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.