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Ch.6 - Thermochemistry
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Non è quello che usi tu?Cambia libro di testo
Capitolo 6, Problema 41

A system releases 622 kJ of heat and does 105 kJ of work on the surroundings. What is the change in internal energy of the system?

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Identify the given values: heat released by the system (q) is -622 kJ (negative because it is released), and work done by the system on the surroundings (w) is -105 kJ (negative because work is done by the system).
Recall the first law of thermodynamics, which states that the change in internal energy of a system (\(\Delta U\)) is equal to the heat added to the system plus the work done on the system: \(\Delta U = q + w\).
Substitute the given values into the first law equation: \(\Delta U = -622 \text{ kJ} + (-105 \text{ kJ})\).
Calculate the sum of the heat and work values to find the change in internal energy.
Interpret the sign of your result to determine whether the internal energy of the system increased or decreased.

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First Law of Thermodynamics

The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed. It establishes the relationship between the internal energy of a system, heat exchanged, and work done. Mathematically, it is expressed as ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.
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First Law of Thermodynamics

Internal Energy

Internal energy is the total energy contained within a system, encompassing both kinetic and potential energy at the molecular level. It reflects the energy associated with the temperature, phase, and composition of the system. Changes in internal energy occur due to heat transfer and work interactions with the surroundings.
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Internal Energy

Sign Convention in Thermodynamics

In thermodynamics, a sign convention is crucial for correctly interpreting energy changes. Heat added to the system is considered positive, while heat released is negative. Similarly, work done by the system on the surroundings is negative, while work done on the system is positive. This convention helps in accurately applying the First Law of Thermodynamics.
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