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# this law states that, in any process, energy is neither created nor destroyed. it can only be converted from one form to another.

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## Law of conservation of energy

In other languages: Français

The law of conservation of energy states that energy can neither be created nor destroyed - only converted from one form of energy to another. This means that a system always has the same amount of energy, unless it's added from the outside. This is particularly confusing in the case of non-conservative forces, where energy is converted from mechanical energy into thermal energy, but the overall energy does remain the same. The only way to use energy is to transform energy from one form to another.

The amount of energy in any system, then, is determined by the following equation:

U T = U i +W+Q UT=Ui+W+Q U T UT

is the total internal energy of a system.

U i Ui

is the initial internal energy of a system.

W W

is the work done by or on the system.

Q Q

is the heat added to, or removed from, the system.

It is also possible to determine the change in internal energy of the system using the equation:

ΔU=W+Q ΔU=W+Q

This is also a statement of the first law of thermodynamics.

While these equations are extremely powerful, they can make it hard to see the power of the statement. The takeaway message is that energy cannot be created from nothing. Society has to get energy from somewhere, although there are many sneaky places to get it from (some sources are primary fuels and some sources are primary energy flows).

Early in the 20th century, Einstein figured out that even mass is a form of energy (this is called mass-energy equivalence). The amount of mass directly relates to the amount of energy, as determined by the most famous formula in physics:

E=m c 2 E=mc2 E E

is the amount of energy in an object or system.

m m

is the mass of the object or system.

c c

is the speed of light, roughly

3× 10 8 m/s 3×108m/s .

First law of thermodynamics

Internal energy Work Heat Carnot efficiency

Or explore a [random page]

To learn more about the physics of the law of conservation of energy, please see hyperphysics or for how this relates to chemistry please see UC Davis's chem wiki.

## Authors and Editors

Ethan Boechler, Allison Campbell, Jordan Hanania, James Jenden, Jason Donev

Last updated: September 27, 2021

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Source : energyeducation.ca

## Fact or Fiction?: Energy Can Neither Be Created Nor Destroyed

Scientific American is the essential guide to the most awe-inspiring advances in science and technology, explaining how they change our understanding of the world and shape our lives.

SPACE & PHYSICS

## Fact or Fiction?: Energy Can Neither Be Created Nor Destroyed

Is energy always conserved, even in the case of the expanding universe?

By Clara Moskowitz on August 5, 2014

The conservation of energy is an absolute law, and yet it seems to fly in the face of things we observe every day. Sparks create a fire, which generates heat—manifest energy that wasn’t there before. A battery produces power. A nuclear bomb creates an explosion. Each of these situations, however, is simply a case of energy changing form. Even the seemingly paradoxical dark energy causing the universe’s expansion to accelerate, we will see, obeys this rule.

The law of conservation of energy, also known as the first law of thermodynamics, states that the energy of a closed system must remain constant—it can neither increase nor decrease without interference from outside. The universe itself is a closed system, so the total amount of energy in existence has always been the same. The forms that energy takes, however, are constantly changing.

Potential and kinetic energy are two of the most basic forms, familiar from high school physics class: Gravitational potential is the stored energy of a boulder pushed up a hill, poised to roll down. Kinetic energy is the energy of its motion when it starts rolling. The sum of these is called mechanical energy. The heat in a hot object is the mechanical energy of its atoms and molecules in motion. In the 19th century physicists realized that the heat produced by a moving machine was the machine’s gross mechanical energy converted into the microscopic mechanical energy of atoms. Chemical energy is another form of potential energy stored in molecular chemical bonds. It is this energy, stockpiled in your bodily cells, that allows you to run and jump. Other forms of energy include electromagnetic energy, or light, and nuclear energy—the potential energy of the nuclear forces in atoms. There are many more. Even mass is a form of energy, as Albert Einstein’s famous E = mc2 showed.

Fire is a conversion of chemical energy into thermal and electromagnetic energy via a chemical reaction that combines the molecules in fuel (wood, say) with oxygen from the air to create water and carbon dioxide. It releases energy in the form of heat and light. A battery converts chemical energy into electrical energy. A nuclear bomb converts nuclear energy into thermal, electromagnetic and kinetic energy.

As scientists have better understood the forms of energy, they have revealed new ways for energy to convert from one form to another. When physicists first formulated quantum theory they realized that an electron in an atom can jump from one energy level to another, giving off or absorbing light. In 1924 Niels Bohr, Hans Kramers, and John Slater proposed that these quantum jumps temporarily violated energy conservation. According to the physicists, each quantum jump would liberate or absorb energy, and only on average would energy be conserved.

Einstein objected fervently to the idea that quantum mechanics defied energy conservation. And it turns out he was right. After physicists refined quantum mechanics a few years later, scientists understood that although the energy of each electron might fluctuate in a probabilistic haze, the total energy of the electron and its radiation remained constant at every moment of the process. Energy was conserved.

Modern cosmology has offered up new riddles in energy conservation. We now know that the universe is expanding at a faster and faster rate—propelled by something scientists call dark energy. This is thought to be the intrinsic energy per cubic centimeter of empty space. But if the universe is a closed system with a finite amount of energy, how can it spawn more empty space, which must contain more intrinsic energy, without creating additional energy?

It turns out that in Einstein’s theory of general relativity, regions of space with positive energy actually push space outward. As space expands, it releases stored up gravitational potential energy, which converts into the intrinsic energy that fills the newly created volume. So even the expansion of the universe is controlled by the law of energy conservation.

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Source : www.scientificamerican.com

## The Laws of Thermodynamics

The Laws of Thermodynamics The Three Laws of Thermodynamics

The laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems.

### LEARNING OBJECTIVES

Discuss the three laws of thermodynamics.

### Key Points

The first law, also known as Law of Conservation of Energy, states that energy cannot be created or destroyed in an isolated system.

The second law of thermodynamics states that the entropy of any isolated system always increases.

The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

### System or Surroundings

In order to avoid confusion, scientists discuss thermodynamic values in reference to a system and its surroundings. Everything that is not a part of the system constitutes its surroundings. The system and surroundings are separated by a boundary. For example, if the system is one mole of a gas in a container, then the boundary is simply the inner wall of the container itself. Everything outside of the boundary is considered the surroundings, which would include the container itself.

The boundary must be clearly defined, so one can clearly say whether a given part of the world is in the system or in the surroundings. If matter is not able to pass across the boundary, then the system is said to be closed; otherwise, it is open. A closed system may still exchange energy with the surroundings unless the system is an isolated one, in which case neither matter nor energy can pass across the boundary.

A Thermodynamic System: A diagram of a thermodynamic system

### The First Law of Thermodynamics

The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another. For example, turning on a light would seem to produce energy; however, it is electrical energy that is converted.

A way of expressing the first law of thermodynamics is that any change in the internal energy (∆E) of a system is given by the sum of the heat (q) that flows across its boundaries and the work (w) done on the system by the surroundings:

Δ E = q + w ΔE=q+w

This law says that there are two kinds of processes, heat and work, that can lead to a change in the internal energy of a system. Since both heat and work can be measured and quantified, this is the same as saying that any change in the energy of a system must result in a corresponding change in the energy of the surroundings outside the system. In other words, energy cannot be created or destroyed. If heat flows into a system or the surroundings do work on it, the internal energy increases and the sign of q and w are positive. Conversely, heat flow out of the system or work done by the system (on the surroundings) will be at the expense of the internal energy, and q and w will therefore be negative.

### The Second Law of Thermodynamics

The second law of thermodynamics says that the entropy of any isolated system always increases. Isolated systems spontaneously evolve towards thermal equilibrium—the state of maximum entropy of the system. More simply put: the entropy of the universe (the ultimate isolated system) only increases and never decreases.

A simple way to think of the second law of thermodynamics is that a room, if not cleaned and tidied, will invariably become more messy and disorderly with time – regardless of how careful one is to keep it clean. When the room is cleaned, its entropy decreases, but the effort to clean it has resulted in an increase in entropy outside the room that exceeds the entropy lost.

### The Third Law of Thermodynamics

The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero. The entropy of a system at absolute zero is typically zero, and in all cases is determined only by the number of different ground states it has. Specifically, the entropy of a pure crystalline substance (perfect order) at absolute zero temperature is zero. This statement holds true if the perfect crystal has only one state with minimum energy.

## Spontaneous and Nonspontaneous Processes

Spontaneous processes do not require energy input to proceed, whereas nonspontaneous processes do.

### LEARNING OBJECTIVES

Describe the differences between spontaneous and nonspontaneous processes.

### Key Points

A spontaneous process is capable of proceeding in a given direction without needing to be driven by an outside source of energy.

The laws of thermodynamics govern the direction of a spontaneous process, ensuring that if a sufficiently large number of individual interactions are involved, then the direction will always be in the direction of increased entropy.

An endergonic reaction (also called a nonspontaneous reaction) is a chemical reaction in which the standard change in free energy is positive and energy is absorbed.

Source : courses.lumenlearning.com

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James 10 month ago

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