Problem 21 - Chemistry in 30 days

Question

Adsorption is accompanied by the evolution of heat. So acconding to Le- Chatelier principle the amount of substance adsorbed should (a) increase with decrease in temperature (b) increase with increase in temperature (c) decrease with decrease in temperature (d) decrease with decrease in temperature

Step-by-Step Solution

Answer

(a) increase with decrease in temperature.

Step 1: Analyzing Le-Chatelier's Principle

Le-Chatelier's principle states that if a dynamic equilibrium is disturbed, the system will adjust to counteract the disturbance. In the context of adsorption, which is exothermic (releases heat), a decrease in temperature would be a shift away from releasing more heat.

Step 2: Relation Between Temperature and Adsorption

For exothermic processes like adsorption, lowering the temperature favors the forward reaction because the system strives to release less heat. Hence, a decrease in temperature will lead to an increase in adsorption.

Step 3: Final Conclusion

Combining the insights from the previous steps, if the temperature decreases, adsorption increases to counterbalance the change as suggested by Le-Chatelier's principle in an exothermic process.

Key Concepts

Adsorption

Adsorption is a process where molecules from a gas or liquid stick to the surface of a solid. This sticking process happens due to forces at the molecular level. Imagine tiny particles gathering on the surface of a material, forming a thin layer. This is not to be confused with absorption, where substances penetrate the bulk of the material.
A great way to picture adsorption is to think about how activated charcoal works in air purifiers. It captures unwanted molecules from the air, making the air cleaner. Adsorption is often used in filtration and purification techniques.

• It is surface-specific and depends on factors like temperature and pressure.
• Adsorption can be physical (weak forces) or chemical (strong forces) depending on interactions.

Exothermic Process

An exothermic process is one in which energy is released in the form of heat. This happens during chemical reactions or physical changes when bonds are formed that release energy.
Burning wood in a fireplace is a common exothermic reaction. As the wood burns, you feel heat radiating outwards. Similar principles apply to adsorption, which is typically exothermic.
In an exothermic reaction:

• The system releases energy to its surroundings.
• The environment becomes warmer as a result of this release.
• Reactions often occur spontaneously as they lead to a decrease in energy.

These processes are fundamental in understanding phenomena like the warmth felt in chemical hand warmers or reactions in a combustion engine.

Dynamic Equilibrium

Dynamic equilibrium occurs when the forward and reverse reactions happen at the same rate in a closed system. This does not mean the reactions stop, rather they continue, but there's no net change in the concentration of reactants and products.
In simpler terms, picture two people standing on a seesaw trying to balance. Each move they make is counteracted by the other to maintain balance. In chemistry, when a reaction reaches dynamic equilibrium, it appears as though nothing is happening, but molecular activity is continuous.

• The concentrations of substances remain constant over time.
• It requires a closed system where neither reactants nor products can escape.
• Le-Chatelier's principle can be used to predict how changes in conditions affect the equilibrium position.

Understanding dynamic equilibrium is crucial in predicting how varying conditions like temperature or pressure will influence a chemical system, making it a cornerstone in chemical kinetics and thermodynamics.