Integrated SequencePhysics Chemistry Organic Biology

Web Resources

Wikipedia - Potential energy
Good clear article discussing both gravitational and electrical potential energy. Comparing and contrasting the two will help you better understand both gravitational and electrical systems.

Colegio Franklin Delano Roosevelt - Gravitational Field vs. Electric Field
Nice discussion comparing and contrasting electrostatics and gravitation. Highly recommended.



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Special points of emphasis

Work, Energy, and Power

Gravitation

One of the key concepts that can help you ensure that you understand binding energy is the concept of escape velocity in gravitational systems. An object's escape velocity is determined by the kinetic energy necessary for it to overcome gravitational binding energy.

Picture two objects, bound in a gravitational system. They have fallen together into a potential energy well. In our way of modeling it, complete separation is zero potential energy. All other values as negative.

Assume one object is the Earth and the other is a baseball. The escape velocity represents the speed the baseball would need (if there was no friction) to climb all the way out of the potential energy well it has fallen into with the Earth. How much kinetic energy would you need to add to the baseball to make the total energy (potential plus kinetic) of the ball - Earth system greater than zero?




Work, Energy, and Power

Electricity

The concept of binding energy, so useful for interpreting gravitational systems, is also crucial for interpreting systems consisting of oppositely charged particles interacting by electrostatic force. The work-energy required to separate two opposite charges represents the binding energy of the system.

This conceptual framework of binding energy is essential for understanding chemistry, although you always need to keep in mind the augmentations to the model provided by quantum mechanics. Binding energy may only find its way directly into a question or two on the MCAT, but it is one of the most important foundation stones for understanding the physical and biological sciences in general.




Work, Energy, and Power

Electricity

Atomic Theory

Applying the concepts of Dynamics and Work & Energy in Mechanics along with the a basic sense of the Electrostatic Force as we begin to understand Chemistry is one of the most important goals of the first phase of this MCAT course.

Interpreting the energy changes in an atom, for example, is fundamental to understanding chemistry. Although the atom is a quantum electrodynamical system, there is definitely a place for basic physics concepts from work & energy and classical electrodynamics to help you gain your conceptual foothold.

At a fundamental level, for example, conceptualize ionization energy as the work required to pull an electron free of an atom against electric force. . The first ionization energy is the binding energy between an atom and its highest energy ground state electron. Picture the work! Take the electrostatic potential energy from some negative value all the way to zero in your imagination.

How much work would it take to pull the electron away from the atom? This is the ionization energy.




Work, Energy, and Power

Electricity

The Chemical Bond

Continuing our basic preview of important chemistry concepts in the context of basic mechanics, let us introduce the concept of bond dissociation energy.

This is a preview of concepts you will cover in much more depth in a few weeks in Chemical Bonding. Bond dissociation energy is the binding energy of two atoms in a covalent bond, a system with negative electron density (bonding electrons) between two positively charged nuclei.

Molecular orbital theory, a quantum theory, accounts for the array of possible states for the system. However, it is still very helpful to use the concepts of classical physics in work & energy and classical electrodynamics to help conceptualize the potential energy of the system. The electrons within the internuclear space, the bonding electrons, exert electric force, holding the nuclei of the bonded atoms within the chemical bond.

To understand the energy description of the covalent bond, it can be helpful to picture bond formation, the reverse of bond dissociation. Picture two unbonded atoms coming together to form a bond. As the two atoms near one another, electron density migrates into the internuclear distance (the space between the atoms), drawing the nuclei inwards. Picture the bonding electrons, a negative charge density, pulling the atoms together, as they fall into a potential energy well.

Quantum molecular orbital dynamics makes it possible (classical physics cannot explain how the electrons localize in the internuclear space), but classical electrodynamics can help you understand the binding energy of the system. You would have to put energy into the system to pull the atoms apart. You would have to input the bond dissociation energy. We will return to this concept again and again throughout this MCAT course.




Work, Energy, and Power

Electricity

Intermolecular Forces

The States of Matter

Binding energy determined by electrodynamics also exists at the molecular level. For example, the internal energy difference between the liquid and gas phases represents electrostatic binding energy along the lines of intermolecular force.







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