# Thermodynamics: Internal Energy, Heat and Work Problem

• AN630078
In summary: I do not think these examples define heat adequately)In summary, internal energy is the total energy of all the molecules in a substance, associated with their random motion. Examples include compressed gases, liquids, solids, and charged batteries. Heat is the energy transferred from one body to another due to a temperature difference. Examples include melting ice with water, the heat from the Sun, and toasting bread. Work is the energy transferred by a system to its surroundings, and an example is a gas expanding and doing work on a piston. These three quantities are linked by the first law of thermodynamics, which states that the change in internal energy (E) is equal to the heat transfer (Q)
AN630078
Homework Statement
When revising questions from a textbook on thermal physics I came across the following problem;
"Distinguish using examples internal energy, heat and work. Of these which may be considered ordered rather than random?"

I am really struggling to find examples for each of these and cannot confidently distinguish which is random/ordered. My textbook is not particular detailed upon this topic and does not provide much clarity which I why I would really appreciate any insight that could be offered.
I have not learnt about the laws of thermodynamics but am marginally familiar with them from reading them in passing.
Thank you for any and all help
Relevant Equations
U=Q-W
Well, internal energy is the sum of the kinetic and potential energies of all the molecules within a given mass of a substance; this energy is associated with the random, disordered motion of the molecules.
An example of internal energy is compressed gases; since gases occupy the total volume of the container in which they are situated their internal energy will vary when their container is greater and will increase when it is smaller. This means that for a gas dispersed in a room it actually has less internal energy than if it were compressed into a cylinder, since its particles will be forced to interact more closely.
Another example may be a batteries; within the charged batteries there is internal energy, on account of the chemical reactions between the heavy metals and acids inside. This internal energy will be greater when its electric charge is complete and less when it has been used.

(I do not think these examples define internal energy adequately)

Heat is the energy transferred from one body to another as the result of a difference in temperature. An example of heat can be witnessed by placing a cube of ice into a glass of water. The heat energy from the water will eventually melt the ice; thus the water itself is a source of heat energy.
Another example, and perhaps the most obvious, would be the Sun itself. The Sun radiates heat in our solar system to warm planet Earth.
Even making a piece of toast is an example of heat; a toaster turns a piece of soft bread into a piece of crispy toast by drawing moisture from the bread using radiant heat energy.
I think that heat is random since heat transfer occurs spontaneously from higher to lower temperature bodies in accordance with the second law of thermodynamics. In thermodynamics, work performed by a system is the energy transferred by the system to its surroundings. An example is a gas confined by a piston in a cylinder.
If the gas is heated it will expand, doing work on the piston; this is one example of how a thermodynamic system can do work. The energy of the gas is transferred to the piston in order to do work. (I do not think is a particularly relative of concise definition either).
I do not know whether work is ordered or random and I have been thinking about it for so long that I cannot firmly take a position in support of either.

These three quantities are linked by the first law of thermodynamics, which is essentially the application of the conservation of energy to heat and thermodynamic processes. The first law of thermodynamics defines the internal energy (E) as equal to the difference of the heat transfer (Q) into a system and the work (W) done by the system;
.

AN630078 said:
Homework Statement:: When revising questions from a textbook on thermal physics I came across the following problem;
"Distinguish using examples internal energy, heat and work. Of these which may be considered ordered rather than random?"

I am really struggling to find examples for each of these and cannot confidently distinguish which is random/ordered. My textbook is not particular detailed upon this topic and does not provide much clarity which I why I would really appreciate any insight that could be offered.
I have not learned about the laws of thermodynamics but am marginally familiar with them from reading them in passing.
Thank you for any and all help
Relevant Equations:: U=Q-W

Well, internal energy is the sum of the kinetic and potential energies of all the molecules within a given mass of a substance; this energy is associated with the random, disordered motion of the molecules.
An example of internal energy is compressed gases;
I would stop right here, although another example is a liquid or solid.
since gases occupy the total volume of the container in which they are situated their internal energy will vary when their container is greater and will increase when it is smaller. This means that for a gas dispersed in a room it actually has less internal energy than if it were compressed into a cylinder, since its particles will be forced to interact more closely.
This applies to real gases, but, in the case of ideal gases, the molecular interactions are negligible, and the only contributor to the internal energy is the random kinetic energy (which doesn't change when the gas volume increases or decreases).
Another example may be a batteries; within the charged batteries there is internal energy, on account of the chemical reactions between the heavy metals and acids inside. This internal energy will be greater when its electric charge is complete and less when it has been used.

(I do not think these examples define internal energy adequately)
Heat is the energy transferred from one body to another as the result of a difference in temperature. An example of heat can be witnessed by placing a cube of ice into a glass of water. The heat energy from the water will eventually melt the ice; thus the water itself is a source of heat energy.
Another example, and perhaps the most obvious, would be the Sun itself. The Sun radiates heat in our solar system to warm planet Earth.
Even making a piece of toast is an example of heat; a toaster turns a piece of soft bread into a piece of crispy toast by drawing moisture from the bread using radiant heat energy.
I think that heat is random since heat transfer occurs spontaneously from higher to lower temperature bodies in accordance with the second law of thermodynamics.
I don't regard heat energy as random since it has direction (from hot to cold), and heat flux can be expressed as a vector quantity.

In thermodynamics, work performed by a system is the energy transferred by the system to its surroundings. An example is a gas confined by a piston in a cylinder.
If the gas is heated it will expand, doing work on the piston; this is one example of how a thermodynamic system can do work. The energy of the gas is transferred to the piston in order to do work. (I do not think is a particularly relative of concise definition either).
I do not know whether work is ordered or random and I have been thinking about it for so long that I cannot firmly take a position in support of either.
In my judgment, work is ordered, because it is force times displacement.
These three quantities are linked by the first law of thermodynamics, which is essentially the application of the conservation of energy to heat and thermodynamic processes. The first law of thermodynamics defines the internal energy (E) as equal to the difference of the heat transfer (Q) into a system and the work (W) done by the system;
.
In my judgment, you did a very nice job of researching and analyzing all this.

## 1. What is internal energy in thermodynamics?

Internal energy is the total energy stored in a system, including the kinetic and potential energies of its particles. It is a state function, meaning it only depends on the current state of the system and not on the path it took to get there.

## 2. How is heat related to internal energy?

Heat is the transfer of thermal energy from one system to another. In thermodynamics, heat is considered a form of energy that can increase the internal energy of a system. When heat is added to a system, its internal energy increases and when heat is removed, its internal energy decreases.

## 3. What is the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, it can only be transferred or converted from one form to another. This means 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.

## 4. How is work defined in thermodynamics?

In thermodynamics, work is defined as the transfer of energy from one system to another due to a force acting on the system. This can include mechanical work, such as pushing or pulling, or electrical work, such as current flowing through a circuit.

## 5. How do you solve problems involving internal energy, heat, and work?

To solve problems involving internal energy, heat, and work, you can use the first law of thermodynamics, which states that the change in internal energy is equal to the heat added to the system minus the work done by the system. You can also use specific equations, such as the ideal gas law, to calculate the change in internal energy, heat, or work for a specific system.

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