physics

Kopp's law

Kopp's law is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Kopp's law rather than just read about it. In short: Kopp's law can refer to either of two relationships discovered by the German chemist Hermann Franz Moritz Kopp (1817–1892). Kopp found "that the molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it; the elements having atomic heat capacities lower than those required by the Dulong–Petit law retain these lower values in their compounds".

Key takeaways

Kopp's law belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Kopp's law to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Kopp's law from memory before moving on to harder problems.

Reference excerpt

Kopp's law can refer to either of two relationships discovered by the German chemist Hermann Franz Moritz Kopp (1817–1892).

Kopp found "that the molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it; the elements having atomic heat capacities lower than those required by the Dulong–Petit law retain these lower values in their compounds". In studying organic compounds, Kopp found a regular relationship between boiling points and the number of CH2 groups present.

Kopp–Neumann law The Kopp–Neumann law, named for Kopp and Franz Ernst Neumann, is a common approach for determining the specific heat C (in J·kg−1·K−1) of compounds using the following equation:

C = ∑ i = 1 N C i f i , {\displaystyle C=\sum _{i=1}^{N}C_{i}f_{i},} where N is the total number of compound constituents, and Ci and fi denote the specific heat and mass fraction of the i-th constituent. This law works surprisingly well at room-temperature conditions, but poorly at elevated temperatures.

Illustrations

Worked examples

Example 1 — a first encounter with Kopp's law

Start with the simplest possible case. Write down what Kopp's law claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Kopp's law before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Kopp's law ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Kopp's law

In research: Kopp's law appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Kopp's law in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Kopp's law is common in secondary-school and first-year university syllabi. It links to neighbouring topics Laws of thermodynamics, Thermodynamics stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Kopp's law outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Kopp's law in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kopp's law means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Kopp's law out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kopp's law in simple terms?

Kopp's law can refer to either of two relationships discovered by the German chemist Hermann Franz Moritz Kopp (1817–1892). Kopp found "that the molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it; the elements having atomic heat capacit…

Why does Kopp's law matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Kopp's law?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Kopp's law.