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Learn Physical Chemistry

Use physics and math to explain why reactions happen and how fast.

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Physical chemistry explains chemical behavior with the tools of physics and mathematics. It answers three big questions: will a reaction happen, where will it settle, and how fast will it get there. Those answers come from thermodynamics, equilibrium and kinetics, while quantum chemistry explains bonding and spectra from the Schrodinger equation. It is often considered the most mathematical chemistry course, built on calculus. A good starting point is energy, enthalpy and entropy before moving to rate laws and quantum models. Learnr shapes a physical chemistry course to your needs and teaches it through short interactive lessons.

How to learn Physical Chemistry, step by step

Refresh calculus before you start. Physical chemistry uses derivatives, integrals and partial derivatives constantly, along with logarithms and exponentials. Review integrating 1/x and exponential functions, since they appear in gas expansion and kinetics problems alike.
Build thermodynamics from state functions. Learn why enthalpy, entropy and Gibbs energy depend only on state, not path, then use Hess's law and standard formation values. Practice predicting spontaneity from the signs of delta H and delta S at different temperatures.
Link free energy to equilibrium. Use delta G = -RT ln K to move between thermodynamic data and equilibrium constants, and the van't Hoff equation for temperature changes. Read phase diagrams for water and carbon dioxide and locate the triple point.
Fit kinetics data to rate laws. Use integrated rate laws for zero, first and second order reactions, and find the order by which plot gives a straight line. Then fit an Arrhenius plot of ln k against 1/T to get activation energy.
Learn quantum chemistry with model systems. Solve the particle in a box, then meet the harmonic oscillator, rigid rotor and hydrogen atom. Each model explains a type of spectroscopy, such as vibrational or rotational, so learn them together.
Do derivations by hand, a little at a time. Rewriting a derivation from memory teaches more than rereading it. Combine that with brief daily Learnr problem sets so formulas and units do not slip between units of the course.

What you'll learn

Use enthalpy, entropy and Gibbs free energy to predict whether a reaction is spontaneous
Relate standard Gibbs energy to the equilibrium constant with delta G = -RT ln K
Determine rate laws and reaction orders from experimental data
Use the Arrhenius equation to find activation energy from rate constants
Solve the particle in a box and connect quantized energy levels to spectroscopy

What's inside your Physical Chemistry course

A sample path Learnr builds for Physical Chemistry. Your real course adapts to your goal and level.

1. Gases and the laws of thermodynamics
2. Enthalpy, entropy and Gibbs free energy
3. Chemical equilibrium and phase diagrams
4. Electrochemistry and the Nernst equation
5. Chemical kinetics and reaction mechanisms
6. Quantum chemistry and spectroscopy

How long does it take to learn Physical Chemistry?

Physical chemistry is usually taught over two undergraduate semesters, about 6 to 9 months at 6 to 8 hours a week, one on thermodynamics and kinetics and one on quantum chemistry. Strong calculus shortens the ramp, while weak math stretches it noticeably.

What you need before you start

General chemistry, single-variable calculus and ideally some multivariable calculus and introductory physics. Differential equations and linear algebra help for the quantum half.

Common mistakes to avoid

Confusing delta G with standard delta G. The standard value fixes the equilibrium constant, while the actual delta G depends on current concentrations.
Thinking a spontaneous reaction must be fast. Thermodynamics says whether a reaction can happen, while kinetics says how quickly, and diamond turning to graphite shows the difference.
Mixing units of the gas constant. Use 8.314 J per mol per kelvin with energies in joules, and convert kilojoules before plugging in.

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Physical Chemistry questions, answered

Why is physical chemistry considered so hard?

It combines chemistry with calculus-based physics and expects you to follow derivations, not just apply formulas. With solid math preparation and steady practice, it becomes much more manageable.

What is the difference between thermodynamics and physical chemistry?

Thermodynamics is one part of physical chemistry. Physical chemistry also includes kinetics, quantum chemistry, spectroscopy and statistical mechanics applied to chemical systems.

Do I need physical chemistry for medicine or biology?

Many pre-health programs require only general and organic chemistry, but biochemistry and pharmacology use physical chemistry ideas like binding equilibria and reaction rates. Check the requirements of your specific program.