Question

Which of the following is NOT a state function? a. Internal energy b. Heat c. Temperature d. Entropy

Short answer

Heat is NOT a state function.

Step-by-step solution

- Define State Function

A state function is a property of a system that depends only on its current state, not on the path taken to reach that state. Examples of state functions include internal energy, temperature, and entropy.

- Identify Each Option

Evaluate each given option to determine whether it is a state function. - Internal energy (a): It depends only on the state of the system.- Heat (b): It depends on the path taken to transfer energy.- Temperature (c): It depends only on the state of the system.- Entropy (d): It depends only on the state of the system.

- Identify Non-State Function

Among the options, heat is the one that depends on the path taken to transfer energy. Thus, it is not a state function.

Key concepts

Thermodynamics

Thermodynamics is the branch of physics that deals with heat, work, and the forms of energy involved in chemical or physical processes. It focuses on how energy is converted from one form to another and how it affects matter.

Thermodynamics is crucial for understanding the behavior of physical systems, both big and small. Key concepts in thermodynamics include:

• Systems and surroundings: A system is the part of the universe we are focusing on, and the surroundings are everything else.
• State variables: Properties that define the state of a system, such as temperature, pressure, and volume.
• Processes: Changes that a system undergoes, which can be isothermal, adiabatic, isobaric, or isochoric.

Understanding these principles helps predict how systems behave under different conditions and is essential for various applications in science and engineering.

Internal Energy

Internal energy is the total energy contained within a system. It includes all forms of kinetic and potential energy of the particles in the system. Importantly, internal energy is a state function.

A state function depends only on the current state of the system, not on how it got there. This means no matter the process a system undergoes, its internal energy is only determined by its present condition (e.g., temperature, volume, and pressure).

Internal energy can change through two main ways:

• Heat (q): Energy transferred due to a temperature difference between the system and surroundings.
• Work (w): Energy transferred when an external force moves an object within the system.

This relationship is captured in the First Law of Thermodynamics, which states:

\( \Delta U = q + w \)

Where \( \Delta U \) is the change in internal energy.

Heat

Heat is a form of energy transfer between systems or objects with different temperatures. It flows from the hotter object to the cooler one until thermal equilibrium is reached. Unlike internal energy, heat is not a state function.

This means that the amount of heat transferred depends on the path taken, not just the initial and final states. For instance, heating a gas can be done by changing its temperature at constant volume or constant pressure, each way requiring different amounts of heat.

Heat transfer occurs in three ways:

• Conduction: Transfer of heat through a solid material.
• Convection: Transfer of heat through fluids (liquids or gases) due to the fluid movement.
• Radiation: Transfer of heat through electromagnetic waves, without needing a medium.

Understanding heat is vital for various practical applications, such as cooking, engine design, and climate control.