Imagine a reaction that results in a change in both volume and temperature: (a) Has any work been done? If so, is its sign positive or negative?
Ch.9 - Thermochemistry: Chemical Energy
Chapter 9, Problem 36b
Redraw the following diagram to represent the situation (b) when work has been lost by the system.
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Step 1: Identify the initial state of the system. The diagram shows a cylinder with a piston applying pressure (P) downwards on a liquid surface.
Step 2: Understand the concept of work done by the system. When work is done by the system, it typically involves the system expanding against an external pressure.
Step 3: Consider the scenario where work has been lost by the system. This implies that the system has done work on the surroundings, causing the piston to move upwards.
Step 4: Redraw the diagram to reflect the new situation. The piston should be at a higher position than initially, indicating that the system has expanded.
Step 5: Ensure the pressure (P) is still acting downwards on the piston, but the volume of the liquid has increased, showing that work has been done by the system.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Work in Thermodynamics
In thermodynamics, work is defined as the energy transfer that occurs when a force is applied over a distance. When a system does work on its surroundings, it loses energy, which can affect its internal energy and temperature. Understanding how work is done by or on a system is crucial for analyzing energy changes in processes such as expansion or compression.
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Pressure and Force
Pressure is defined as the force exerted per unit area on a surface. In the context of the diagram, the pressure (P) acting downwards on the liquid surface indicates the force applied by the gas or liquid above it. This concept is essential for understanding how pressure influences the behavior of fluids and the work done by the system.
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System and Surroundings
In thermodynamics, a system refers to the part of the universe being studied, while the surroundings are everything outside the system. When analyzing work done by a system, it is important to distinguish between energy changes within the system and those in the surroundings. This distinction helps in understanding how energy is transferred and conserved during processes.
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Related Practice
Textbook Question
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Textbook Question
Imagine a reaction that results in a change in both volume and temperature:
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Textbook Question
Redraw the following diagram to represent the situation (a) when work has been gained by the system and
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Textbook Question
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Textbook Question
The reaction of A with B to give D proceeds in two steps: (1) A + B → C ΔH° = -20 kJ (2) C + B → D ΔH° = +50 kJ (3) A + 2B → D ΔH° = ? (a) Which Hess's law diagram represents the reaction steps and the overall reaction? Diagram 1 Diagram 2
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Textbook Question
The reaction of A with B to give D proceeds in two steps: (1) A + B → C ΔH° = -20 kJ (2) C + B → D ΔH° = +50 kJ (3) A + 2B → D ΔH° = ? (b) What is the value of ΔH° for the overall reaction A + 2 B → D ΔH° = ?
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