Quantum Mechanics (2nd ed.). Prentice Hall. ISBN 978-0-13-111892-8.
Khan Academy. (n.d.). Factors affecting reaction rates (video). Khan Academy. https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:kinetics/x2eef969c74e0d802:reaction-rates/v/factors-affecting-reaction-rates
Mombourquette, M. (2022). Quantum Mechanics. E-Campus Ontario. https://ecampusontario.pressbooks.pub/queenschem1/chapter/chapter-6-quantum-mechanics/
Jagodzinski, F. (2008). Newton’s laws of Motion. https://facultyweb.cs.wwu.edu/~jagodzf/pdfs/MDEquations.pdf
Science Direct. (n.d.). Third law of thermodynamics. Third Law of Thermodynamics - an overview | ScienceDirect Topics. https://www.sciencedirect.com/topics/chemistry/third-law-of-thermodynamics#:~:text=The%20third%20law%20of%20thermodynamics%20states%20that%20the%20entropy%20of,different%20ground%20states%20it%20has.
Science History Institute. (2023). Amedeo Avogadro. Science History Institute. https://www.sciencehistory.org/education/scientific-biographies/amedeo-avogadro/#:~:text=Avogadro’s%20Hypothesis&text=Avogadro%20also%20astutely%20reasoned%20that,molecule%20were%20used%20almost%20interchangeably.
University of North Carolina. (n.d.). Thermodynamics. Chemical thermodynamics. http://www.shodor.org/UNChem/advanced/thermo/index.html
White, W. M. (2013). In Geochemistry (p. 114–155). Wiley
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