Concepts of System and Surroundings — Revision Notes

⚡ 30-Second Revision

System — Part of universe under study.
Surroundings — Everything outside the system.
Boundary — Separates system from surroundings.
Open System — Exchanges matter AND energy (e.g., open beaker, living organism).
Closed System — Exchanges energy but NOT matter (e.g., sealed container, gas in cylinder).
Isolated System — Exchanges NEITHER matter NOR energy (e.g., ideal thermos, Universe).
Diathermic Boundary — Allows heat exchange.
Adiabatic Boundary — Prevents heat exchange.
First Law for Isolated System — $\Delta U = 0$ (since $q=0, w=0$).

2-Minute Revision

The foundation of thermodynamics rests on defining the system (what we study) and the surroundings (everything else). The boundary is the interface between them. Systems are classified based on their interaction with the surroundings:

1
Open System — Exchanges both matter and energy. Think of an open pot of boiling water, where steam (matter) escapes and heat (energy) dissipates. Living organisms are prime examples.
2
Closed System — Exchanges energy but not matter. A sealed reaction vessel or a gas in a cylinder with a piston are examples. Heat can be added or removed, and work can be done, but no mass enters or leaves.
3
Isolated System — Exchanges neither matter nor energy. A perfectly insulated thermos flask is an approximation. The entire universe is considered an isolated system. For an isolated system, the internal energy ($Delta U$) remains constant because both heat ($q$) and work ($w$) are zero.

Boundaries can be diathermic (allow heat) or adiabatic (prevent heat), and permeable (allow matter) or impermeable (prevent matter). Understanding these distinctions is crucial for applying thermodynamic laws correctly.

5-Minute Revision

To master thermodynamics, begin with a clear understanding of system, surroundings, and boundary. The system is your chosen focus area, the surroundings are everything outside it, and the boundary is the separator. This boundary can be real or imaginary, rigid or flexible, and crucially, it dictates the exchange of matter and energy.

There are three primary types of systems:

1
Open System — This system is fully interactive. It allows both matter (e.g., mass, molecules) and energy (e.g., heat, work) to cross its boundary. For example, an open beaker of acid reacting with a metal: hydrogen gas (matter) escapes, and heat (energy) is released to the air. Living organisms are classic open systems.
2
Closed System — This system is partially interactive. It permits the exchange of energy (heat or work) but strictly prevents the exchange of matter. Imagine a sealed glass bottle of hot tea. The tea will cool down (exchanging heat), but no tea (matter) can escape. A gas in a cylinder with a movable, sealed piston is another example; the gas can be compressed (work done) or heated, but its mass remains constant.
3
Isolated System — This is an ideal, non-interactive system. It allows neither matter nor energy to cross its boundary. A perfectly insulated thermos flask containing hot coffee approximates an isolated system for a limited time. The universe itself is considered the ultimate isolated system. A key implication for an isolated system is that its internal energy ($Delta U$) remains constant, as both heat ($q$) and work ($w$) exchanged are zero ($Delta U = q + w = 0$).

Boundaries also have properties: a diathermic boundary allows heat flow (like a metal wall), while an adiabatic boundary prevents it (like a perfectly insulated wall). Similarly, boundaries can be permeable (allow matter) or impermeable (prevent matter). Correctly identifying the system type based on a given scenario is the first and most critical step in solving any thermodynamic problem in NEET.

Prelims Revision Notes

Concepts of System and Surroundings (CHE-06-01) - NEET Revision Notes

1. System: The specific part of the universe chosen for thermodynamic study. Its properties are observed.

2. Surroundings: Everything external to the system that can interact with it.

3. Boundary: The real or imaginary surface separating the system from its surroundings. It defines the limits of interaction. * Diathermic Boundary: Allows heat exchange (e.g., metal container).

* Adiabatic Boundary: Prevents heat exchange (e.g., insulated container). * Permeable Boundary: Allows matter exchange. * Impermeable Boundary: Prevents matter exchange. * Rigid Boundary: Fixed volume, no P-V work.

* Flexible Boundary: Volume can change, P-V work possible.

4. Types of Systems (based on matter and energy exchange):

* Open System: * Exchanges both matter and energy with surroundings. * Examples: Open beaker of boiling water, living organisms, rocket engines. * Matter and energy content can change. * Closed System: * Exchanges energy (heat/work) but NOT matter with surroundings.

* Examples: Sealed reaction vessel, gas in a cylinder with a piston, pressure cooker. * Mass of system is constant; energy content can change. * Isolated System: * Exchanges NEITHER matter NOR energy with surroundings.

* Examples: Perfectly insulated thermos flask (approximation), the Universe. * Mass and total energy of system are constant. * First Law Implication: For an isolated system, $q=0$ and $w=0$, therefore $\Delta U = 0$.

5. Key Distinctions for NEET:

* 'Sealed' implies no matter exchange (closed or isolated). * 'Insulated' implies no heat exchange (adiabatic boundary, characteristic of isolated systems). * 'Rigid' implies no volume change, so no P-V work ($w=0$ if only P-V work is considered).

6. Thermodynamic Equilibrium: A state where macroscopic properties (T, P, V, composition) are constant over time, indicating thermal, mechanical, and chemical balance.

7. Importance for NEET: This topic is foundational. Correctly identifying the system type is crucial for applying the First Law of Thermodynamics and understanding subsequent concepts like enthalpy, internal energy, and entropy changes. Expect conceptual questions and scenario-based identification.

Vyyuha Quick Recall

Open Can Interact: Open: Exchanges Matter & Energy (ME) Closed: Exchanges Energy, no Matter (E, no M) Isolated: Exchanges Neither Matter nor Energy (No ME)