Question

In the equilibrium: \(\mathrm{C}\) (s, diamond) \(\rightleftharpoons \mathrm{C}\) (s, graphite) \(+\) Heat (density of diamond and graphite are \(3.5\) and \(2.3 \mathrm{~g} / \mathrm{cm}^{3}\) respec tively), the equilibrium will be shifted to the left at (a) High temperature and low pressure (b) Low temperature and very high pressure (c) Low temperature and low pressure (d) High temperature and very high pressure

Short answer

(d) High temperature and very high pressure

Step-by-step solution

Understanding Reaction Direction

The given equilibrium is between diamond and graphite with an exothermic direction to the right (forming graphite releases heat). According to Le Chatelier's principle, the system will adjust to counteract changes in temperature or pressure.

Effect of Temperature on Equilibrium

When the temperature is increased, the reaction will shift towards the endothermic side to absorb the excess heat. In this case, it means shifting towards diamond formation (left side), since forming graphite (right side) is exothermic.

Effect of Pressure on Solid-Solid Equilibrium

In this equilibrium, pressure can influence which form of carbon is favored by considering density. Diamond has a higher density (3.5 g/cm³) compared to graphite (2.3 g/cm³). Increasing pressure would favor the formation of the denser phase, which is diamond (left side).

Evaluating Given Options

Based on the analysis, high temperature will favor the left side since this is the endothermic side, and very high pressure will also favor the left side since diamond is denser. Thus, the correct option that will shift the equilibrium to the left is 'High temperature and very high pressure'.

Key concepts

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept in chemical equilibrium. It states that if a dynamic equilibrium is disturbed by changing the conditions—such as concentration, temperature, or pressure—the system responds by adjusting itself to counteract the effect of the change. This means that equilibrium shifts to minimize the imposed change.
For instance, if you increase the temperature of a system in equilibrium, according to Le Chatelier, the system will attempt to absorb this excess heat. This shift usually involves moving towards the endothermic reaction.

• If pressure is increased, the system will shift towards the side with fewer gas particles, if gases are involved.
• If the concentration of a component is increased, the equilibrium will shift in the direction that reduces the concentration of that component.

The principle helps predict the direction of shift for exothermic and endothermic reactions, as well as the effects of changing conditions on equilibrium.

Exothermic and Endothermic Reactions

Exothermic and endothermic reactions describe how heat is absorbed or released in chemical reactions. An exothermic reaction releases heat, meaning it transfers energy to the surroundings. This kind of reaction often feels hot or causes a temperature increase in the surrounding area.
On the other hand, an endothermic reaction absorbs heat from its surroundings. In an exothermic reaction, forming graphite from diamond releases heat, making it exothermic. Hence, increasing temperature will shift the equilibrium to the left (towards diamond) to absorb heat (endothermic process).

• Exothermic Reaction: Heat is a product; released energy can sometimes make the reaction feel hotter.
• Endothermic Reaction: Heat is a reactant; these reactions require continuous energy input to proceed.

Understanding these reactions is crucial when predicting how equilibrium shifts with temperature changes.

Effect of Pressure on Equilibrium

Pressure changes affect chemical equilibria, particularly in reactions involving gases. However, Le Chatelier's principle can also be applied to solid-solid equilibria by considering the densities.
Usually, increasing pressure will favor the formation of the phase that occupies less volume. In the given equilibrium, diamond represents the denser phase. Therefore, increasing pressure will shift the equilibrium towards the diamond formation.
This concept mostly applies to gaseous reactions, but understanding the effect of pressure on solid-solid equilibria also requires considering physical properties like density.

• An increase in pressure favors the denser phase in solid-solid reactions.
• In gaseous reactions, pressure shifts equilibrium towards the side with fewer moles of gas.

Thus, recognizing how pressure influences different types of reactions is pivotal in mastering chemical equilibria.

Solid-Solid Equilibrium

In a solid-solid equilibrium, the substances involved are in different solid phases, as seen with diamond and graphite in carbon.
This type of equilibrium can be influenced by both temperature and pressure, similar to equilibria involving gases and liquids. However, since the substances are both in the solid phase, pressure effects depend on density differences. Diamond, for instance, has a higher density than graphite.
Temperature plays a significant role too, driving the reaction towards the endothermic or exothermic reaction based on energy changes, as explained by Le Chatelier's Principle.

• Solids in equilibrium can still respond to changes in pressure and temperature, albeit differently than gases.
• Density differences between solid phases guide how pressure affects these equilibria.

Understanding solid-solid equilibria is important for comprehending how different forms of a substance can coexist under varying conditions.