The difference between the first law of thermodynamics and the two forms of integration

The first equation in the diagram is a description of the first law of thermodynamics: q [heat absorbed in the system] = d(e) [internal energy of the system] + w [work done by the system], but q and w themselves are already"Energy conversion"It is worth mentioning that q and w are process-related, not state functions, and all conditions are true.

The second formula refers to:"Internal energy (e)."In"Ideal gas"The formula that works at the time is not applicable at other times. The definition of work (w) is derived from -int(f*dx), as long as it is not a non-conservative force, such as a Mocha force, etc., pdv. can be usedIn addition, there are also corresponding ways to do work in other ways"p"with"dv"of points, such as:

HDM is even the work done by magnetism, etc.

The first law of thermodynamics applies to: any change in a closed system.

Introduction to the First Law of Thermodynamics:

The first law of thermodynamics is the law of conservation and transformation of energy in the field of thermal phenomena, which reflects the conservation of different forms of energy in the process of transfer and conversion.

It is expressed as: The increase in the internal energy of the object is equal to the sum of the heat absorbed by the object and the work done on the object. That is, heat can be transferred from one object to another, and it can also be converted to and from mechanical energy or other energy, but during the conversion process, the total value of the energy remains the same.

Its generalization and essence is the famous law of conservation of energy.

This law has been verified by many physicists such as Meyer and Joule. It was only in the middle of the nineteenth century that it was established in the form of scientific laws on the basis of long-term production practice and a large number of scientific experiments.

Scope of application:

The system must be closed, and open systems with material exchange are not considered by the first law of thermodynamics. That is, the basic definition cannot be used.

The first law of thermodynamics is essentially equivalent to the law of conservation of energy, and is a universal law that applies to all systems in the macrocosm and microcosm, and to all forms of energy.

Since 1850, the law of conservation of energy has been recognized by the scientific community as one of the universal laws of nature. The law of conservation and transformation of energy can be formulated as:

All matter in nature has energy, and energy comes in various forms, and can be transformed from one form to another, but in the process of transformation, the total value of energy remains the same.

The first law of thermodynamics is a special form of the law of conservation and transformation of energy in the field of thermal phenomena, which is a summary of human experience and one of the most basic laws of thermodynamics.

The law of conservation of energy, the first law of thermodynamics, states that the total energy in a closed (isolated) system remains constant. Generally speaking, the total energy is no longer just the sum of kinetic energy and potential energy, but the total amount of rest energy (intrinsic energy), kinetic energy, and potential energy.

The law of conservation of energy states that the total energy of a system can only change by the amount of energy transferred to or from the system. The total energy is the sum of the mechanical energy, thermal energy, and any form of internal energy other than thermal energy of the system.

Significance of the law of conservation of energy: The law of conservation of energy is a universal basic law of nature, and it is a powerful force for people to understand nature and use nature.

What is the first law of thermodynamics is as follows:

1. The law of conservation of energy.

The law of conservation of energy, the first law of thermodynamics, states that the total energy in a closed system remains constant. Generally speaking, the total energy is no longer just the sum of kinetic energy and potential energy, but the total amount of stationary energy, kinetic energy and potential energy.

The law of conservation of energy can be expressed as follows: the change in the total energy of a system can only be equal to the amount of energy transferred to or from the system. The total energy is the sum of the mechanical energy, thermal energy, and any form of internal energy other than thermal energy of the system.

2. The law of conservation of momentum.

A system is not subject to an external force or the resultant external force is zero, and the momentum of the system remains the same. i.e. δp1 = -δp2

3. The law of conservation of angular momentum is stupid.

For a particle, the angular momentum theorem can be expressed as follows: the microquotient of the angular momentum of the particle to the fixed point to the time is equal to the moment of the force acting on the particle.

Characteristics of the law of conservation of momentum.

Vector. Momentum is a vector quantity. The equation for the law of conservation of momentum is a vector equation. In general, after the positive direction is specified, the physical quantities that can determine the direction are always represented as "+" or "-".

Only the size of the physical quantity is substituted into the stall: the physical quantity that cannot determine the direction can be represented by letters, if the calculation result is "+", it means that its direction is the same as the specified positive direction, and if the calculation result is "-", it means that its direction is opposite to the specified positive direction.

For the process of small changes Q = U + W, for the reversible process Q = U + PDV (1 state integral to 2 states).

Understanding of the First Law of Thermodynamics.

The law of conservation of energy is applied to thermodynamics, which is the first law of thermodynamics. In other words, the first law of thermodynamics is the specific quantitative relationship between the law of energy transformation and conservation in the process of thermal phenomena, that is, the quantitative relationship between internal energy and other forms of energy. This law states that in the process of changing any thermodynamic system from one state to another, part of the heat transferred from the outside to the system is used to increase the internal energy of the system, and the other part is used to do work on the outside of the system.

The numerical expression of the first law of thermodynamics is: δe=w+q, where δe represents the amount of internal energy change of the system, w represents the work done by the outside on the system, and q represents the heat absorbed by the outside world. From the above equation, it can be seen that the increase in the internal energy of the system is equal to the sum of the heat absorbed by the system from the outside and the work done by the outside on the system.

When using this law, it is necessary to pay attention to the symbolic treatment of three quantities: the external work on the system, w takes the positive value, the system does the work externally w takes the negative value, if the volume of the system does not change, then w = 0;The system absorbs heat from the outside, Q takes a positive value, and the system exerts heat from the outside, and Q takes a negative value; When the internal energy of the system increases, δe takes a positive value, and when the internal energy of the system decreases, δe takes a negative value.

In refrigeration technology, the first law of thermodynamics can be used to analyze the quantitative changes of thermal energy and mechanical energy and their distribution relationships in various thermal processes. For example, when applying the first law of thermodynamics to the analysis of the refrigeration cycle, it can be concluded that in the compression refrigeration cycle, the mechanical energy expended plus the amount of cold obtained from the cryogenic heat source must be equal to the amount of heat released by the refrigerant to the cooling water or air in the condenser.

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Basic content: heat can be converted into work, and work can also be converted into heat; Consuming a certain amount of work will produce a certain amount of heat, and when a certain amount of heat disappears, a certain amount of work will also be produced.

The concrete manifestation of the universal law of energy conversion and conservation in all macroscopic processes involving thermal phenomena. One of the fundamental laws of thermodynamics.

The first law of thermodynamics is a formulation of the law of conservation and transformation of energy. The first law of thermodynamics states that heat energy can be transferred from one object to another and can also be converted to and from mechanical energy or other energy, and the total value of the energy does not change during the transfer and conversion.

It is the internal energy that characterizes the energy of a thermodynamic system. Through work and heat transfer, the system exchanges energy with the outside world, causing some changes in internal energy. According to the universal law of conservation of energy, after the system reaches the final state through any process from the initial state, the increment of the internal energy δu should be equal to the difference between the heat q transferred by the outside world to the system and the work done by the system to the outside world a, i.e., u u δu q a or q δu a, which is the expression of the first law of thermodynamics.

If, in addition to work and heat transfer, there is also energy z brought in by matter entering the system from the outside world, it should be δu q a z. Of course, the above δu, a, q, and z can all be positive or negative. For infinitesimal processes, the differential expression of the first law of thermodynamics is .

dq du da is a state function because u is a state function and du is a full differential; Q and A are process quantities, and DQ and DA only indicate that the smallest quantities are not fully differential, and the symbol D is used to show the difference. In addition, because δu or du only involves the initial and final states, only the initial and final states of the system are required to be equilibrium, regardless of whether the intermediate state is equilibrium or not.

Another formulation of the first law of thermodynamics is that the first type of perpetual motion machine is impossible. This is a machine that many people fantasize about building that can work continuously without any fuel or power, and that can create something out of nothing and provide a steady stream of energy.

Obviously, the first type of perpetual motion machine violates the law of conservation of energy.