How to understand the relationship between temperature, heat and internal energy?

Heat refers to the energy converted during the energy conversion process due to the presence of temperature differences. And this conversion process is called heat exchange or heat transfer. The metric system for heat is joules.

The relationship between heat and heat energy is like the relationship between work done and mechanical energy. If thermal equilibrium has not yet been reached between the two regions, then heat is transferred from the hot place in the middle to the lower one. Any substance has a certain amount of internal energy, which is related to the disordered movement of the atoms and molecules that make up the substance.

When two substances of different temperatures are in thermal contact, they exchange internal energy until the temperature of the two bodies is the same, that is, thermal equilibrium is reached. Here, the amount of energy transferred is equal to the amount of heat exchanged. Many people confuse heat with internal energy, but in fact, heat refers to the change of internal energy and the work done by the system.

Heat describes the flow of energy, while internal energy describes energy itself. A good understanding of the difference between heat and internal energy is the key to understanding the first law of thermodynamics. The energy transferred between objects in the process of heat transfer Heat is related to the process, i.e., endothermic or exothermic must be carried out in a certain process When an object is in a certain state, it cannot be said how much heat it contains

The temperature of an object (mass m) changes to t through a certain process, and the heat it absorbs (or emits out) q=cm· t

where c is the specific heat (capacitance) associated with this process

The unit of heat is the same as the unit of work and energy The unit of heat in the International System of Units is joules (abbreviated as coke, the symbol is j) Historically, the unit of heat has been defined as the card, and it is currently only used as an auxiliary unit of energy, 1 card = joule

The equilibrium relationship between the heat absorbed by a certain area and the heat released and stored in a certain period of time.

Temperature is a sign of the average kinetic energy of a molecule, heat is the amount of process, and internal energy is the amount of state. Of course, under the same conditions of other conditions, the higher the temperature, the greater the internal energy, and there are two ways to change the internal energy of the object, one is to do work, the other is heat transfer, in a process, the loss of heat and the reduction of internal energy are equal in value, but it cannot be considered that heat is equivalent to internal energy, and there is an essential difference between the two in a physical sense.

Under other conditions of constant condition, the higher the temperature of the object, the greater the internal energy, the smaller the temperature, the smaller the internal energy, the lower the temperature, the loss of internal energy, it is possible that this part of the internal energy is converted into heat, the more the temperature decreases, the more heat is converted.

Difference Between Temperature, Internal Energy and Heat:

1. The concept is different.

Temperature: Temperature is a physical quantity that indicates how hot or cold an object is, and microscopically it is the intensity of the thermal motion of the molecules of an object.

Heat: Heat refers to the thermal interaction between the system and the outside world when the change of the state of the system is due to the destruction of the thermal equilibrium conditions, that is, when there is a temperature difference between the system and the outside world.

Internal energy: Generally refers to all the energy in an object.

2. The scope of coverage is different.

Temperature: From the point of view of molecular kinematics, temperature is a sign of the average kinetic energy of the molecular motion of an object.

Internal energy: including the energy of molecular thermal motion, the potential energy of interaction between molecules, the energy of internal motion of molecules and atoms, and the energy of electric and magnetic fields.

Thermal energy: Essence is the sum of the kinetic energy of the irregular movement of all the molecules inside the object.

3. The unit of representation is different.

Temperature: Fahrenheit (°F), Celsius (°C) and international utility temperature scales.

Calories: The unit of heat is "kcal".

Internal energy: The unit is "joules".

The connection between temperature, internal energy and heat:

1. Temperature and internal energy.

The higher the temperature, the faster the molecules in the object move irregularly, and the greater the average kinetic energy of the molecules, so the more internal energy of the object.

2. Temperature and heat.

Temperature reflects how violently the molecules move irregularly. The more intense the molecular motion, the higher the temperature of the object. Heat is the amount of internal energy transferred during heat transfer. An object with a high temperature emits heat and the internal energy decreases, while an object with a low temperature absorbs heat and the internal energy increases.

3. Quantity and internal energy.

Heat reflects the amount of internal energy transferred during heat transfer. The amount of heat emitted by the object decreases the amount of internal energy; The amount of heat absorbed by the object increases the amount of internal energy.

Apply work. 1. Doing work can change the internal energy of an object. (e.g. drilling wood for fire).

When an external force does positive work on an object, the internal energy of the object increases, and vice versa.

2. Heat transfer can change the internal energy of an object. (e.g., placing ice cubes to cool down objects).

There are three forms of heat transfer: heat conduction, heat convection (generally found in gases and liquids), and heat radiation, which is conditional on a temperature difference between objects.

Work done and heat transfer are equivalent in the effect of changing the internal energy. Work is done to convert other forms of energy, such as mechanical energy, into internal energy; Heat transfer causes the internal energy to be transferred between objects.

Temperature 1) Definition: Temperature is a physical quantity that indicates how hot or cold an object is. 2) Substance:

Temperature is a reflection of the irregular intensity of a large number of molecules inside an object. The higher the temperature, the more intense the movement of molecules inside the object. It is a state quantity.

If two objects are at the same temperature, they are the same as hot and cold. Heat 1) Definition: Heat is the energy transferred in the process of heat transfer, which is called heat.

2) Substance: It is the amount of change in the internal energy of an object during heat transfer. It is a process quantity, it is born in the process of heat transfer, and it is meaningless to talk about heat without heat transfer.

Internal energy 1) Definition: The sum of the kinetic energy and molecular potential energy of all molecules in an object moving irregularly. 2) Substance:

It is the energy contained inside the object, it is unconditional, and any object has internal energy. It is a state quantity. From a microscopic point of view, its size is related to the speed of molecular motion, the distance between molecules, and the number of molecules. Macroscopically, its size is related to the temperature of the object, the volume of the object, and the mass of the object.

There are two ways to change the internal energy of an object: work done and heat transfer. The relationship between temperature and heat1) The object absorbs heat, and the temperature of the object does not necessarily rise. For example:

In the process of melting, vaporization and other changes in the state of matter of the crystal, that is, the object only absorbs heat, but its temperature remains the same. The absorbed energy is only used to change the intermolecular potential energy inside the object, and the average kinetic energy of the molecule does not change. 2) When the temperature of the object increases, the object does not necessarily absorb heat.

For example, in the phenomenon of frictional heat generation, the temperature of the object is increased by doing work, and no heat transfer occurs. Relationship between heat and internal energy 1) The object absorbs heat, and the internal energy of the object increases.

The object absorbs heat, either increases the temperature of the object (increasing the average kinetic energy of the molecules) or changes the microstructure of the object (increasing the potential energy between the molecules). For example, when heating water, before the water boils, the temperature of the water rises as it absorbs heat, and the internal energy of the water increases; When water is boiling, the water is still absorbing heat, and although its temperature remains the same, a part of the water becomes water vapor, and its molecular potential energy increases, and its internal energy increases.

2) The internal energy of the object increases, and the object does not necessarily absorb heat. Because there are two ways to change the internal energy – work done and heat transfer. For example:

When sawing wood with a saw blade, the saw blade and the wood heat up, causing an increase in internal energy. Relationship between temperature and internal energy 1) As the temperature of an object increases, the internal energy increases. As the temperature of the object increases, the thermal motion of the molecules intensifies, and the average kinetic energy of a large number of molecules increases, resulting in an increase in the internal energy of the object.

2) The internal energy of the object increases, and its temperature does not necessarily increase. Because the internal energy of an object is not only related to temperature, but also to volume, mass. Relationship between temperature, heat, and internal energy 1) When the temperature of an object increases, the internal energy increases, but it does not necessarily absorb heat.

2) The object absorbs heat and the internal energy increases, but the temperature does not necessarily increase.

Internal energy: refers to the total energy contained in the interior of the object, which includes not only the kinetic energy of the irregular thermal motion of molecules, the potential energy of the interaction between molecules, but also the energy in the molecule atom, the energy in the nucleus, etc. In thermals, the latter two items do not change due to the fact that in thermal motion.

Therefore, the internal energy generally refers to the first two items. Since the kinetic energy of a molecule is related to temperature, and the potential energy of the interaction between molecules is related to the distance between molecules, the internal energy of an object is related to temperature, the interaction between molecules, and the number of molecules.

Temperature: A physical quantity that indicates how hot or cold an object is. From the point of view of molecular kinetic theory, temperature is a sign of the average kinetic energy of a molecule. The higher the temperature, the greater the kinetic energy of the molecule.

Heat: Refers to the amount of change in internal energy during heat transfer. It is a measure of the change in internal energy in heat transfer.

1.The relationship between temperature and internal energy.

The temperature microscopically reflects the intensity of the irregular movement of a large number of molecules inside the object, and it is related to the kinetic energy of the molecules of the object, and the more intense the thermal motion of the molecules of the object, the higher its temperature. For the same object, the temperature increases, the irregular motion of the molecules accelerates, and its internal energy increases; Conversely, when the temperature decreases, the internal energy decreases. But there are two things to note here:

One is that when the temperature of the object is unchanged, the internal energy may not change, but it may also decrease or increase, for example, the water of 0 solidifies into 0 ice (or the ice of 0 melts into 0 water), although the temperature does not change, but the intensity of molecular movement changes, so the internal energy also changes. Second, the internal energy of an object is not only related to its temperature, but also related to the number of molecules, the type of substance and the distance between molecules.

2.The relationship between heat and internal energy.

The essence of heat is the process of transfer of internal energy. For example, heat transfer occurs between two objects, and a high-temperature object emits 50 J of heat, which means that its internal energy is reduced by 50 J; Similarly, if a low-temperature object absorbs 50J of heat, the internal energy increases by 50J, which is actually 50J of internal energy transferred from a high-temperature object to a low-temperature object.

The object absorbs heat, the molecules move violently, and the internal energy increases, but the increase in internal energy can be achieved not only by endothermy but also by doing work on the object. When we are not clear about the process of internal energy change, we are not sure which way it is achieved.

It is also important to note that heat is a process quantity, while internal energy is a state quantity, so it cannot be said that an object contains heat.

The diagram of the relationship between internal energy, heat and temperature is as follows:

If the temperature of the object increases, the internal energy of the object must increase; (Quality, state unchanged, high temperature, large internal energy).

If the temperature of the object increases, the object must absorb heat; (An increase in the temperature of an object may also be a result of work done on the object by the outside world.) )

If the internal energy of the object increases, the temperature of the object must increase; (As the internal energy of an object increases, the state of matter of the object may have changed, or the mass of the object has changed.) )

If the internal energy of the object increases, the object must have absorbed heat; (The increase in the internal energy of the object may also be due to the work done by the outside world on the object).

If the object absorbs heat, the temperature of the object must increase; (When melting, the temperature of the object remains unchanged).

If the object absorbs heat, then the internal energy of the object must increase. (When absorbing heat, external work may be done, and internal energy may not necessarily increase.) )

The temperature is high enough to combrate the oxygen in the air into flames, and the heat transfer can cause the matter to melt and melt to the extreme, destroying the matter (mass) and energy.

The temperature is low to a certain extent, it can solidify with water or air or water in the body (blood) to transfer cold, ice deficiency and freezing can lead to the fragmentation of matter, cold to the extreme of the empty calendar, and the mass and energy of matter, all life-threatening can change the speed of movement (movement) of objects.

Internal energy, heat, and temperature are the three important physical quantities in thermal. After learning the knowledge of internal energy, most students cannot correctly understand the concept and interrelationship of these three physical quantities, and the differences and connections between the three are summarized as follows to help students understand and apply.

1. The difference between the three.

1.Internal energy is the sum of the kinetic energy and molecular potential energy of all the molecules inside the object to move irregularly.

Inner energy can only say "yes", not "no".It is only quantitatively meaningful when the energy within the object is changed and is associated with work done or heat transfer.

2.Temperature indicates how hot or cold an object is, and from the point of view of molecular kinetic theory, temperature is a sign of the intensity of the thermal motion of the molecule, and for the same object, the temperature can only say "how much" or "how much", and cannot say "have", "no", or "contain", etc.

3.Heat is the amount of heat absorbed or emitted by an object in the process of heat transfer, and its essence is the amount of change in internal energy. Heat is closely linked to heat transfer, and without heat transfer there is no heat.

You can only say "how much you absorb" or "how much you emit out" for heat, and you can't add "have" or "no" or "contain" before the noun of heat

The relationship between the two and the three.

1.The relationship between internal energy and temperature.

A change in the internal energy of an object does not necessarily cause a change in temperature. This is due to the fact that the internal energy of the object changes at the same time, and there is a possibility of biological changes. The internal energy of an object changes when it undergoes a biological change, and the temperature sometimes changes and sometimes it does not.

For example, in the process of melting and solidification of crystals, as well as the process of liquid boiling, although the internal energy changes, the temperature remains the same. The temperature indicates how fast or slow the molecules inside the object move.

Therefore, as the temperature of the object increases, the speed of the irregular motion of the molecules inside it increases, the kinetic energy of the molecules increases, and therefore the internal energy also increases, and vice versa, the temperature decreases, and the internal energy of the object decreases. Therefore, a change in the temperature of an object will inevitably cause a change in internal energy.

2.The relationship between internal energy and heat.

The internal energy of an object changes, but the object does not necessarily absorb or release heat, because there are two ways to change the internal energy of an object: work done and heat transfer. That is, the internal energy of the object changes, either because the object absorbs (or emits out) heat, or it may do work on the object (or the object does work externally).

Whereas, heat is a measure of the change in the internal energy of an object during heat transfer. The object absorbs heat, the internal energy increases, and the object emits heat, and the internal energy decreases. Therefore, the object is endothermic or exothermic and will inevitably cause a change in internal energy.

3.Relationship between heat and temperature.

An object absorbs or emits heat, and the temperature does not necessarily change, because the object is absorbing or releasing heat at the same time, if the object itself undergoes a change in state (such as the melting of ice or the solidification of water).At this point, the object absorbs (or emits heat) but the temperature remains the same.

When the temperature of the object changes, the object does not necessarily absorb or release heat, or it may be due to the work done on the object (or the work done externally on the object) that causes the internal energy of the object to change, and the temperature changes.