Chemical Thermodynamics

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A system is the part of the universe under study (e.g., reactants in a beaker). The surroundings include everything else that can exchange energy or matter with the system (e.g., beaker, air, room).

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An isolated system exchanges neither matter nor energy with its surroundings. Example: Hot tea in a perfectly insulated thermos flask.

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A closed system can exchange energy but not matter with the surroundings. Example: Hot milk in a stoppered stainless steel flask.

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An open system can exchange both matter and energy with the surroundings. Example: Human body, which exchanges food, gases, and heat.

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State functions depend only on the initial and final states of a system, not on the path taken. Examples: Pressure (P), Temperature (T), Volume (V), Internal Energy (U), Enthalpy (H).

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Extensive properties depend on the amount of substance (e.g., mass, volume, internal energy). Intensive properties do not depend on amount (e.g., temperature, pressure, density).

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An isothermal process is one in which the temperature of the system remains constant throughout. It is achieved by heat exchange with a reservoir. Example: Melting of ice at 273 K.

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An adiabatic process is one in which no heat is exchanged between the system and surroundings. The system is thermally insulated. Example: Reaction in a thermos flask.