Question

The critical temperature of a substance is: (a) The temperature above which the substance undergoes decomposition (b) The temperature above which a substance can exist only in gaseous state (c) Boiling point of the substance (d) All are wrong

Short answer

The correct answer is (b) The temperature above which a substance can exist only in gaseous state.

Step-by-step solution

Understanding Critical Temperature

Critical temperature of a substance is defined as the temperature above which the substance cannot exist in liquid form regardless of the pressure applied.

Analyzing Options

(a) refers to decomposition, which is unrelated to the critical temperature. (c) refers to the boiling point, which is not the same as critical temperature but is a specific temperature at a given pressure where liquid and gas phases exist in equilibrium. Thus both (a) and (c) are incorrect.

Identifying the Correct Option

Option (b) most accurately describes the critical temperature, as it is the temperature above which a substance cannot be liquefied and can only exist in the gaseous state, regardless of pressure.

Eliminating Incorrect Options

Option (d) is not applicable as there is at least one correct option (b).

Key concepts

Physical Chemistry

Physical chemistry delves into the principles and theories that explain the physical properties and changes of matter. Fundamental to this branch of chemistry is the study of the critical temperature, which is a pivotal concept in understanding how substances behave under different temperatures and pressures.

Physical chemistry combines the principles of physics and chemistry to analyze the dynamic changes that matter undergoes. This includes a deep dive into thermodynamics, which is particularly relevant when discussing the critical temperature. Thermodynamics allow us to comprehend phase changes and predict the conditions under which a substance will transition from one state of matter to another. The critical temperature, from a physical chemistry standpoint, is crucial for grasping the limits of these transitions.

States of Matter

The concept of states of matter is foundational in understanding critical temperature. Generally, matter exists in one of three states: solid, liquid, or gas. Each state has distinctive characteristics and the transitions between these states can occur due to changes in environmental conditions like temperature and pressure.

For example, when a liquid reaches its boiling point at a certain pressure, it will begin to turn into a gas—a process we are familiar with when boiling water. However, the critical temperature of a substance represents a unique point beyond which the distinction between the liquid and gas phases ceases to exist, regardless of pressure. Above this temperature, a substance can only exist in a supercritical fluid state, which shares properties of both gases and liquids but is distinctly different from either traditional state.

Phase Transition

A phase transition refers to the transformation of a substance from one state of matter to another. Common phase transitions include melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas), and condensation (gas to liquid).

Each phase transition point is tightly associated with a specific temperature and pressure. The critical temperature, in the context of phase transitions, is the temperature at which a substance transitions from a liquid to a gaseous state and cannot be reverted back to liquid, no matter how much pressure is applied. Understanding this allows us to not just follow step-by-step solutions but also to predict material behavior, design industrial processes, and develop new technologies that manipulate different phases of substances for practical applications.