Problem 74 - Advanced Problems in Physical Chemistry for Competitive Examinations

Question

Electrolytic cell is used to convert (a) Chemical energy to electrical energy (b) Electrical energy to chemical energy (c) Chemical energy to mechanical energy (d) Electrical energy to mechanical energy

Step-by-Step Solution

Answer

An electrolytic cell converts electrical energy to chemical energy, hence the correct answer is (b) Electrical energy to chemical energy.

Step 1: Understanding an Electrolytic Cell

An electrolytic cell is a type of cell that uses electrical energy to drive a non-spontaneous chemical reaction. This process is known as electrolysis. During electrolysis, an external voltage is applied to the electrodes in the cell to initiate the chemical reaction.

Step 2: Identifying the Type of Energy Conversion

Given that an electrolytic cell uses an external voltage, it takes electrical energy and converts it into chemical energy stored in the chemicals produced during the electrolysis reaction.

Step 3: Choosing the Correct Option

Since an electrolytic cell converts electrical energy to chemical energy, the correct answer is option (b) Electrical energy to chemical energy.

Key Concepts

Electrolysis

Electrolysis is a fascinating chemical process where electricity is the driving force behind a transformation. This technique splits compounds, often dissolved in water or melted, into their constituent elements. It's like reversing the process of a battery. In a battery, chemical energy becomes electrical, but here, with electrolysis, we use electrical energy to force chemicals to do something they normally wouldn't: to break apart.

During electrolysis, two electrodes, called the anode and cathode, are immersed in a substance that can conduct electricity, usually an ionic compound dissolved in water or melted down. When electricity is applied, ions in the substance migrate: positive ions head towards the negative electrode and negative ions head for the positive electrode. Once there, they gain or lose electrons in reduction and oxidation reactions, becoming neutral atoms or molecules. This is where the magic happens: elements like oxygen or chlorine gas bubble up at one electrode, while metals like copper or hydrogen gas might appear at the other.

Chemical Energy to Electrical Energy

Conversion of chemical energy to electrical energy occurs in devices like batteries. In contrast, electrolytic cells do the opposite: they take in electrical energy to drive a chemical change. But understanding the reverse process helps build context.

In a battery, a spontaneous chemical reaction happens without any external push, releasing energy. This energy is harnessed as electrons move through a circuit, creating electrical power that, for example, keeps a flashlight shining or a phone working. Electrochemical cells, like batteries, have two different metals that create an electrical difference. As the reaction progresses, one metal loses electrons (oxidation), while the other gains them (reduction), creating a flow of electrons, which is the electric current.

In the case of the electrolytic cell, however, we need an external power source, like a battery or power supply, to push the reaction in the non-natural direction - from electrical energy back to chemical.

Non-Spontaneous Chemical Reactions

Most chemical reactions we know, like a piece of metal rusting or a log burning, are spontaneous. They need no help to proceed once started. Non-spontaneous chemical reactions, on the other hand, won't go forward without some form of added energy.

In electrolysis, the electrolytic cell is the stage for these non-spontaneous reactions. With the help of an external power source, we can compel the reactions to occur. This process not only demonstrates conversion of energy but also the control we can exert over chemical processes. An easy way to remember this is to think about a door that opens only when you push a button. Without pressing the button (providing energy), the door (reaction) won't open (occur).

These non-spontaneous reactions are foundational in many industries for producing materials like aluminum or purifying water, showcasing how controlled chemistry can lead to impressive technological achievements.