Question

What do we mean by thermodynamics? What is the first law of thermodynamics?

Short answer

Thermodynamics is a branch of physics that studies the relationships between heat and other forms of energy, focusing on the transfer of energy within a system or to its surroundings. The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only converted from one form to another. Mathematically, it can be expressed as \(ΔE_{system} = Q - W\), where \(ΔE_{system}\) 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. Sign convention is important for determining energy flow direction, with positive \(Q\) representing heat added to the system and positive \(W\) indicating work done by the system on its surroundings.

Step-by-step solution

Define Thermodynamics

Thermodynamics is a branch of physics that deals with the relationships between heat and other forms of energy. Its main aim is studying the transfer of energy within a system or to its surroundings under various real-life conditions. Thermodynamics can be applied to a wide variety of processes, including engines, refrigeration, and phase changes of substances.

Introduce the First Law of Thermodynamics

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

Express the First Law of Thermodynamics Mathematically

The first law of thermodynamics can be expressed mathematically as follows: \[ ΔE_{system} = Q - W \] Where: \(ΔE_{system}\) is the change in the 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.

Explain the Sign Convention

When working with the first law of thermodynamics, the sign convention is crucial when determining the direction in which energy flows. - If heat is added to the system, \(Q\) is positive; if heat is removed from the system, \(Q\) is negative. - If work is done by the system on its surroundings, \(W\) is positive; if work is done on the system by its surroundings, \(W\) is negative. Understanding the sign convention is necessary to apply the first law of thermodynamics correctly to various situations.

Apply the First Law of Thermodynamics in an Example

Let's consider an example of a system that involves a chemical reaction and apply the first law of thermodynamics to analyze it. Suppose a reaction releases 500 J of heat and does 300 J of work on its surroundings. To find the change in internal energy of the system, we can use the equation mentioned above: \[ ΔE_{system} = Q - W \] \[ ΔE_{system} = 500 J - 300 J \] \[ ΔE_{system} = 200 J \] In this case, the internal energy of the system increases by 200 J during the reaction, as energy is conserved and transformed from other forms into internal energy.

Key concepts

Understanding Thermodynamics

Thermodynamics is the branch of physics that explores the movement and conversion of energy, particularly heat energy, in various systems. It provides vital knowledge for understanding how energy is used and transformed in everything from engines to ecosystems. Essentially, thermodynamics helps us make sense of how energy is input, stored, and transferred in any given scenario.

One classical real-world application of thermodynamics is in studying the efficiency of heat engines—devices that convert heat energy into mechanical work, like the engine in a car. By understanding thermodynamics, engineers can design machines that use energy more efficiently, reducing energy waste and improving performance.

Energy Conservation in Thermodynamics

The principle of energy conservation is a cornerstone of thermodynamics. This principle asserts that energy can neither be created nor destroyed; it can only change form or be transferred from one place to another. The first law of thermodynamics is the formal statement of this principle within the context of heat and work interactions.

In daily life, energy conservation is observed when electrical energy from a battery is converted into light and heat in a bulb, or when gravitational potential energy is transformed into kinetic energy as an object falls. Every process happening around us follows the law of energy conservation, making sure that the total energy in a closed system remains constant.

Internal Energy: The Backbone of Thermodynamical Systems

Internal energy is a measure of all the energy contained within a system, including kinetic and potential energies at the molecular level. This encompasses the energy stored within chemical bonds, as well as the energy particles possess due to motion or vibration.

Any changes to a system's internal energy can result from heating (adding or removing energy as heat) or doing work (where energy is transferred through force acting over a distance). For instance, when water is heated to boiling, its internal energy increases, as does the speed of its molecules. Understanding internal energy is crucial for explaining how and why temperature changes occur, as well as for predicting the behavior of substances under various conditions.

Thermodynamic Processes: How Energy Transforms and Transfers

Thermodynamic processes refer to the ways in which a system exchanges energy with its surroundings. These processes, whether occurring naturally or in engineered systems, follow the laws of thermodynamics, with the first law governing how energy is conserved during the changes.

Common types of thermodynamic processes include isothermal (occurring at constant temperature), adiabatic (no heat exchange with the surroundings), isobaric (constant pressure), and isochoric (constant volume). A deeper comprehension of these processes aids in the prediction of system behavior, such as how an air conditioner cools a room (an adiabatic process) or how a pressure cooker raises the boiling point of water (an isobaric process). These examples show the ubiquitous nature of thermodynamic processes in our everyday lives.