Vaia - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
Americas
Europe
One thing that makes the periodic table so special is that each of the elements is different in one way or another. Although there are trends in some of their properties, they all differ ever so slightly. A consequence of this is that they all have different reactivities. We can see this in terms of how easily they give up…
Explore our app and discover over 50 million learning materials for free.
Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken
Jetzt kostenlos anmeldenNie wieder prokastinieren mit unseren Lernerinnerungen.
Jetzt kostenlos anmeldenOne thing that makes the periodic table so special is that each of the elements is different in one way or another. Although there are trends in some of their properties, they all differ ever so slightly. A consequence of this is that they all have different reactivities. We can see this in terms of how easily they give up their electrons - or in other words, how easily they are oxidised. The electrochemical series is a handy form of sorting species in this way, and is the basis behind redox reactions, fuel cells, and batteries.
At the start, we put across the idea that some elements are better at giving up their electrons than others. This is a fundamental principle of chemistry, and is the basis behind all redox reactions. To explore this in more detail, we need to look at the electrochemical series. But first, you need a bit of background knowledge. For that, we'll start by learning about half-cells, electrochemical cells, and standard electrode potential.
Imagine putting a rod of zinc in a solution of zinc ions. You eventually form an equilibrium, in which some of the zinc atoms give up their electrons to form zinc ions. Here's the equation. You'll notice that it is conventional to write the ions and electrons on the left-hand side and the metal atom on the right:
The zinc ions move into solution whilst the released electrons gather on the rod, giving the rod a negative charge. This creates a potential difference between the zinc rod and the zinc ion solution, known as an electrode potential. The exact position of this equilibrium and the exact potential difference of the system depends on the reactivity of zinc and how easily it gives up its electrons.
The more negative a potential difference, the further to the left the equilibrium lies, and the more easily a metal gives up its electrons. For example, a metal that creates a potential difference of -1.2 V gives up its electrons more easily than a metal that creates a difference of -0.3 V.
Now, consider what would happen if you put a rod of copper in a solution of copper ions. Some of the copper atoms react, giving up their electrons to form copper ions. Once again, you'll eventually form an equilibrium. But copper is less reactive than zinc and is not so good at giving up its electrons - we can say that copper is a worse reducing agent. It means that the potential difference of this copper system is less negative than the potential difference of the zinc system. We call the system created by putting a metal in a solution of its own ions a half -cell.
Reducing agents are themselves oxidised. This means that a better reducing agent is oxidised more easily.
Finally, take a moment to think about what would happen if you joined the zinc half-cell and the copper half-cell together with a wire and a salt bridge. Zinc is a better reducing agent than copper - it is more reactive and gives up its electrons more easily. This means that it has a more negative potential difference than copper does. It creates an overall potential difference between the two cells, which we can also call an electrode potential, showing the difference in how readily the two metals give up their electrons. The potential difference is measured by a voltmeter connected to the system.
The combination of two half-cells is known as an electrochemical cell. It is based on nothing more than simple redox reactions. Because zinc has a more negative potential difference than copper, there is a greater build-up of electrons on the zinc rod. If we allow these electrons to flow, then they will travel through the wire from zinc, the better reducing agent, to copper, the worse reducing agent. Meanwhile, positive ions from the solution will flow across the salt bridge in the same direction to balance the charge. Zinc atoms turn into zinc ions, losing electrons; copper ions turn into copper atoms, gaining electrons. Here are the two equations:
In general, electrons always travel from the better reducing agent (the more reactive metal, which gives up its electrons more easily) to the worse reducing agent (the less reactive metal, which is worse at giving up its electrons).
We know that if you put a metal in solution, it forms an equilibrium of metal atoms and metal ions. This creates a potential difference, the value of which depends on the position of the equilibrium. We can't directly measure the potential difference generated by a single half-cell. However, we can measure the potential difference generated when you connect two half-cells together in an electrochemical cell. If we record the potential differences generated when you connect a whole range of different half-cells to one particular reference half-cell, we can create a table comparing these values, and thus rank the metals from the most reactive (the best reducing agent) to the least reactive (the worst reducing agent).
In fact, scientists have done this. The reference half-cell used is the hydrogen electrode. We call the potential difference between a half-cell and the reference hydrogen electrode under standard conditions the cell's standard electrode potential. It is a measurement of the element's reducing ability.
Standard electrode potential, E°, is the potential difference generated when a half-cell is connected to a hydrogen half-cell under standard conditions. It is also known as electromotive force or standard reduction potential.
Standard conditions are 298 K, 1.00 mol dm-3 and 100 kPa. You can look at both the hydrogen electrode and the importance of standard conditions in Electrode Potential.
We represent standard electrode potentials (E°) using half equations involving the element and its ions. Note the following:
Here is the standard electrode potential for zinc, Zn:
The standard electrode potential value is negative. This means that zinc is a better reducing agent than hydrogen and is more easily oxidised.
Amassing the standard electrode potentials of different elements creates the electrochemical series.
The electrochemical series is a list of elements ordered by their standard electrode potentials. It tells us how easily each element is oxidised compared to a reference half-cell, the hydrogen electrode.
The electrochemical series is the basis behind all kinds of modern fuel cells and batteries. But before we look at these applications, let's take a look at the electrochemical series itself in the form of a table.
The moment you've been waiting for - here's the electrochemical series. We've shown it as a table of different half-cells and their standard electrode potentials.
Note that the electrochemical series can either run from positive to negative, or negative to positive. Here, we've shown it from negative to positive, with the most-easily oxidised element (lithium, Li) at the top. This means that lithium is the strongest reducing agent.
We've learned what the electrochemical series is. Now let's consider some of its applications.
The electrochemical series is a list of elements ordered by their standard electrode potentials. It gives us important information about which substances are good oxidising agents and which ones are good reducing agents, and also helps us predict the direction of redox reactions.
The electrochemical series is a list of elements that are ordered by their standard electrode potentials.
In an electrochemical series, the species are arranged in order of their standard electrode potentials. The electrochemical series can either run from positive to negative, or negative to positive.
The electrochemical series can be used to identify good oxidising and reducing agents, calculate the cell potential of electrochemical cells, and predict the direction of redox reactions.
Consider zinc and copper. Zinc is better at giving up its electrons than copper and so has a more negative electrode potential: its standard electrode potential is -0.76 V, compared to copper's +0.34 V. In an electrochemical series running from negative to positive, zinc is therefore found higher up in the series than copper.
How would you like to learn this content?
94% of StudySmarter users achieve better grades.
Sign up for free!94% of StudySmarter users achieve better grades.
Sign up for free!How would you like to learn this content?
Free chemistry cheat sheet!
Everything you need to know on . A perfect summary so you can easily remember everything.
Be perfectly prepared on time with an individual plan.
Test your knowledge with gamified quizzes.
Create and find flashcards in record time.
Create beautiful notes faster than ever before.
Have all your study materials in one place.
Upload unlimited documents and save them online.
Identify your study strength and weaknesses.
Set individual study goals and earn points reaching them.
Stop procrastinating with our study reminders.
Earn points, unlock badges and level up while studying.
Create flashcards in notes completely automatically.
Create the most beautiful study materials using our templates.
Sign up to highlight and take notes. It’s 100% free.