Laws of thermodynamics

What is an open system in thermodynamics?

An open system can exchange both energy and matter with its surroundings. Humans are examples of open systems because we take in chemical energy from food and release energy through movement, heat, and waste.

Give an example of energy and matter exchange in a human.

Eating a carrot (matter and chemical energy intake) and breathing out carbon dioxide (matter and energy output).

What is a closed system in thermodynamics?

A closed system can exchange energy but not matter with its surroundings. For example, a tightly covered pot on a stove approximates a closed system.

What is an isolated system in thermodynamics?

An isolated system cannot exchange either matter or energy with its surroundings. A well-insulated drink cooler approximates an isolated system, as energy exchange with the environment is minimal.

What is the First Law of Thermodynamics?

Energy cannot be created or destroyed; it can only change form or be transferred from one object to another.

Give examples of the First Law in biological or everyday systems.

Light bulbs convert electrical energy to light and heat; pool balls transfer kinetic energy; plants convert sunlight (radiant energy) into chemical energy; humans convert chemical energy from food into kinetic energy for movement.

Why are energy transfers never completely efficient?

Because in every transfer, some energy is lost as heat (thermal energy), which is energy not available to do work.

What is the Second Law of Thermodynamics?

In every energy transfer or transformation, some energy becomes unusable (often as heat), increasing the entropy of the universe and reducing the amount of energy available to do work.

Why can't heat be completely converted into other forms of energy with 100% efficiency?

Because energy spontaneously flows from hot to cold, and once dispersed as heat, it is statistically improbable to completely reconcentrate for work.

How does heat increase the randomness of the universe?

When heat flows from a hot object to a cooler one, molecular speeds even out, creating a more disordered system with more possible states than the original temperature-separated configuration.

What is entropy?

Entropy is the degree of randomness or disorder in a system.

What is a biology-relevant statement of the Second Law of Thermodynamics?

Every energy transfer increases the entropy of the universe and reduces the amount of usable energy available to do work, although some processes may leave overall entropy unchanged.

How do living organisms maintain local order while increasing universal entropy?

Organisms use energy to decrease local entropy (building cells, tissues, organs), but energy transfer produces heat and waste molecules, increasing the entropy of the surroundings, resulting in a net increase in universal entropy.

Provide an example of entropy increase in humans during walking.

Chemical energy from glucose is converted into kinetic and potential energy for movement, but much is released as heat and small molecules (CO₂, water), increasing the entropy of the surroundings.

Why is local decrease in entropy possible in living systems?

Local decreases are possible only with energy input, where some of that energy is converted into heat or other non-usable forms, ensuring the total entropy of the universe increases.

What is the net effect of energy use in biological systems?

The combination of local order creation (decreasing entropy) and energy transfer (increasing entropy of surroundings) results in an overall increase in universal entropy.

What happens to entropy when an organism dies?

Once dead, the organism can no longer maintain order; matter and energy disperse, increasing the entropy of the universe.

What does it mean for energy to be "unusable"?

Energy is unusable when it cannot be converted to perform work, often because it is dispersed as heat in an equilibrated system and cannot be captured or concentrated.

What is the significance of equilibrium in thermodynamics?

Reaching equilibrium means reactions have maximized entropy; living organisms expend energy to resist equilibrium and maintain order.

How does friction relate to entropy?

Friction generates heat during energy transfers, increasing the disorder (entropy) of the universe.

Can energy be reused forever to perform work?

No, energy cannot be used indefinitely. Once a system reaches equilibrium, energy flows can no longer do work.

What is "heat death" of the universe?

The state when the universe reaches equilibrium, no usable energy remains, and all processes stop.

What is the relationship between entropy and energy availability?

As entropy increases, the amount of usable energy available to do work decreases.

How does chemical energy in macromolecules relate to entropy in metabolism?

Breaking down complex molecules (like glucose or macromolecules in food) produces small molecules and heat, increasing the entropy of the surroundings.

How is entropy linked to the direction of processes?

Processes naturally proceed from lower to higher entropy, giving thermodynamic directionality to chemical reactions and energy transformations.

Can a computer be considered a closed system?

No, because it gives off heat and exchanges energy with its environment, making it an open system rather than a truly closed system.

What is the unit of measurement for entropy?

Entropy is measured in Joules per Kelvin (J/K).

How does the Second Law of Thermodynamics relate to the expansion of the universe?

Increasing heat and kinetic energy (entropy) can create pressure in enclosed systems; analogously, the buildup of heat/entropy in the universe contributes to its expansion.

How do living systems maintain high organization over time?

Through constant energy input, which allows local decreases in entropy while increasing the entropy of the surroundings, maintaining overall net increase in universal entropy.

Summarize the key difference between the First and Second Laws of Thermodynamics.

The First Law concerns energy conservation (total energy remains constant), while the Second Law concerns energy usability and process directionality (entropy increases, usable energy decreases).