The electric potential at the interface

The potential at the interface can be analysed by imagining the separation of the electrode from the solution, but with the charges of the metal and the solution frozen in position. A positive test charge at great distances from the isolated electrode experiences a Coulomb potential that varies inversely with distance (Fig. 25.33). As the test charge approaches the electrode, which can be a metal or membrane electrode, it enters a region where the potential varies more slowly. This change in behaviour can be traced to the fact that the surface charge is not point-like but is spread over an area. At about 100 nm from the surface the potential varies only slightly with distance because the closer the point of observation is to the surface, although the potential from a given region of charge is stronger, a smaller area of surface is sampled (Fig. 25.34). The potential in this region is called the outer potential, ψ. As the test charge is taken through the skin of electrons on the surface of the electrode, the potential it experiences changes until the probe reaches the inner, bulk metal environment, where the potential is called the inner potential, φ. The difference between the inner and outer potentials is called the surface potential, χ. A similar sequence of changes of potential is observed as a positive test charge is brought up to and through the solution surface. The potential changes to its outer value as the charge approaches the charged medium, then to its inner value as the probe is taken into the bulk. Now consider bringing the electrode and solution back together again but without any change of charge distribution. The potential difference between points in the bulk metal and the bulk solution is the Galvani potential difference, ∆φ. Apart from a constant, this Galvani potential difference is the electrode potential that was discussed in Chapter 7. We shall ignore the constant, which cannot be measured anyway, and identify changes in ∆φ with changes in electrode potential (see Further information 25.1 for a quantitative treatment).

Fig. 25.33 The variation of potential with distance from an electrode that has been separated from the electrolyte solution without there being an adjustment of charge. A similar diagram applies to the separated solution.

Fig. 25.34 The origin of the distance independence of the outer potential. (a) Far from the electrode, a point charge experiences a potential arising from a wide area but each contribution is weak. (b) Close to the electrode, the point charge experiences a potential arising from a small area but each contribution is strong. Provided the point charge is in a certain range of values (and, specifically, where image charge effects can be ignored) the potential it experiences is largely independent of distance.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الدينية يواصل إقامة محاضراته الفقهية في صحن مرقد أبي الفضل العباس (عليه السلام)

أكاديمية التطوير الإداري تنظم دورة في أمن المعلومات واستخدام تطبيقات الذكاء الاصطناعي

بذكرى وفاتها.. قسم الشؤون الفكريّة يستعرض إصدارًا عن خطاب السيدة زينب (عليها السلام) وتأثيره

قسم الشؤون الدينية يقيم دورة تطويرية لمنتسبي قسمي الحزام الأخضر الشمالي والجنوبي

المزيد

الآخبار الصحية

طبيب يكشف أفضل مكمل غذائي لتحسين المزاج ودعم الصحة النفسية

دراسة جديدة تكشف أضرار الأطعمة الجاهزة على القلب ؟

6 أطعمة طبيعية تهدئ الزكام دون أدوية.. تعرف عليهم

ماذا يحدث لأعراض الزكام عند تناول الثوم بانتظام؟

المزيد

الآخبار التكنلوجية

ابتكار ثوري في بطاريات السيارات الكهربائية.. سعة أعلى 4 مرات

ماذا يحدث لجسمك عند شرب الماء الساخن يوميا؟

7 فوائد "خفية" لشرب شاي الكركديه كل يوم

دراسة تكشف قدرة الحيتان على سماع الأصوات منخفضة وعالية التردد من مسافة بعيدة

المزيد

مواضيع ذات صلة

Units

Names of quantities

Working galvanic cells

Electrolysis

Experimental techniques

The rate laws

The structure of the interface

Catalytic activity at surfaces

Mechanisms of heterogeneous catalysis

Mobility on surfaces

The rate of desorption

The rate of adsorption