Problem 68 - Chemistry The Molecular Nature of Matter

Question

Use Le Châtelier's principle to predict the effect of adding heat in the equilibrium: solid \(+\) heat \(\rightleftharpoons\) liquid.

Step-by-Step Solution

Answer

Adding heat to the equilibrium shifts the reaction to the right, increasing the formation of liquid.

Step 1: Understand Le Châtelier's Principle

Le Châtelier's Principle states that if an external stress is applied to a system at equilibrium, the system adjusts in such a way as to partially counteract the imposed change and a new equilibrium is established.

Step 2: Identify the Direction of the Reaction with Added Heat

In the given equilibrium, heat is a reactant. According to Le Châtelier's Principle, adding more of a reactant shifts the equilibrium to the right, favoring the formation of products. Hence, adding heat will drive the reaction towards the formation of liquid.

Step 3: Predict the Effect of Heat Addition

By adding heat to the system, the equilibrium will shift to the right, more solid will melt to form liquid to absorb the extra heat added, until a new equilibrium position is reached.

Key Concepts

Chemical Equilibrium

Chemical equilibrium is a fundamental concept in chemistry that occurs when the rate of the forward reaction equals the rate of the reverse reaction, resulting in no observable change in the amounts of reactants and products. This state of balance doesn't mean that the reactants and products have equal concentrations, but rather that their concentrations have stabilized at a certain ratio and will remain constant over time unless disturbed by external factors.

Understanding chemical equilibrium is essential for predicting how a system behaves when conditions are changed. Le Châtelier's Principle provides a qualitative tool for predicting the shift in equilibrium in response to such changes. It’s important to note that reaching equilibrium is a dynamic process — reactions continue to occur, but with no net change after equilibrium is established.

Heat Effect on Equilibrium

The impact of heat on a system at equilibrium is a prime example of how external conditions can influence chemical reactions. According to Le Châtelier's Principle, if heat is added to a system, the equilibrium will shift to favor the reaction that absorbs heat, thus reducing the impact of the temperature increase. This often involves endothermic reactions, which require heat, leading to an increased production of the reaction's products.

Conversely, if heat is removed from the system, it favors exothermic reactions, which release heat, thus mitigating the cooling effect by forming more reactants. Being aware of these shifts is important for controlling reactions in industrial processes and understanding natural phenomena. It also highlights the fundamental connection between chemical reactions and thermodynamics.

Phase Transition

A phase transition is the transformation of a substance from one state of matter — solid, liquid, or gas — to another. Equilibrium plays a vital role during a phase transition, such as when a solid melts into a liquid. This process is both temperature and pressure dependent, and at equilibrium, the two phases coexist, exchanging particles but maintaining a stable ratio.

In the context of Le Châtelier's Principle, adding heat to a solid-liquid equilibrium will shift the equilibrium towards the liquid phase, promoting melting, as the system seeks to counteract the added heat by absorbing it during the phase transition. This insight is crucial not only in scientific applications but also in everyday phenomena, such as the melting of ice or the boiling of water.