chemistry

Latimer diagram

Latimer diagram is a chemistry 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 Latimer diagram rather than just read about it. In short: A Latimer diagram of a chemical element is a summary of the standard electrode potential data of that element. This type of diagram is named after Wendell Mitchell Latimer (1893–1955), an American chemist.

Key takeaways

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

Reference excerpt

A Latimer diagram of a chemical element is a summary of the standard electrode potential data of that element. This type of diagram is named after Wendell Mitchell Latimer (1893–1955), an American chemist.

Construction In a Latimer diagram, because by convention redox reactions are shown in the direction of reduction (gain of electrons), the most highly oxidized form of the element is on the left side, with successively lower oxidation states to the right side. The species are connected by arrows, and the numerical value of the standard potential (in volts) for the reduction is written at each arrow. For example, for oxygen, the species would be in the order O2 (0), H2O2 (–1), H2O (-2):

The arrow between O2 and H2O2 has a value +0.68 V over it, it indicates that the standard electrode potential for the reaction:

O2(g) + 2 H+ + 2 e− ⇌ H2O2(aq) is 0.68 volts.

Application Latimer diagrams can be used in the construction of Frost diagrams, as a concise summary of the standard electrode potentials relative to the element. Since ΔrGo = -nFEo, the electrode potential is a representation of the Gibbs energy change for the given reduction. The sum of the Gibbs energy changes for subsequent reductions (e.g. from O2 to H2O2, then from H2O2 to H2O) is the same as the Gibbs energy change for the overall reduction (i.e. from O2 to H2O), in accordance with Hess's law. This can be used to find the electrode potential for non-adjacent species, which gives all the information necessary for the Frost diagram. It must be stressed that standard reduction potentials are not additive values. They cannot be directly summed up, or subtracted, from the values (in volts) indicated in a Latimer diagram. If needed, their calculation must be performed via the difference in Gibbs free energies. The easiest way to proceed is simply to use energies (nE) directly expressed in electron-volts (eV), because the Faraday constant F and the sign minus simplifies on both side of the equation. So, the values of Eo in volts must be simply multiplied by the number (n) of electrons transferred in the half-reaction. Since the Faraday constant can disappear from the equation, no need to calculate ΔrGo expressed in joules. A Latimer diagram can also indicate if a species will disproportionate in solution under the conditions for which the electrode potentials are given: if the same number of electrons are exchanged in each reaction, and if the potential to the right of the species is higher than the potential on the left, it will disproportionate. Therefore, hydrogen peroxide H2O2 is unstable and will disproportionate into O2 and H2O.

See also Frost diagram Pourbaix diagram Ellingham diagram

References

Illustrations

Worked examples

Example 1 — a first encounter with Latimer diagram

Start with the simplest possible case. Write down what Latimer diagram claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Latimer diagram 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 Latimer diagram 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 Latimer diagram

In research: Latimer diagram appears in chemistry 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 Latimer diagram 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: Latimer diagram is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrochemistry, Potentials, so understanding it makes those chapters shorter.
In everyday life: Look for Latimer diagram 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 Latimer diagram in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Latimer diagram 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 Latimer diagram out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Latimer diagram in simple terms?

Why does Latimer diagram matter?

Because it connects several chemistry 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 Latimer diagram?

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 Latimer diagram.