The Laws of Thermodynamics Unit 3: Bioenergetics Honors Biology Monkemeier

Energy Conversions All of the activities of living organisms involve energy changes aka energy conversions. Two universal laws govern all energy conversions (aka energy changes) in the universe. The two laws are known as the Laws of Thermodynamics.

The First Law of Thermodynamics Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed.

First Law of Thermodynamics

Energy Flow Through Living Systems Living Systems require a constant supply of energy. In living systems chemical potential energy stored in some molecules can be shifted to other molecules and stored in different chemical bonds, or it can be converted into other forms, such as kinetic energy, light, or electricity.

Heat During each energy conversion, some of the energy dissipates into the environment as HEAT, which is a measure of the random motion of molecules (and therefore a measure of one form of kinetic energy). Living organisms can not harness heat to perform work because cells are too small to create a heat differential.

Energy Flow through Living Systems Energy continuously flows through the biological world in one direction, with new energy from the SUN continuously enterring the system to replace the energy dissipated as heat.

HEAT Heat can only be harnessed to perform work when there is a heat gradient. Heat gradient = temperature difference between two areas. Cells are too small to maintain significant internal temperature differences, so heat energy is incapable of performing the work of cells. Cells MUST RELY UPON CHEMICAL ENERGY!

First Law of Thermodynamics and HEAT! Although the total amount of energy in the universe remains constant, the energy available to do work decreases as more of it progressively dissipates as heat.

Second Law of Thermodynamics The Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy.entropy

Second Law of Thermodynamics The second law is based on human experience. It doesn’t come from complicated theory and equations. So, think of these experiences that you have had: – A rock will fall if you lift it up and then let go. – Hot frying pans cool down when taken off the stove. – Iron rusts (oxidizes) in the air. – Air in a high-pressure tire shoots out from even a small hole in its side to the lower pressure atmosphere. – Ice cubes melt in a warm room.

Second Law of Thermodynamics Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so. A watch-spring-driven watch will run until the potential energy in the spring is converted, and not again until energy is reapplied to the spring to rewind it. A car that has run out of gas will not run again until you walk 10 miles to a gas station and refuel the car. Once the potential energy locked in carbohydrates is converted into kinetic energy (energy in use or motion), the organism will get no more until energy is input again. In the process of energy transfer, some energy will dissipate as heat.

Second Law of Thermodynamics = Law of Entropy Entropy is a measure of disorder: cells are NOT disordered and so have low entropy. Entropy The flow of energy maintains order and life. Entropy wins when organisms cease to take in energy and die.

2 nd Law = Law of Entropy The Second Law of Thermodynamics states that the disorder, or entropy, in the universe is increasing. This also means that conversions of energy from one form to another are inefficient, with some energy being lost to cells as HEAT. (REMINDER the word LOST means that organisms can not harness HEAT to do work.)

Second Law of Thermodynamics The Second law of Thermodynamics predicts that matter and energy tend to become increasingly disorganized in this universe. The law says that disorder is more probable than order and that to maintain order, it is necessary to expend energy. The Second law implies that there can be no such thing as a perfectly insulated container and that no transfer of energy can occur without some energy loss.

Second Law of Thermodynamics The Second Law of Thermodynamics Explains this Pyramid of Energy. Moving from producers towards carnivores there is less useful energy available because as energy transforms from one level to the next some of it is converted into HEAT which is a useless form of energy to organisms.

Second Law – Final Thoughts In general, energy transformations proceed spontaneously to convert matter from a more ordered, less stable form to a less ordered, but more stable form. The Second Law is often called “time’s arrow”. When the universe was formed it held all of the potential energy it will ever have. It has become progressively more disordered since, with every energy exchange increasing the amount of entropy (disorder)

Laws of Thermodynamics and FREE ENERGY Free energy is the energy available to do work in any system. Free energy is important to cells (organisms) and cells store and release free energy using the ATP molecule. The chemical reactions inside of cells can be explained using the Laws of Thermodynamics. The chemical reactions (inside and outside of cells) can be predicted based on free energy changes.

What’s Next? The next PPT will focus upon predicting chemical reactions and free energy changes! The words exergonic, endergonic, activation energy will all come back!