Ch.7 - Thermochemistry

Problem 39

Chapter 7, Problem 39

Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a negative ΔE_sys? a. The internal energy of the system increases and the internal energy of the surroundings decreases. b. The internal energy of both the system and the surroundings increases. c. The internal energy of both the system and the surroundings decreases. d. The internal energy of the system decreases and the internal energy of the surroundings increases.

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Understand that \( \Delta E_{sys} \) represents the change in internal energy of the system.

A negative \( \Delta E_{sys} \) indicates that the system is losing energy.

According to the law of conservation of energy, energy lost by the system is gained by the surroundings.

Therefore, if the system's internal energy decreases, the surroundings' internal energy must increase.

Identify the statement that matches this description: 'The internal energy of the system decreases and the internal energy of the surroundings increases.'

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Internal Energy

Internal energy is the total energy contained within a system, encompassing kinetic and potential energies of the particles. It is a state function, meaning it depends only on the current state of the system, not on how it reached that state. Changes in internal energy (ΔE) occur due to heat transfer or work done on or by the system.

First Law of Thermodynamics

The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. In the context of a system and its surroundings, this law implies that any change in the internal energy of a system is equal to the heat added to the system minus the work done by the system on its surroundings (ΔEsys = q - w).

Negative ΔEsys

A negative change in internal energy (ΔEsys < 0) indicates that the system has lost energy, typically through heat transfer to the surroundings or work done by the system. This means that the internal energy of the system decreases while the surroundings gain energy, leading to an increase in their internal energy. Understanding this concept is crucial for analyzing energy exchanges in thermodynamic processes.

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