Electrolytic Cell: Videos & Practice Problems

An electrolytic cell is a type of electrochemical cell that operates through electrolysis, using external electrical energy to drive non-spontaneous chemical reactions. Unlike galvanic cells, which generate electricity, electrolytic cells consume electricity and require a battery to initiate redox reactions. The cathode, where reduction occurs, is negatively charged, while the anode, where oxidation happens, is positively charged. This is due to the non-spontaneous nature of the reactions, necessitating a battery to force electron flow against the natural repulsion of like charges. Electrolytic cells are commonly found in lithium batteries and rechargeable batteries. The standard cell potential for non-spontaneous reactions in an electrolytic cell is negative, indicating that the Gibbs free energy change is greater than zero, the standard entropy change is less than zero, the equilibrium constant (K) is less than one, and the reaction quotient (Q) is less than K, all of which are indicative of non-spontaneity.

The Electrolytic Cell

An electrolytic cell is a type of electrochemical cell that operates through non-spontaneous reactions, utilizing a process known as electrolysis. In this context, electrolysis refers to chemical reactions that require an external source of electrical energy to proceed. Unlike spontaneous reactions, which occur naturally, electrolytic cells need this additional energy input to function effectively. Common examples of electrolytic cells include lithium batteries and rechargeable batteries, which are prevalent in everyday technology.

Regardless of the type of electrochemical cell—whether it is a spontaneous galvanic (or voltaic) cell or a non-spontaneous electrolytic cell—the fundamental roles of the electrodes remain consistent. The cathode is always the site of reduction, where gain of electrons occurs, while the anode is the site of oxidation, where loss of electrons takes place. This relationship can be summarized as follows: cathode = reduction and anode = oxidation. Understanding these principles is crucial for grasping the underlying mechanisms of electrochemical processes.

Electrolytic Cell Example

In electrochemical cells, the processes of reduction and oxidation are fundamental to their operation. In a galvanic cell, which generates electrical energy from spontaneous chemical reactions, reduction occurs at the cathode. This is the site where electrons are accepted, leading to a decrease in oxidation state. Conversely, oxidation, which involves the loss of electrons, takes place at the anode.

In electrolytic cells, which require an external power source to drive non-spontaneous reactions, the same principles apply. Reduction still occurs at the cathode, while oxidation occurs at the anode. This consistency across different types of electrochemical cells is crucial for understanding their functioning. Therefore, regardless of whether the cell is galvanic or electrolytic, it is essential to remember that reduction always takes place at the cathode and oxidation at the anode.

Electrolytic Cell Components

Electrolytic cells and galvanic cells share similar components, yet they function quite differently due to their distinct roles in electrochemical reactions. The primary distinction lies in their energy dynamics: electrolytic cells consume electrical energy, requiring an external power source, such as a battery, to drive the reaction. In contrast, galvanic cells generate electricity from spontaneous chemical reactions, often measured with a voltmeter.

In an electrolytic cell, the stored electrical energy from the battery is converted into chemical energy, facilitating a redox reaction that is non-spontaneous. This means that the reaction does not occur naturally and must be forced to proceed. Consequently, the cathode in an electrolytic cell is negatively charged, while the anode is positively charged. This configuration is crucial because like charges repel; thus, electrons from the anode, which is losing electrons (oxidation), are pushed towards the cathode, where reduction occurs.

For example, at the anode, copper undergoes oxidation, transforming from solid copper to copper ions in solution, represented as:

Cu (s) → Cu²⁺ (aq) + 2e^-

Simultaneously, at the cathode, tin ions are reduced to solid tin, as shown in the following reaction:

Sn²⁺ (aq) + 2e^- → Sn (s)

The overall reaction, after canceling out the electrons, can be summarized as:

Cu (s) + Sn²⁺ (aq) → Cu²⁺ (aq) + Sn (s)

Additionally, the salt bridge plays a vital role in maintaining charge balance by allowing the movement of ions. Negative ions migrate towards the anode to neutralize the buildup of positive copper ions, while positive ions move towards the cathode to support the flow of electrons.

Understanding these key differences is essential for grasping the operational principles of electrolytic cells and their applications in electrochemistry.

Electrolytic Cell Components Example

An electrolytic cell is a type of electrochemical cell that requires an external power source to drive a non-spontaneous chemical reaction. In this setup, the cathode is positively charged, which is a key distinction from a galvanic cell where the cathode is negatively charged. Despite this difference, the fundamental processes at the electrodes remain consistent across both types of cells.

At the cathode of an electrolytic cell, reduction occurs, leading to the plating out of material. This means that ions in the solution gain electrons and are deposited as solid material on the cathode surface. Conversely, the anode in an electrolytic cell is positively charged and is the site of oxidation, where material dissolves into the solution as electrons are released.

Unlike galvanic cells, electrolytic cells do not utilize a salt bridge; instead, they rely on the external power source to maintain the flow of current and facilitate the reactions. The anode's role in oxidation and the cathode's role in reduction are consistent features that help in understanding the operation of both electrolytic and galvanic cells.

Electrolytic Cells and Spontaneity

An electrolytic cell operates by driving non-spontaneous redox reactions, which require an external source of electricity to proceed. In this context, it is essential to understand the relationship between various thermodynamic variables and the spontaneity of the reactions involved.

For non-spontaneous reactions, the standard cell potential (\(E^\circ\)) is negative, indicating that the reaction does not occur naturally under standard conditions. This can be expressed mathematically as:

\(E^\circ < 0\)

Additionally, the change in standard Gibbs free energy (\(\Delta G^\circ\)) for these reactions is positive, which can be represented as:

\(\Delta G^\circ > 0\)

In terms of entropy, the change in the standard entropy of the universe (\(\Delta S_{universe}^\circ\)) is negative, indicating that the overall disorder decreases:

\(\Delta S_{universe}^\circ < 0\)

The equilibrium constant (\(K\)) for non-spontaneous reactions is less than 1, reflecting that the products are not favored at equilibrium:

\(K < 1\)

Furthermore, the reaction quotient (\(Q\)) must be greater than the equilibrium constant (\(K\)), reinforcing the idea that the reaction is not favored in the forward direction:

\(K < Q\)

These relationships highlight the interconnectedness of Gibbs free energy, entropy, equilibrium constants, and standard cell potential in understanding the behavior of electrolytic cells and their non-spontaneous nature.

Electrolytic Cells and Spontaneity Example

In electrochemistry, the standard cell potential (E_cell^°) is a crucial indicator of the spontaneity of a redox reaction. When the standard cell potential is negative, as in the case of E_cell^° = -0.54 volts, it signifies that the reaction is non-spontaneous. This means that the reaction will not proceed in the forward direction under standard conditions.

For non-spontaneous reactions, the equilibrium constant (K) is less than 1. This is because a negative standard cell potential indicates that the products of the reaction are less favored than the reactants at equilibrium. Therefore, the statement that the equilibrium constant value is greater than 1 is incorrect.

Additionally, non-spontaneous reactions do not produce electricity; instead, they consume it. This further confirms that the statement regarding the production of electricity is also false. In this context, the reaction quotient (Q) will be less than the equilibrium constant (K), reinforcing the idea that the system is not at equilibrium and that the forward reaction is not favored.

In summary, when the standard cell potential is negative, the correct interpretation is that the equilibrium constant (K) is less than 1, indicating a non-spontaneous reaction. Thus, the key takeaway is that a negative E_cell^° correlates with a non-spontaneous process, where K < 1 and Q < K.

If the overall redox reaction for an electrolytic cell is given below, what will happen to the mass of the cobalt electrode?
Co²⁺ (aq) + Cu (s) ⇌ Co (s) + Cu²⁺(aq)

• A. Its mass will increase. 
• B. Its mass will decrease. 
• C. Its mass will remain constant. 
• D. Not enough information is given.

Answer: (A)

Here’s what students ask on this topic:

Where does reduction occur in an electrolytic cell?

In an electrolytic cell, reduction occurs at the cathode. This is the electrode where positively charged ions, or cations, gain electrons and are reduced. The process of reduction involves the gain of electrons, which decreases the oxidation state of the substance. Since cations are attracted to the cathode, they migrate towards it, where they receive electrons from the power source that's driving the electrolytic process. This electron gain results in the reduction of the cations into a neutral state or a lower oxidation state. Remember, you can use the mnemonic "Red Cat" to help recall that Reduction occurs at the CAThode in an electrolytic cell.

What are some of the necessary components of an electrolytic cell?

An electrolytic cell is a device that drives a non-spontaneous chemical reaction through the application of electrical energy. The necessary components of an electrolytic cell include:

1. Electrodes: There are two electrodes, the anode and the cathode. The anode is the electrode where oxidation occurs, and electrons are given up to the power source. The cathode is where reduction takes place, and electrons from the power source are accepted.
2. Electrolyte: This is the medium that contains ions, which can be a liquid or a molten salt that conducts electricity. The electrolyte provides the ions that are necessary for the chemical reaction.
3. Power Source: A direct current (DC) power supply, such as a battery or rectifier, is needed to provide the energy to drive the non-spontaneous reaction.
4. Container: A vessel that holds the electrodes and the electrolyte, ensuring that the reaction can occur in a controlled environment.
5. Conducting Wires: These connect the electrodes to the power source, allowing the flow of electrons into and out of the electrolytic cell.
6. Salt Bridge (optional): In some cells, a salt bridge is used to maintain the electrical neutrality of the electrolyte solutions during the reaction process.

Understanding the function of each component is crucial for manipulating

What kind of reaction occurs in an electrolytic cell?

In an electrolytic cell, an electrochemical reaction that requires the input of electrical energy to proceed is carried out. This type of reaction is known as an electrolysis reaction. During electrolysis, an external voltage is applied to drive a non-spontaneous chemical reaction. This contrasts with galvanic or voltaic cells, where the reaction is spontaneous and generates electrical energy.

In an electrolytic cell, the anode is the positive electrode, and the cathode is the negative electrode. When the current is applied, positive ions (cations) move towards the cathode and gain electrons in a reduction reaction, while negative ions (anions) move towards the anode and lose electrons in an oxidation reaction. Common applications of electrolytic cells include the decomposition of water into oxygen and hydrogen gas, electroplating, and the production of chemicals like chlorine and sodium hydroxide.

Does the diagram above represent an electrolytic cell in which the reaction?

The question seems to be referring to a diagram that isn't visible in this context. However, I can explain what an electrolytic cell is and how you can identify one.

In an electrolytic cell, electrical energy is used to drive a non-spontaneous chemical reaction. This is the opposite of a galvanic or voltaic cell, where a spontaneous reaction generates electrical energy. To identify an electrolytic cell in a diagram, look for a few key components:

1. Power Source: An external battery or power supply is connected to two electrodes, indicating the need for an external electric current to induce the reaction.
2. Electrodes: There should be two electrodes, an anode and a cathode, typically labeled and placed in a solution (electrolyte). In an electrolytic cell, the anode is positive, and the cathode is negative, which is the reverse of a galvanic cell.
3. Electrolyte: This is the medium (usually a liquid) that contains ions which can move to carry electric charge between the electrodes.
4. Chemical Reaction: The diagram may also show a non-spontaneous reaction occurring at the electrodes, such as the decomposition of water into hydrogen and oxygen gases.

If the diagram includes these features, it likely represents an electrolytic cell. Remember, the key distinction