physical chemistry

Quick and Easy Explanation of Physical Chemistry

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We hope you’ve enjoyed looking at the branches of chemistry so far. Next up is physical chemistry! There’s a little more to it, but like the name suggests, you can think of it as a blend of physics and chemistry. So what does that actually mean? Here are some physical chemistry examples and a look at the broader goals of the discipline itself.

What Is Physical Chemistry?

Physical chemistry studies the physical properties of chemical substances — all matter — as well as chemical reactions at the atomic and molecular levels.

We have matches and Zippo lighters today because we have observed and can now reproduce the chemical processes that reliably yield fire. We like to say that we have “mastered fire” — and the science of physical chemistry (and some burned fingers) got us there.

Chemical changes (chemical reactions) are different from physical changes or physical reactions. Physical chemistry is concerned with the former, but it has implications in the latter — that is, in how “things behave” in the real world we see and touch every day.

Chemical reactions include things like burning wood, the oxidation of metals and the digestive processes. In all of these, chemical bonds are broken and new ones are formed.

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What Will Scientists Discover Next?


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Observing physical changes helps us understand and exploit, for example, why and when matter changes states and the point at which metals and alloys break instead of bend. With physical changes, it’s the same “stuff.” It hasn’t changed chemically. But through physical chemistry and other branches of science, we can make “better stuff.” And that’s just part of it.

Practicing physical chemistry uses the following vantage points to make observations as we learn how to exploit chemical changes and material properties:

  • Macroscopic: How do larger amounts of matter behave under different circumstances? What are their melting and boiling points? How well do they conduct heat? Which materials can withstand the desired levels of stress-testing?
  • Microscopic: Light microscopes, scanning probe microscopes and electron microscopes help us observe what materials “do” beyond our ability to observe them directly. How do crystals form the way they do? Why does this solvent work the way it does?
  • Atomic: From this vantage point, physical chemistry observes the properties of the elements themselves and how and when they form compounds.
  • Subatomic and nuclear: Physical chemistry at the subatomic and nuclear level is concerned with how protons, neutrons and electrons function and how energy itself behaves.

Why Is Physical Chemistry Useful?

Making observations at these scales helps us better understand how the physical world “works,” how simple and complex structures function and form, and how humankind can exploit chemical reactions to make new reactions and materials of our own.

A physical chemist may begin with a prediction for how a chemical or a combination of materials might behave under certain conditions. They would then use sophisticated equipment to observe the desired reaction or phenomenon in a laboratory or a simulation to test that hypothesis and refine their goals and expectations for further tests.

These observations yield the many data points required by physical chemists to explain what they’re seeing in mathematical terms and to predict the same behavior later on in a different set of circumstances. Data helps place these new findings in context alongside the other observed properties of physical matter and makes them useful to members of other scientific fields and professional disciplines.

Think of the many times in history when a game-changing invention or discovery relied on the development of a new or improved material. For example: “If Widget X is made from Material B, it will yield a 5% improvement in tensile strength” or “With this type of fuel, we can escape earth’s gravity and atmosphere 10% more efficiently.”

Those are the types of hypotheses that got humanity to the moon and that will help us build better batteries, explore the hidden reaches of earth’s oceans and maybe even tackle that long-foretold space elevator. Physical chemistry doesn’t do it alone, but it plays a huge role.

What Are Some Physical Chemistry Examples?

You’re probably wondering how such a broad field keeps itself organized. Thankfully, physical chemistry can be broken down into several specific fields based on the portion of the physical world they’re exploring. These fields include:

  • Thermochemistry: Why do some chemical reactions give off heat while others do not? How can we repeat and control this reaction?
  • Electrochemistry: What do these protons and electrons do when an electrical current is applied?
  • Photochemistry: What is the effect of light on a particular chemical reaction?
  • Spectroscopy: What is the effect of radiation on reactions and why does some matter give off radiation?
  • Kinetics: Why do some chemical reactions proceed at one speed, and others at another?

Still too theoretical? Here are some specific examples of physical chemistry disciplines as well as related specialties that work closely with physical chemists or rely on the principles discovered through physical chemistry:

  • Material scientists
  • Molecular modelers and analytical chemists
  • Organic and inorganic chemists
  • Pharmacists
  • Cosmetic chemists
  • Heating and cooling engineers
  • Toxicologists
  • Forensic chemists
  • Hazardous waste chemists
  • Particle scientists
  • Biochemists and biotechnologists

A Truly Interdisciplinary Branch of Science

Physical chemists must be at home in a laboratory setting and able to use a variety of sophisticated instruments skillfully, including mass spectrometers, lasers, electron microscopes and nuclear magnetic resonance equipment.

Physical chemists must also be observant, detail-oriented and highly skilled in mathematics and data science. It’s not unusual for physical chemists to begin their careers with research lab fellowships for a year or more before finding a more stable, salaried position.

The most exciting takeaway about physical chemistry is how interdisciplinary it is. Discoveries made here resonate through metals and textiles, household products, pharmaceuticals and even quantum mechanics, making this one of the branches of chemistry most worthy of our respect and attention.

Quick and Easy Explanation of Physical Chemistry
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Article by: Megan Ray Nichols

Megan Ray Nichols is a freelance science writer and science enthusiast. Her favorite subjects include astronomy and the environment. Megan is also a regular contributor to The Naked Scientists, Thomas Insights, and Real Clear Science. When she isn't writing, Megan loves watching movies, hiking, and stargazing.