Question

What is a nonspontancous process? Give an example.

Short answer

A nonspontaneous process is one that requires energy input to occur, such as the electrolysis of water where electricity is used to decompose water into hydrogen and oxygen.

Step-by-step solution

Definition of Nonspontaneous Process

Understand that a nonspontaneous process is one that does not occur naturally without input of energy from an external source. This is in contrast to a spontaneous process, which can take place on its own under a given set of conditions.

Identification of Nonspontaneous Process Example

Consider an example such as the electrolysis of water. In this process, electrical energy is used to cause water to decompose into hydrogen and oxygen gases. This requires continuous input of energy and will not occur under standard conditions without it.

Explanation of Nonspontaneity in the Example

Explain that the electrolysis of water is nonspontaneous because it requires an electric current to occur. Without this energy input, the reaction would not proceed because the products (hydrogen and oxygen gases) have higher energy than the reactants (water), making the reaction energetically unfavorable without external energy.

Key concepts

Chemical Thermodynamics

Chemical thermodynamics is a branch of thermodynamics that applies its principles to chemical reactions and processes. It helps us understand how energy is transformed in these reactions and dictates whether a process will occur spontaneously. The two main laws of thermodynamics at play in chemical reactions are the first law, which states that energy cannot be created or destroyed, and the second law, which indicates that the total entropy of an isolated system can never decrease over time.

A key concept in chemical thermodynamics is Gibbs free energy (\( G \)), which combines enthalpy (\( H \)), temperature (\( T \)), and entropy (\( S \)) to predict the spontaneity of a process: \[ G = H - T\times S \.\] A negative Gibbs free energy indicates a spontaneous reaction, while a positive value suggests the reaction is nonspontaneous and requires external energy input to proceed.

Electrolysis of Water

The electrolysis of water is a classic example of a nonspontaneous process that can be understood through chemical thermodynamics. To separate water into hydrogen and oxygen gas, we need to introduce electricity. This process involves passing an electric current through water, usually with some soluble electrolyte to improve conductivity, which then decomposes the water molecules.

During electrolysis, the water at the cathode is reduced to hydrogen gas, while at the anode, water is oxidized to oxygen gas. The reaction equations are as follows:

• At the cathode: \( 2H_2O(l) + 2e^- \rightarrow H_2(g) + 2OH^-(aq) \)
• At the anode: \( 2H_2O(l) \rightarrow O_2(g) + 4H^+(aq) + 4e^- \)

These reactions are not favorable under standard conditions without the addition of electricity, thus making it a perfect illustration of a nonspontaneous process.

Energy Input in Reactions

Understanding energy input in reactions is crucial for manipulating and predicting the course of chemical processes. In nonspontaneous reactions such as the electrolysis of water, continuous external energy must be supplied for the reaction to take place. This energy can take many forms, including electricity, light, or heat.

The energy provided to a nonspontaneous reaction is used to overcome an inherent energy barrier – the activation energy. This is the minimum energy necessary to initiate a chemical reaction. For example, in electrolysis, electricity provides the activation energy needed to break the bonds in water molecules. The energy demands of a reaction can often be reduced by using a catalyst, which offers an alternative pathway with a lower activation energy.

Spontaneous vs Nonspontaneous Processes

Distinguishing between spontaneous and nonspontaneous processes is a fundamental aspect of chemical thermodynamics. Spontaneous processes are those that occur naturally under a given set of conditions; they are driven by a decrease in Gibbs free energy (\( \triangle G < 0 \)) and often, but not always, lead to an increase in disorder or entropy (\( \triangle S > 0 \)).

By contrast, nonspontaneous processes such as the electrolysis of water require input of energy to proceed because they are associated with an increase in Gibbs free energy (\( \triangle G > 0 \)). These processes are also characterized by a decrease in entropy within the system, essentially moving from a state of lower energy and higher disorder to one of higher energy and lower disorder. Understanding these principles helps explain why external energy must be supplied to drive certain reactions, like electrolysis.