FIRST LAW OF THERMODYNAMICS - The first law of thermodynamics is also known as the law of conservation of energy, which states energy can transform from one form into another, but can neither be created nor destroyed within an isolated system. Perpetual motion machines of the first kind are impossible, according to the first law of thermodynamics. The states that the total energy of a system and its surroundings remain constant. In other words, it is not possible to construct an engine that will cycle and produce work continuously from nothing.

........................................................................................................................................

First Law of Thermodynamics

Definition

Chemistry Glossary Definition of First Law of Thermodynamics

by Anne Marie Helmenstine, Ph.D. 

The first law of thermodynamics is the physical law which states that the total energy of a system and its surroundings remain constant.

The law is also known as the law of conservation of energy, which states energy can transform from one form into another, but can neither be created nor destroyed within an isolated system.

Perpetual motion machines of the first kind are impossible, according to the first law of thermodynamics.

In other words, it is not possible to construct an engine that will cycle and produce work continuously from nothing.

First Law of Thermodynamics Equation

The equation for the first law can be confusing because there are two different sign conventions in use.

In physics, particularly when discussing heat engines, the change in the energy of a system equals the heat flow in the system from the surroundings minus the work done by the system on the surroundings.

The equation for the law may be written:

ΔU = Q - W

Here, ΔU is the change in the internal energy of a closed system, Q is the heat supplied to the system, and W is the amount of work done by the system on the surroundings.

This version of the law follows the sign convention of Clausius.

However, the IUPAC uses the sign convention proposed by Max Planck. Here, net energy transfer to a system is positive and net energy transfer from a system are negative.

The equation then becomes:

ΔU = Q + W

The IUPAC is the International Union of Pure and Applied Chemistry. It is an international scientific organization, not affiliated with any government. The IUPAC strives to advance chemistry, in part by setting global standards for names, symbols, and units. Nearly 1200 chemists are involved in IUPAC projects. Eight standing committees oversee the Union's work in chemistry.

The Role of IUPAC

The IUPAC was formed in 1919 by scientists and academicians who recognized a need for standardization in chemistry. The predecessor of the IUPAC, the International Association of Chemical Societies (IACS), met in Paris in 1911 to propose issues that needed to be addressed. From the beginning, the organization has sought international cooperation between chemists. In addition to setting guidelines, the IUPAC sometimes helps to resolve disputes. An example is the decision to use the name 'sulfur' instead of both 'sulfur' and 'sulphur'.

Anne Marie Helmenstine, Ph.D.

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/first-law-of-thermodynamics-definition-604343