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Ch.5 - Thermochemistry
Chapter 5, Problem 28a

Consider a system consisting of two oppositely charged spheres hanging by strings and separated by a distance r1, as shown in the accompanying illustration. Suppose they are separated to a larger distance r2, by moving them apart. (a) What change, if any, has occurred in the potential energy of the system?

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Key Concepts

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

Electric Potential Energy

Electric potential energy is the energy stored in a system of charged particles due to their positions relative to each other. For two point charges, this energy is given by the formula U = k * (q1 * q2) / r, where k is Coulomb's constant, q1 and q2 are the magnitudes of the charges, and r is the distance between them. As the distance increases, the potential energy decreases for opposite charges, indicating that work is done against the electric force.
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Coulomb's Law

Coulomb's Law describes the force between two charged objects, stating that the force is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them. This law helps to understand how the force changes as the distance between the charges changes, which in turn affects the potential energy of the system.
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Work and Energy Transfer

In physics, work is defined as the energy transferred when a force is applied over a distance. When the charged spheres are moved apart, work is done against the electric force, resulting in a change in potential energy. This concept is crucial for understanding how energy is conserved and transformed in electrostatic systems, particularly when charges are separated or brought closer together.
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Related Practice
Textbook Question

For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic: (a) A balloon is cooled by removing 0.655 kJ of heat. It shrinks on cooling, and the atmosphere does 382 J of work on the balloon.

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Textbook Question

A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:

Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move. (a) In which case does the gas have the higher temperature after addition of the electrical energy?

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Textbook Question

A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:

Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move. (b) Identify the sign (positive, negative, or zero) of q and w in each case?

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Textbook Question

(c) Is the volume of a system a state function? Why or why not?

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Textbook Question
During a deep breath, our lungs expand about 2.0 L against an external pressure of 101.3 kPa. How much work is involved in this process (in J)?
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Textbook Question
How much work (in J) is involved in a chemical reaction if the volume decreases from 33.6 L to 11.2 L against a constant pressure of 90.5 kPa?
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