First Law of Thermodynamics

The first law of thermodynamics is also known as the law of conservation of energy. It states that energy cannot be created or destroyed, only transformed from one form to another. In other words, the total amount of energy in a closed system remains constant.

Table of Contents:

• First Law of Thermodynamics
• Derivation of the First Law of Thermodynamics
• Applications
• FAQs

The first law of thermodynamics is also known as the law of conservation of energy. It states that energy cannot be created or destroyed, only transformed from one form to another. In other words, the total amount of energy in a closed system remains constant.

This law has important implications for the study of thermodynamics, which deals with the relationships between energy, work, and heat.

The first law of thermodynamics can be expressed mathematically as:

where ΔU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done by the system.

This equation shows that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. If no heat is added or work is done, then the internal energy of the system remains constant.

Here are some examples of the first law of thermodynamics in action:

When a gas is compressed, the work done by the system increases, and the internal energy of the gas increases as well. This is because the compression process increases the pressure of the gas, which results in an increase in its internal energy.

When a battery is used to power a device, the chemical energy stored in the battery is converted into electrical energy, which is then transformed into other forms of energy, such as light or heat. The total amount of energy in the system remains constant, but the form of the energy changes.

When a hot object is placed in contact with a cold object, heat flows from the hot object to the cold object until the two objects reach thermal equilibrium. The total amount of energy in the system remains constant, but the distribution of the energy changes as heat is transferred from one object to the other.

Overall, the first law of thermodynamics is a fundamental principle that governs the behavior of energy in physical systems, and it has numerous applications in fields such as chemistry, physics, and engineering.

Derivation of the First Law of Thermodynamics

The first law of thermodynamics is a fundamental principle of thermodynamics, which states that the total energy in a closed system is conserved. This law is derived from the concept of conservation of energy, which is a fundamental principle of physics. Here is a derivation of the first law of thermodynamics:

Consider a closed system consisting of a fluid contained within a piston-cylinder arrangement,
The system is isolated from the surroundings, which means that no matter or energy can enter or leave the system. The piston can move up and down, allowing the volume of the fluid to change, and the fluid can exchange heat and work with the surroundings.

The first law of thermodynamics states that the change in internal energy of the system (ΔU) is equal to the heat added to the system (Q) minus the work done by the system (W):

where ΔU represents the change in internal energy of the system, Q represents the heat added to the system, and W represents the work done by the system.

To derive this equation, we start with the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another.

In the case of a closed thermodynamic system, the total energy in the system is conserved. Therefore, the change in internal energy of the system must be equal to the energy added to the system (in the form of heat) minus the energy removed from the system (in the form of work).

The heat added to the system is defined as the product of the mass of the fluid (m), the specific heat of the fluid (c), and the change in temperature of the fluid (ΔT):

where Q represents the heat added to the system, m represents the mass of the fluid, c represents the specific heat of the fluid, and ΔT represents the change in temperature of the fluid.

The work done by the system is defined as the product of the force exerted by the piston (F) and the distance moved by the piston (d):

where W represents the work done by the system, F represents the force exerted by the piston, and d represents the distance moved by the piston.

Substituting the equations for Q and W into the first law of thermodynamics equation, we get:

This equation describes the change in the internal energy of the system in terms of the heat added to the system and the work done by the system. It is important to note that the sign convention used for work and heat is such that work done by the system and heat added to the system are positive, and work done on the system and heat removed from the system are negative.

Overall, the first law of thermodynamics is a fundamental principle that governs the behavior of energy in physical systems, and it has numerous applications in fields such as chemistry, physics, and engineering.

The first law of thermodynamics, also known as the law of conservation of energy, applies to living organisms in various ways. Here are some examples:

Metabolism: Living organisms, including plants and animals, undergo metabolic processes that involve the conversion of energy from one form to another. The first law of thermodynamics ensures that the total energy in the system remains constant. In the case of organisms, the energy from food molecules is transformed and utilized for various physiological processes, such as growth, reproduction, and movement.

Energy balance: The first law of thermodynamics governs the energy balance in living organisms. Energy intake through food and sunlight is balanced with energy expenditure through metabolic processes and external work. If energy intake exceeds expenditure, the excess energy is stored as potential energy in the form of fat. Conversely, if energy expenditure exceeds intake, the stored energy is utilized to meet the energy deficit.

Energy transformation: The first law of thermodynamics applies to the conversion of energy between different forms within living organisms. For example, during cellular respiration, the chemical energy stored in glucose molecules is converted into adenosine triphosphate (ATP), which is the energy currency of cells. This conversion involves the transfer of energy from the chemical bonds of glucose to the high-energy bonds of ATP.

Heat production: Living organisms produce heat as a byproduct of metabolic processes. The first law of thermodynamics states that the total energy in a system is conserved, so the energy released during metabolic reactions appears as heat. This heat is essential for maintaining the body temperature of warm-blooded organisms within a narrow range necessary for normal physiological functioning.

Applications of the First Law of Motion

The first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed from one form to another, has numerous applications in various fields. Here are some examples of the applications of the first law of thermodynamics:

1. Heat engines: The first law of thermodynamics is the foundation of the study of heat engines, which convert heat into work. The efficiency of a heat engine is determined by the difference between the heat input and the work output, which can be analyzed using the first law of thermodynamics.

2. Chemical reactions: The first law of thermodynamics is used to study the energy changes that occur during chemical reactions. By measuring the heat transfer and work done in a chemical system, it is possible to determine the change in the internal energy of the system and the heat of the reaction.

3. Phase transitions: The first law of thermodynamics is also used to study phase transitions, such as the melting of ice or the boiling of water. By measuring the heat transfer and work done during a phase transition, it is possible to determine the change in the internal energy of the system.

4. Power plants: The first law of thermodynamics is applied in power plants to calculate the efficiency of energy conversion. For example, in a coal-fired power plant, the heat generated by burning coal is used to produce steam, which then drives a turbine to generate electricity. The efficiency of this process can be analyzed using the first law of thermodynamics.

5. Refrigeration and air conditioning: The first law of thermodynamics is used to analyze the energy transfer in refrigeration and air conditioning systems. These systems work by transferring heat from one location to another, which can be analyzed using the first law of thermodynamics.

Overall, the first law of thermodynamics has numerous applications in various fields, and it is an essential concept in the study of energy and its transformations.

First Law of Thermodynamics FAQS