Electrolytic cell is used to convert — Electrochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Define an Electrolytic Cell An electrochemical system is categorized into two main types of cells based on the direction of energy conversion: galvanic (voltaic) cells and electrolytic cells. An **electrolytic cell** is defined as an electrochemical device that utilizes external electrical energy to drive a non-spontaneous chemical reaction ($\Delta G > 0$, $E^\circ_{\text{cell}} < 0$). In this system, the reaction is forced to proceed in the thermodynamically unfavorable direction by applying an external voltage greater than the opposing cell potential. Step 2 - Analyze the Energy Conversion in the Cell The thermodynamic process occurring in an electrolytic cell can be described as follows: 1. **Input:** Electrical energy is supplied to the system via an external direct current (DC) power source (such as a battery). 2. **Process:** Electrons are forced to enter through the cathode (where reduction occurs) and leave through the anode (where oxidation occurs), driving a redox reaction at the electrode-electrolyte interfaces. 3. **Output:** The electrical energy consumed is stored in the form of chemical potential energy within the newly formed chemical products (e.g., elemental metals, gases). Thus, the overall energy transformation in an electrolytic cell is: $$\text{Electrical Energy} \longrightarrow \text{Chemical Energy}$$ A classic example is the electrolysis of molten sodium chloride ($\ce{NaCl}$): $$\text{At Anode (Oxidation):} \quad \ce{2Cl^-(l) -> Cl2(g) + 2e^-}$$ $$\text{At Cathode (Reduction):} \quad \ce{2Na^+(l) + 2e^- -> 2Na(l)}$$ $$\text{Overall Reaction:} \quad \ce{2Na^+(l) + 2Cl^-(l) -> 2Na(l) + Cl2(g)}$$ Here, electrical work is performed on the system to convert stable chloride and sodium ions into high-energy elemental sodium metal and chlorine gas. Step 3 - Evaluate the Options * **Option (A) is incorrect:** The conversion of chemical energy to electrical energy is performed by a **galvanic (voltaic) cell**, which runs spontaneously ($\Delta G < 0$) to generate an electric current (e.g., a dry cell, fuel cell, or discharging lead storage battery). * **Option (B) is correct:** As established, an electrolytic cell utilizes external electrical energy to drive non-spontaneous redox reactions, thereby converting electrical energy into chemical energy. * **Option (C) is incorrect:** The conversion of chemical energy to mechanical energy is performed by biological engines (like muscles utilizing ATP) or internal combustion engines, not electrochemical cells. * **Option (D) is incorrect:** The conversion of electrical energy to mechanical energy is performed by an **electric motor**, which is a physical device rather than an electrochemical system. $$\text{Correct Option: } \boxed{\text{B}}$$