Laws of Thermodynamics: Videos & Practice Problems

The First Law of Thermodynamics states that energy can be transferred and transformed but cannot be created or destroyed, emphasizing the conservation of energy. The Second Law introduces entropy, a measure of disorder, indicating that energy transfers are never 100% efficient, leading to increased universal entropy. Living organisms can input energy to create order, but the natural tendency is towards greater disorder. Understanding these laws is crucial for grasping energy dynamics in biological systems, including processes like photosynthesis and cellular respiration.

Laws of Thermodynamics

Thermodynamics is fundamentally the study of energy and its transfers. The First Law of Thermodynamics, also known as the principle of conservation of energy, states that energy can be transferred between substances and transformed from one form to another, but it cannot be created or destroyed. This means that the total amount of energy in a closed system remains constant; the energy before a process equals the energy after the process.

For example, energy can shift between kinetic energy and potential energy. A practical illustration of this law can be seen in biological systems. In plants, chloroplasts perform photosynthesis, capturing solar energy from the sun and converting it into chemical energy stored in glucose. This process not only produces glucose but also releases oxygen as a byproduct. The energy from the sun is thus transformed into a usable form for the plant.

Similarly, animals, such as rabbits, obtain energy by consuming plants. When a rabbit eats leaves, it absorbs the chemical energy from glucose, which is then converted into adenosine triphosphate (ATP) through cellular respiration. ATP serves as a direct energy source for cellular processes. When organisms die or undergo respiration, they release carbon dioxide and water, which are essential for photosynthesis, thus continuing the cycle of energy transfer.

This cyclical flow of energy demonstrates that while energy changes forms and moves between different entities, it is never lost or created anew. The First Law of Thermodynamics emphasizes the conservation of energy, highlighting the interconnectedness of life and energy transformations in ecosystems.

Which of the following statements describes the first law of thermodynamics?
a) Energy cannot be created or destroyed.
b) Energy cannot be transferred or transformed.
c) Also called The Principle of Creation of Energy.
d) Energy can be destroyed.

• A. Energy cannot be created or destroyed.
• B. Energy cannot be transferred or transformed.
• C. Also called The Principle of Creation of Energy.
• D. Energy can be destroyed.

Answer: (A)

Entropy

Understanding entropy is crucial before delving into the second law of thermodynamics. Entropy is defined as a measure of disorder or randomness within a system. The greater the disorder, the higher the entropy. For instance, consider a pool table: when the billiard balls are neatly arranged, the system exhibits low entropy due to its high order. Conversely, when the balls are scattered across the table, the system is disordered, resulting in higher entropy.

This concept illustrates that systems naturally progress from order to disorder, reflecting the universe's tendency towards maximum entropy. In essence, reactions tend to move towards a state of greater disorder, or higher entropy. However, it is important to note that reactions can decrease the entropy of a system, but this requires an input of energy. Living organisms exemplify this principle by utilizing energy to create order within their systems, counteracting the natural trend towards disorder.

In summary, while the universe tends to evolve towards higher entropy, life has the unique ability to input energy to maintain or create order. This foundational understanding of entropy will be essential as we explore its application in the second law of thermodynamics.

Which of the following images has less entropy?

a) Image A has less entropy.
b) Image B has less entropy.

• A. Image A has less entropy.
• B. Image B has less entropy.

Answer: (A)

Second Law of Thermodynamics

The second law of thermodynamics is a fundamental principle that highlights the limitations of energy conversion processes. It asserts that achieving 100% efficiency in energy transfer is impossible due to the inevitable loss of heat energy during these processes. This loss contributes to an increase in the overall entropy of the universe, which is a measure of disorder or randomness in a system.

Heat is defined as a form of kinetic energy that transfers between two objects with differing temperatures. For instance, consider the energy flow from the sun to plants. This process illustrates that while solar energy is harnessed by plants, some energy is inevitably lost as heat, making the conversion less than fully efficient. Similarly, when an organism consumes a plant, or when a predator eats its prey, energy is transferred, but again, a portion of that energy is lost as heat. This continual loss of usable energy during transfers is a key aspect of the second law.

As energy is transformed from one form to another—whether from solar energy to chemical energy in plants, or from one organism to another—entropy increases. This means that the universe's entropy is always on the rise with each energy transfer, reinforcing the idea that energy conversions are inherently inefficient. Understanding this principle is crucial as it lays the groundwork for further exploration of thermodynamic concepts in the study of energy systems.

When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
a) It is used to power yet more cellular work in the surroundings.
b) It is captured to store energy as more heat in the system.
c) It is used to generate ADP.
d) It is lost to the environment.

• A. It is used to power yet more cellular work in the surroundings.
• B. It is captured to store energy as more heat in the system.
• C. It is used to generate ADP.
• D. It is lost to the environment.

Answer: (D)

Which of the following statements is true regarding how energy moves up the food chain?
a) All of the energy is not transferred from producer to consumer because some of the energy is destroyed.
b) All of the energy is transfer from producer to consumer.
c) All of the energy is not transferred from producer to consume because some of the energy is lost as heat.
d) None of the above.

• A. All of the energy is not transferred from producer to consumer because some of the energy is destroyed.
• B. All of the energy is transfer from producer to consumer.
• C. All of the energy is not transferred from producer to consume because some of the energy is lost as heat.
• D. None of the above.

Answer: (C)

Here’s what students ask on this topic:

What is the First Law of Thermodynamics?

The First Law of Thermodynamics, also known as the principle of conservation of energy, states that energy can be transferred from one substance to another and transformed from one form to another, but it cannot be created or destroyed. This means the total amount of energy in the universe remains constant. For example, in biological systems, solar energy from the sun is converted into chemical energy through photosynthesis in plants. This chemical energy can then be transferred to animals when they consume plants, and further transformed into ATP during cellular respiration. Despite these transformations and transfers, the total energy remains unchanged.

What is entropy in the context of the Second Law of Thermodynamics?

Entropy is a measure of disorder or randomness in a system. According to the Second Law of Thermodynamics, the entropy of the universe tends to increase over time. This means that energy transfers are never 100% efficient, and some energy is always lost as heat, contributing to increased disorder. For instance, when energy is transferred from the sun to plants and then to animals, some of it is lost as heat, increasing the overall entropy. Living organisms can input energy to create order within their systems, but the natural tendency is towards greater disorder.

How does the Second Law of Thermodynamics apply to biological systems?

The Second Law of Thermodynamics states that energy transfers are never 100% efficient, leading to an increase in universal entropy. In biological systems, this means that with every energy transfer, such as from sunlight to plants (photosynthesis) and from plants to animals (consumption), some energy is lost as heat. This heat is not usable by organisms and contributes to the overall increase in disorder. Despite this, living organisms can input energy to maintain order within their systems, such as using ATP to power cellular processes. However, the natural tendency is for systems to move towards greater disorder.

Can energy be created or destroyed according to the First Law of Thermodynamics?

No, according to the First Law of Thermodynamics, energy cannot be created or destroyed. It can only be transferred from one substance to another or transformed from one form to another. This principle is known as the conservation of energy. For example, in photosynthesis, solar energy is transformed into chemical energy stored in glucose. When animals consume plants, this chemical energy is transferred and transformed into ATP, which cells use for various functions. Despite these transformations, the total amount of energy remains constant.

Why is 100% efficient energy conversion impossible according to the Second Law of Thermodynamics?

According to the Second Law of Thermodynamics, 100% efficient energy conversion is impossible because some energy is always lost as heat during energy transfers. This heat is a form of kinetic energy that is transferred between objects with different temperatures and is not usable by organisms. For example, when energy is transferred from the sun to plants and then to animals, some of it is lost as heat at each step. This loss of energy as heat contributes to the increase in universal entropy, meaning the overall disorder of the universe increases with each energy transfer.