Reversible hydrogen electrode

Key takeaways

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

Reference excerpt

A reversible hydrogen electrode (RHE) is a reference electrode, more specifically a subtype of the standard hydrogen electrodes, for electrochemical processes. Unlike the standard hydrogen electrode, its measured potential does change with the pH, so it can be directly used in the electrolyte. The name refers to the fact that the electrode is directly immersed in the actual electrolyte solution and not separated by a salt bridge. The hydrogen ion concentration is therefore not 1 mol/L, or 1 mol/kg, but corresponds to that of the electrolyte solution. In this way, it is possible to achieve a stable potential with a changing pH value. The potential of the RHE correlates to the pH value:

E = 0.000 − 0.059 × p H {\displaystyle E=0.000-0.059\times \mathrm {pH} }

In general, for a hydrogen electrode in which the reduction of the hydronium ions (H3O+) occurs:

2 H 3 O + + 2 e − ↽ − − ⇀ H 2 + 2 H 2 O {\displaystyle {\ce {{2H3O+}+{2e^{-}}<=>{H2}+{2H2O}}}}

or, more often commonly written simply with H+ denoting H3O+:

2 H + + 2 e − ↽ − − ⇀ H 2 {\displaystyle {\ce {{2H+}+{2e^{-}}<=>{H2}}}}

with,

K = p H 2 ( aH + ) 2 {\displaystyle K={\frac {p{{\ce {H2}}}}{{\ce {(aH+)^2}}}}}

the equilibrium potential E depends on the hydrogen pressure pH2 and the activity aH+ as follows:

E = E ⊖ − R T z F ln ⁡ K {\displaystyle E=E^{\ominus }-{\frac {RT}{zF}}\ln K}

E = E ⊖ − R T 2 F ln ⁡ p H 2 ( aH + ) 2 {\displaystyle E=E^{\ominus }-{\frac {RT}{2F}}\ln {\frac {p{{\ce {H2}}}}{{\ce {(aH+)^2}}}}}

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Reversible hydrogen electrode

Start with the simplest possible case. Write down what Reversible hydrogen electrode claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Reversible hydrogen electrode 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 Reversible hydrogen electrode 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 Reversible hydrogen electrode

In research: Reversible hydrogen electrode appears in science 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 Reversible hydrogen electrode 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: Reversible hydrogen electrode is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrodes, Hydrogen technologies, so understanding it makes those chapters shorter.
In everyday life: Look for Reversible hydrogen electrode 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.

How to study Reversible hydrogen electrode in 20 minutes

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

Frequently asked questions

What is Reversible hydrogen electrode in simple terms?

A reversible hydrogen electrode (RHE) is a reference electrode, more specifically a subtype of the standard hydrogen electrodes, for electrochemical processes. Unlike the standard hydrogen electrode, its measured potential does change with the pH, so it can be directly used in the electrolyte.

Why does Reversible hydrogen electrode matter?

Because it connects several science 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 Reversible hydrogen electrode?

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 Reversible hydrogen electrode.