Electrochemistry: Crash Course Chemistry #36

Aaah, the controlled flow of electrons, making possible laptops and phones and cars and pacemakers. Batteries, just like everything else in life, is just chemistry raised to the power of awesome. The kind of chemistry that happens inside of a battery is called electrochemistry because it involves reactions that produce or consume free electrons.

This section introduces the concept of batteries and electrochemistry.

Introduction to Batteries

• Batteries are devices that use electrochemistry to produce or consume free electrons.

• Electrochemistry involves reactions that produce or consume free electrons.

• The controlled flow of electrons in batteries enables the functioning of various electronic devices.

Specifically, they are oxidation or redox reactions, the ones where electrons are exchanged. I've told you about redox reactions before and if you haven't seen that episode yet, you should probably go watch that before you watch this. Don't worry, I will still be here when you get back. Now, when the flow of electrons in these kinds of reactions are sent through a conductor

This section explains how oxidation or redox reactions occur in batteries.

Oxidation and Redox Reactions

• Batteries involve oxidation or redox reactions where electrons are exchanged.

• Redox reactions involve both oxidation (loss of electrons) and reduction (gain of electrons).

• When the flow of electrons in these reactions passes through a conductor, it can be used to do work.

[like a piece of metal,

it can be used to do all sorts of work. Like, for example, this kind of work. The amount of work that can be done depends on how strong the push or pull on electrons is between the two reactants. This is the reaction's electrical potential,

but to its friends, it's known simply as voltage.]

This section discusses how the flow of electrons through a conductor can be used to do work and introduces the concept of voltage.

Work and Voltage

• When the flow of electrons passes through a conductor, it can be utilized to perform various types of work.

• The amount of work that can be done depends on the strength of the push or pull on electrons between the two reactants.

• This push or pull is known as the reaction's electrical potential, which is commonly referred to as voltage.

[Basically, if the voltage is high, each electron can do a lot more work than if the voltage is low. Many of the wonderful things in our modern lives are based on one simple premise: putting a device between the two halves of just such a reaction; the half that donates electrons,

and the half that accepts them.]

This section explains how higher voltage allows each electron to do more work and highlights how devices are placed between two halves of a redox reaction.

Higher Voltage and Work

• A higher voltage allows each electron to perform more work compared to lower voltages.

• Many modern technologies rely on placing a device between two halves of a redox reaction.

• One half donates electrons while the other half accepts them, allowing for useful applications.

[By harnessing that energy, a lot of the coolest things you've done today, up to and including watching this episode

of Crash Course Chemistry, has been made possible. Part of what makes redox reactions so powerful,

and powerfully excellent, is that they are complicated. Because in each reaction, there's at least

two things going on:]

This section emphasizes how harnessing energy from redox reactions enables various activities and highlights their complexity.

Harnessing Energy from Redox Reactions

• Harnessing energy from redox reactions enables the functioning of many everyday activities and technologies.

• Redox reactions are powerful and complex because they involve at least two simultaneous processes.

there's the part of the reaction where the electrons are being released and another part where they're being eagerly demanded. So when we deal with electrochemistry, we usually think of reactions in terms of half reactions. Let's start with a typical redox reaction that happens in this alkaline battery as an example.

This section introduces the concept of half reactions in electrochemistry and provides an example using an alkaline battery.

Half Reactions in Electrochemistry

• In electrochemistry, reactions are often considered in terms of half reactions.

• Half reactions involve the release or demand for electrons.

• An example is provided using a typical redox reaction that occurs in an alkaline battery.

[In here elemental zinc is going to react with manganese dioxide, also known as manganese four oxide, to produce manganese three oxide

and zinc oxide. When you break this down into half reactions, first you have elemental zinc with an oxidation number of 0 being oxidized to zinc 2 ion. At the same time manganese 4 is being reduced

to manganese 3.]

This section explains a specific redox reaction occurring in an alkaline battery involving elemental zinc and manganese dioxide.

Redox Reaction Example: Alkaline Battery

• In an alkaline battery, elemental zinc reacts with manganese dioxide (manganese four oxide) to produce manganese three oxide and zinc oxide.

• Breaking down this reaction into half reactions:

• Elemental zinc (oxidation number 0) is oxidized to form zinc 2 ions.

• Manganese four ions are reduced to form manganese three ions.

When we balance the half reactions, we see that two electrons are released during the oxidation of each zinc atom, and one electron is consumed by each manganese 4 atom. The water and hydroxide ions, by the way, come from a solution of potassium hydroxide. Which is a basic, or alkaline compound. Which is why we call these things alkaline batteries.

This section discusses balancing the half reactions in the redox reaction of an alkaline battery and explains the source of water and hydroxide ions.

Balancing Half Reactions in Alkaline Batteries

• Balancing the half reactions reveals that two electrons are released during the oxidation of each zinc atom, while one electron is consumed by each manganese four ion.

• Water and hydroxide ions come from a solution of potassium hydroxide, which is a basic (alkaline) compound.

• This explains why these batteries are called alkaline batteries.

[Now if each of these half reactions occurred in contact with the other one, they'd just spontaneously go to equilibrium releasing energy as a bunch of heat which wouldn't be very helpful. So batteries are designed to harness that energy by isolating the half reactions from each other. This allows excess electrons to build up in

the negative terminal, called the cathode,

while an electron vacuum of sorts occurs in

the positive terminal, the anode.

Electrons can then cross from one half reaction

to the other only when we connect the cathode and anode

of the battery via conductors. So current can be used to do work.

Which I can do by licking this 9-volt battery.]

This section explains how batteries isolate their half reactions to harness energy effectively.

Isolating Half Reactions in Batteries

• If both half reactions occurred together without isolation, they would reach equilibrium and release energy as heat, which is not useful.

• Batteries are designed to isolate the half reactions from each other to harness the energy effectively.

• This isolation allows excess electrons to accumulate in the negative terminal (cathode) while creating an electron vacuum in the positive terminal (anode).

• Electrons can cross from one half reaction to the other only when the cathode and anode of the battery are connected via conductors, allowing current to be used for work.

In these batteries, the zinc is in the center surrounded by a layer of cellulose that allows ions to pass through. The manganese oxide is in the outer layer that surrounds the zinc core, but the cellulose barrier doesn't allow the zinc and manganese to mix. Alkaline batteries are a type of galvanic cell.

This section describes how alkaline batteries are structured and explains their classification as galvanic cells.

Structure of Alkaline Batteries

• Alkaline batteries have a structure where zinc is at the center surrounded by a layer of cellulose that permits ion passage.

• The outer layer consists of manganese oxide surrounding the zinc core.

• The cellulose barrier prevents mixing between zinc and manganese.

• Alkaline batteries belong to a category known as galvanic cells.

[Which is generally defined as an apparatus that generates electrical energy from a redox reaction. Here's another example of a galvanic cell, one where the interesting part is the flow

of whole ions instead of the flow of electrons. In this case, wires connect metal rods that

are suspended in solution.]

This section provides further explanation about galvanic cells and introduces an example involving ion flow

New Section

This section explains the setup of an electrochemical cell and the concept of half reactions.

Setting Up the Cell

• The cell needs to be set up under the same conditions to ensure accurate voltage measurements.

• The temperature should be 25 degrees Celsius and the solutions should be 1 molar.

• The half reactions show that zinc is oxidized and copper is reduced.

New Section

This section discusses standard reduction potentials and how they are measured relative to hydrogen gas.

Standard Reduction Potentials

• All standard reduction potentials are measured relative to the reduction of hydrogen ions to hydrogen gas, which is set at zero.

• Copper has a standard reduction potential of +0.34 volts compared to hydrogen.

• Zinc has a standard reduction potential of -0.76 volts compared to hydrogen.

New Section

This section explains how to convert a reduction half reaction to oxidation and determine the oxidation potential.

Converting Reduction Potential

• When converting a reduction half reaction to oxidation, reverse the sign of the voltage.

• The -0.76 volts for zinc's reduction potential becomes +0.76 volts for its oxidation potential.

New Section

This section introduces the concept of standard cell potential and its relation to equilibrium constant.

Standard Cell Potential

• The standard cell potential is the sum of the standard potentials of both half reactions.

• In this case, it would be 1.1 volts.

• The electrical potential of a redox reaction is related to its equilibrium constant.

New Section

This section explains how positive and negative voltages indicate whether a reaction will proceed forward or backward.

Voltage and Reaction Direction

• A positive voltage indicates that the reaction will spontaneously go forward under standard state conditions.

• A negative voltage means the reaction will proceed backward.

• Reactions with positive voltages are used in battery cells to release energy.

New Section

This section discusses electroplating as an example of a non-spontaneous redox reaction.

Electroplating

• Electroplating is a non-spontaneous electrochemical process used to plate objects with a metal coating.

• An object is immersed in a solution containing excess ions of the coating metal.

• When an electric current is applied, atoms of the coating metal are deposited on the object's surface.

New Section

This section explains electrolysis and its various applications.

Electrolysis

• Electrolysis uses electricity to break down molecules in a solution so that metal atoms can be deposited on a surface.

• It is used for processes like coating jewelry or flatware with gold or silver, refining metals, separating mixtures of metal ions, and converting water into hydrogen gas and oxygen.

New Section

This section highlights the impact of chemistry and electrochemistry in our daily lives.

Impact of Chemistry

• Chemistry plays a significant role in our daily lives, from materials around us to electrical devices that depend on electrochemical reactions.

• Understanding electrochemistry helps us comprehend how batteries work and enables processes like electrolysis and electroplating.

New Section

The conclusion summarizes key concepts covered in the video.

Conclusion

• Electrochemical reactions involve redox reactions described through half reactions.

• Alkaline batteries use galvanic cells to generate voltage.

• Standard reduction potential measures how much voltage can be generated by a half reaction.

• Standard cell potential is the sum of the standard potentials of both half reactions.

• Electrolysis and electroplating are examples of non-spontaneous redox reactions.

• Chemistry and electrochemistry have a significant impact on our daily lives.

The timestamps provided in the summary may not be exact due to limitations in processing natural language. Please refer to the original transcript for precise timestamps.