Answer to Ch 3 Critical Thinking Question

The term stability describes the tendency to change. If you are comparing two systems, the system that is more likely to change is less stable, and the system that is less likely to change is more stable.

For example, if you flip a coin in the air, it is more likely to change after it stops at the peak of its flight than when it is lying on the ground, so we say it is less stable at the peak of its flight. When things change they can do work (which is what is done when something is moved against a resistance).

The coin as it falls to the ground can bump into something else and move it, so the coin at the peak of its flight has a greater potential to do work than a coin on the ground. Energy is the capacity to do work, so the less stable coin in the air has a greater energy than a coin on the ground.

When the coin stops at the peak of its flight, it does not have a greater kinetic energy (which is the energy of motion) than a coin on the ground. We say it has greater potential energy.In summary, less stable systems have greater potential energy.

For our example, system (2) (an alpha particle and two separate electrons) is less stable than system (1) (an uncharged helium atom), so it has greater potential energy.

System (2) is more likely to change because the two negative electrons are attracted to the positive helium nucleus.

As the electrons and nucleus are drawn toward each other, they could bump into something and move it against a resistance, thus doing work, so system (2) has a greater capacity to do work and a greater energy.

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