How Does a Battery Work? Alkaline Batteries - AP Chemistry

Summary

This video script delves into alkaline batteries, the most prevalent single-use batteries known for their longevity and high energy density despite being non-rechargeable. It explains the galvanic cell mechanism, highlighting the redox reaction between zinc at the anode and manganese dioxide at the cathode facilitated by a basic electrolyte. The script also details the half-reactions, the balancing process for a basic solution, and the overall cell potential of 1.45 volts. It concludes with the practical application of these batteries and how they can be combined to form higher voltage batteries.

Takeaways

• 🔋 Alkaline batteries are the most common type of single-use batteries known for their long-lasting and high energy density.
• ❌ These batteries are not rechargeable, as the chemical reaction within them cannot be reversed to an electrolytic cell.
• 💰 Alkaline batteries are relatively inexpensive due to the simplicity of their construction and the materials used.
• 🔬 They function as a galvanic or voltaic cell, utilizing a spontaneous redox reaction to produce energy, indicated by a negative Gibbs free energy and a positive electrochemical cell potential.
• 🔬 The name 'alkaline battery' comes from the use of a basic electrolyte, which has a pH greater than seven.
• 🔄 The redox reaction in an alkaline battery occurs between the anode (zinc) and the cathode (manganese dioxide), separated by an ion-conducting separator.
• ⚡ The anode undergoes oxidation where zinc metal loses electrons, and the cathode undergoes reduction where manganese dioxide gains electrons.
• 🔩 Graphite powder is often mixed in the cathode to enhance electrical conductivity and prevent corrosion.
• 🧪 The half-reactions are balanced as if in an acidic solution and then adjusted to a basic solution to reflect the actual conditions in the battery.
• 🔋 The standard cell potential of an alkaline battery is approximately 1.5 volts, which can vary based on factors like substance purity and temperature.
• 🔋 Alkaline batteries cease to function when the reactants, zinc or manganese dioxide, are depleted, leading to a zero cell potential.

Q & A

What are alkaline batteries?

Alkaline batteries are the most common type of single-use batteries known for their relatively long life and high energy density. They are not rechargeable, meaning the chemical reaction within them cannot be reversed to restore their charge.

Why are alkaline batteries considered a type of galvanic or voltaic cell?

Alkaline batteries are considered galvanic or voltaic cells because they use a spontaneous or thermodynamically favorable redox reaction to produce energy, with a Gibbs free energy value less than zero and an electrochemical cell potential greater than zero.

What is the role of the basic electrolyte in an alkaline battery?

The basic electrolyte in an alkaline battery, typically potassium hydroxide, creates a pH greater than seven. This electrolyte facilitates the redox reaction between the anode and cathode, which is essential for the battery's operation.

How does the physical separation of anode and cathode in an alkaline battery contribute to its functionality?

The anode and cathode are separated to prevent the spontaneous reaction that would occur if they were in direct contact. This separation allows the battery to store energy and control the reaction, enabling it to proceed only when a conductive path is established.

What happens at the anode in an alkaline battery?

At the anode, zinc metal reacts with potassium hydroxide in an oxidation reaction, losing electrons. This process is part of the redox reaction that generates electricity in the battery.

What occurs at the cathode in an alkaline battery?

At the cathode, manganese dioxide (MnO2) gains electrons in a reduction reaction. This process is facilitated by the addition of graphite powder, which enhances the electrical conductivity and helps in the reduction of manganese dioxide.

Why is graphite powder mixed in the cathode of an alkaline battery?

Graphite powder is mixed in the cathode to improve conductivity and facilitate the electron transfer to the manganese dioxide. Graphite is chosen because it conducts electricity well and does not corrode easily like most metals.

How are the half-reactions balanced in an alkaline battery?

The half-reactions are first balanced as if they were in an acidic solution, then adjusted to a basic solution by adding hydroxides to neutralize the hydrogen ions. This process helps to balance the charges and allows for the combination of the half-reactions to form the overall battery reaction.

What is the standard cell potential of an alkaline battery?

The standard cell potential of an alkaline battery is approximately 1.5 volts, which is derived from the sum of the oxidation and reduction potentials of the half-reactions involved in the battery's chemistry.

Why does an alkaline battery eventually die?

An alkaline battery dies when there is insufficient reactant material, such as zinc or manganese dioxide, to continue the redox reaction. At this point, the system reaches equilibrium, and the cell potential drops to zero, signaling the end of the battery's useful life.

How can multiple alkaline batteries be combined to create a higher voltage battery?

Six 1.5-volt alkaline batteries can be connected in series to create a 9-volt battery. This is achieved by stacking the batteries so that the positive terminal of one battery connects to the negative terminal of the next, thus multiplying the voltage while keeping the current capacity the same.

Outlines

00:00

🔋 Understanding Alkaline Batteries

Alkaline batteries, the most common type of single-use batteries, are highlighted for their relatively long life and high energy density. Despite being non-rechargeable due to the irreversible nature of their electrochemical reactions, they are cost-effective. These batteries function as galvanic or voltaic cells, utilizing spontaneous redox reactions with a negative Gibbs free energy to produce electricity. Characterized by a basic electrolyte, alkaline batteries have a pH greater than seven. The video explains the internal structure of an alkaline battery, showing the redox reaction occurring between the anode (zinc) and the cathode (manganese dioxide), separated by an ion-conducting separator. The necessity of a conductive path for electron flow to initiate the reaction is emphasized, as is the role of graphite powder in the cathode to facilitate electron transfer without corrosion. The half-reactions for zinc and manganese dioxide are detailed, explaining the process of balancing these reactions in an acidic solution before adjusting for the basic environment of the battery.

05:01

🔬 Electrochemical Reactions in Alkaline Batteries

This segment delves into the electrochemical reactions within alkaline batteries, focusing on the balancing of half-reactions to determine the overall cell potential. The oxidation half-reaction of zinc and the reduction half-reaction of manganese dioxide are examined, with the addition of water and hydroxides to balance the reactions in a basic solution. The video clarifies that the steps taken to balance the reactions are strategic and do not represent the actual reaction steps. The final reaction equations are presented, showing the formation of zinc oxide and water in the oxidation process, and manganese oxide and hydroxides in the reduction process. The standard cell potential is calculated to be approximately 1.5 volts, which can vary based on factors like substance purity and temperature. The video concludes with a discussion on how alkaline batteries are used in devices, the role of the potassium hydroxide electrolyte, and how six individual 1.5-volt batteries can be combined to form a 9-volt battery.

Keywords

💡Alkaline batteries

Alkaline batteries are a type of single-use battery that are commonly used due to their long-lasting nature and high energy density. They are not rechargeable, meaning the chemical reaction within them cannot be reversed to restore their charge. In the video, alkaline batteries are described as a galvanic cell, utilizing a spontaneous redox reaction to produce electricity. The term 'alkaline' refers to the basic electrolyte used, which has a pH greater than seven.

💡Galvanic cell

A galvanic cell, also known as a voltaic cell, is a device that produces electrical energy through a spontaneous chemical reaction. In the context of the video, an alkaline battery is a type of galvanic cell where the reaction is thermodynamically favorable, indicated by a negative Gibbs free energy and a positive electrochemical cell potential.

💡Redox reaction

Redox reactions involve the transfer of electrons between chemical species, leading to changes in their oxidation states. In the video, the redox reaction in an alkaline battery occurs between the anode (zinc metal) and the cathode (manganese dioxide), with the zinc being oxidized and the manganese dioxide being reduced. This reaction is fundamental to the battery's ability to produce electricity.

💡Anode

The anode is the electrode in an electrochemical cell where oxidation occurs. In the video, the anode is made of zinc, which reacts with the potassium hydroxide in the electrolyte, losing electrons. This process is crucial for the flow of electrons that powers devices like light bulbs or motors.

💡Cathode

The cathode is the electrode in an electrochemical cell where reduction occurs. In the video, the cathode contains manganese dioxide, which gains electrons from the anode. The reduction of manganese dioxide is part of the battery's redox reaction, contributing to the flow of electrons that generate electricity.

💡Electrolyte

An electrolyte is a substance that conducts electricity when dissolved in a solution, typically due to the presence of ions. In the video, potassium hydroxide serves as the basic electrolyte in alkaline batteries, facilitating the flow of ions and maintaining the electrochemical reaction necessary for electricity production.

💡Oxidation

Oxidation is a chemical process where a substance loses electrons. In the context of the video, zinc at the anode undergoes oxidation, turning into zinc oxide and releasing electrons. This process is a key part of the battery's electrochemical reaction.

💡Reduction

Reduction is a chemical process where a substance gains electrons. In the video, manganese dioxide at the cathode is reduced, changing its oxidation state from +4 to +3. This gain of electrons is part of the battery's redox reaction, which is essential for generating an electric current.

💡Cell potential

Cell potential, or electromotive force, is the electrical potential difference across the terminals of a battery or a cell. In the video, the standard cell potential of an alkaline battery is discussed as being approximately 1.5 volts, which is a measure of the battery's ability to convert chemical energy into electrical energy.

💡Separator

A separator in a battery is a material that prevents the physical mixing of the anode and cathode while allowing the flow of ions. In the video, the separator allows hydroxide ions to flow between the anode and cathode, maintaining a balanced charge and preventing the buildup of charge that would otherwise render the battery inoperative.

💡Standard cell potential

Standard cell potential refers to the potential of a cell under standard conditions, typically at 25 degrees Celsius and with a concentration of 1M for the electrolyte. In the video, the standard cell potential of an alkaline battery is calculated to be 1.45 volts, which is a theoretical value that can vary with actual conditions such as temperature and purity of the substances.

Highlights

Alkaline batteries are the most common type of single-use batteries.

They have high energy density but are not rechargeable.

Alkaline batteries are relatively inexpensive due to their non-rechargeable nature.

They function as a galvanic cell, using a spontaneous reaction to produce energy.

The Gibbs free energy value for alkaline batteries is less than zero, indicating a favorable reaction.

The electrochemical cell potential is greater than zero in alkaline batteries.

Alkaline batteries utilize a redox reaction for electron transfer and electricity production.

The term 'alkaline' refers to the basic electrolyte with a pH greater than seven.

The anode and cathode are separated to prevent unwanted spontaneous reaction.

Zinc at the anode reacts with potassium hydroxide in an oxidation process.

Manganese dioxide at the cathode is reduced, gaining electrons from the anode.

Graphite powder in the cathode aids in conducting electricity without corrosion.

Half reactions are balanced as if in an acidic solution, then adjusted for a basic solution.

The oxidation half reaction involves zinc turning into zinc oxide with a potential of +1.29 volts.

The reduction half reaction involves manganese dioxide turning into manganese oxide with a potential of 0.16 volts.

The total standard cell potential is approximately 1.5 volts.

The battery dies when reactants like zinc or manganese dioxide are depleted.

Alkaline batteries can be combined to form higher voltage batteries, such as a 9-volt battery from six 1.5-volt batteries.

Transcripts

these two batteries here

are called alkaline batteries alkaline

batteries are the most common type of

single-use batteries

they last relatively long have high

energy density

but they are not rechargeable this means

that the reaction cannot be reversed

by turning it back into an electrolytic

cell

but that makes it relatively cheap

an alkaline battery is a type of a

galvanic cell

or voltaic cell because it uses a

spontaneous

or thermodynamically favorable reaction

to produce

energy this means that the gibbs free

energy value

is less than zero and the

electrochemical

cell potential is greater than zero

this uses a redox reaction which allows

the transfer of electrons

to produce electricity and the reason

why it's called

an alkaline battery is because there's a

basic electrolyte

that makes the ph greater than seven

so this is a diagram right here if we

look at the diagram we can see that the

redox reaction

happens between the anode and the

cathode

and the anode and cathode are separated

on purpose so the reaction does not

proceed

unless a wire or some sort of conductive

material is placed on the outside to

connect them

and this is done on purpose because

let's say there was no

wall separating the two

and the reaction would just happen and

the

battery would be dead so this allows the

battery to store energy

and have the reaction proceed whenever

it is needed

but stop whenever it is not needed

if we connect the positive and negative

terminals

then the electron can now flow

and the redox reaction can occur like

this

at the anode there is zinc metal

which reacts with potassium hydroxide

in an electrolyte form meaning it's

aqueous and this is the basic

electrolyte we were talking about

oxidation always happens at the anode so

the zinc is

oxidized and it will lose electrons

the electrons leave the negative

terminal

where the anode is connected to

and it'll go to the positive

so the electrons go from negative to

positive

and into the cathode at the cathode

there's manganese iv oxide

also called manganese dioxide

reduction always happens at the cathode

so the manganese dioxide is reduced

and gains the electrons coming from the

anode

just a side note there's often going to

be graphite powder

mixed in the cathode to help conduct

electricity

or in other words to help the electron

transfer

to the manganese to help reduce it

graphite is one of the rare covalent

networks that

will conduct electricity and that's

super useful because it doesn't easily

corrode like most metals so it's useful

in batteries

let's take a look at the half reactions

zinc is turned into zinc oxide and the

oxidation

state of zinc as a pure metal is zero

and it turns into positive two

manganese four oxidises turn into

manganese

three oxide so the oxidation state that

i just mentioned

is from plus four to plus three

so in order to balance

the half reactions we need to first

balance

them as if they were in acidic solution

and then add hydroxides to turn it into

a basic solution

so note that these steps do not actually

represent

the real steps of the reaction it's just

a strategy to help balance it

first the manganese is balanced right

here so there are two

on both sides and then we add water

to balance out the oxygens

and we add hydrogen ions or protons

to help balance out the hydrogens that

we just have

from the water and then

we add hydroxides on both sides

to cancel out the hydrogens

because this is actually a basic

solution

we combine the hydrogens and hydroxides

on both sides to form water as part of

our step

again this is not the actual reaction

we're just

using this to help balance the reaction

and then we can cancel on both sides

the water and we get the final reaction

right here

we add the electrons on both sides

so note that there are two electrons in

both of the half reactions so we do not

need to multiply

by any coefficients when

applying the full reaction

the oxidation half reaction right here

the zinc reacts with two hydroxides to

form zinc

oxide and water and the

oxidation potential is positive 1.29

volts

but usually you'll see it in another

form

which is that the reduction hap

potential is negative 1.29 volts

in the reduction half half reaction

two manganese four oxides react with

water to form manganese

three oxide and two hydroxides

and here the reduction potential

is 0.16 volts

and the overall reaction we can just add

all of these

and we get that the cell potential

the total standard cell potential is

positive

1.45 volts which is

which is approximately equal to 1.5

volts

of course this is just the standard cell

potential so it can change depending on

a lot of factors like the purity of the

substances

the temperature etc

so let's take a look at this diagram

again we can see that the battery will

eventually die

when there is not enough of the

reactants

zinc or manganese dioxide to continue

the reaction

in other words the system will be at

equilibrium

and the cell potential or voltage will

be zero

the potassium hydroxide electrolyte

is not in the total equation because the

hydroxide is being consumed

right here and produced

in both half reactions if we look at the

diagram

the ion conducting separator allows the

hydroxide ions to flow

to maintain a balanced charge so charge

doesn't build

up it's kind of like

a salt bridge in a concentration cell

but using this process a machine such as

a light bulb or a motor can be put

in between the current

and it'll be powered by the electricity

six 1.5 volt batteries can be put

together

to make the 9 volt battery we saw

earlier

and that's it for the alkaline battery

thanks for watching