Textbook Question
The diagram shows four states of a system, each with different internal energy, E. (a) Which of the states of the system has the greatest internal energy?
Ch.5 - Thermochemistry
Chapter 5, Problem 7
You may have noticed that when you compress the air in a bicycle pump, the body of the pump gets warmer. (c) Based on your answers to parts (a) and (b), can you determine the sign of _x001F_E for compressing the air in the pump? If not, what would you expect for the sign of _x001F_E? What is your reasoning?
Verified step by step guidance1
Step 1: Understand the context of the problem. When you compress air in a bicycle pump, you are doing work on the gas. This is a thermodynamic process where the system (air) is being compressed, and energy is transferred to it.
Step 2: Recall the First Law of Thermodynamics, which states that the change in internal energy (ΔE) of a system is equal to the heat added to the system (q) plus the work done on the system (w): ΔE = q + w.
Step 3: Consider the work done on the system. In this case, work is done on the air by compressing it, which means w is positive. This is because work is being done on the system, increasing its internal energy.
Step 4: Analyze the heat exchange. Since the pump gets warmer, it suggests that the process is adiabatic or nearly adiabatic, meaning there is little to no heat exchange with the surroundings (q ≈ 0).
Step 5: Determine the sign of ΔE. With q ≈ 0 and w being positive, the change in internal energy ΔE = q + w will be positive, indicating an increase in the internal energy of the air in the pump.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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 compressing air in a bicycle pump, the work done on the gas increases its internal energy, which can lead to a rise in temperature, illustrating the conversion of mechanical work into thermal energy.
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01:18
First Law of Thermodynamics
Work and Heat Transfer
In thermodynamics, work refers to the energy transferred when a force is applied over a distance, while heat transfer involves the movement of thermal energy due to a temperature difference. When compressing air, work is done on the gas, resulting in an increase in internal energy, which manifests as an increase in temperature, indicating that heat is not lost but rather generated.
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02:19Heat Capacity
Internal Energy
Internal energy is the total energy contained within a system, including kinetic and potential energy at the molecular level. When air is compressed in the pump, the molecules are forced closer together, increasing their kinetic energy and thus raising the internal energy of the air, which is reflected in the observed temperature increase.
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Related Practice
Textbook Question
The diagram shows four states of a system, each with different internal energy, E. (c) Write an expression for the difference in energy between State C and State D.
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Textbook Question
Imagine a container placed in a tub of water, as depicted in the accompanying diagram. (a) If the contents of the container are the system and heat is able to flow through the container walls, what qualitative changes will occur in the temperatures of the system and in its surroundings? From the system's perspective, is the process exothermic or endothermic?
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Textbook Question
In the accompanying cylinder diagram, a chemical process occurs at constant temperature and pressure. (a) Is the sign of w indicated by this change positive or negative?
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Textbook Question
(b) Why does increasing the temperature cause a solid substance to change in succession from a solid to a liquid to a gas?
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