How Does a Battery Work? Alkaline Batteries - AP Chemistry
Summary
TLDRThis 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
🔋 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.
🔬 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.
Mindmap
Keywords
💡Alkaline batteries
💡Galvanic cell
💡Redox reaction
💡Anode
💡Cathode
💡Electrolyte
💡Oxidation
💡Reduction
💡Cell potential
💡Separator
💡Standard cell potential
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
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