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# First law of thermodynamics equation

Equation for the first law of thermodynamics. Created by David SantoPietro.

## Want to join the conversation?

• What are adibatic isothermal isochoric
• "Adiabatic", "isothermal", and "isochoric" refer to different processes involving manipulation of enclosed ideal gases.

An adiabatic process refers to a situation where a gas is manipulated without losing or gaining heat energy. This mean you can compress or expand the gas, and the pressure and temperature can change, but no heat is transferred into or out of the system. To do this, you must completely insulate your system, and the work done on or by the gas must be done quickly enough so that the heat energy has no time to escape.

An isothermal process is a process where a gas is manipulated in such a way that its temperature stays the same. This means that you can compress or expand the gas to increase or decrease the pressure, but it must be done really slowly so that the temperature will always stay in equilibrium with the gas' surroundings, or otherwise at such a rate that the temperature of the gas stays the same at any point in the process.

An isochoric process is a process where a gas is manipulated in such a way that its volume does not change. This means you can add or remove heat energy to change the temperature of the gas, which in turn changes the pressure of the gas inside the container.

There is also a fourth process called an isobaric process, in which the pressure stays the same. This is achieved by letting the gas expand if the temperature increases, by increasing the volume of the container, or by reducing the volume if the gas' temperature decreases.

I suggest you watch the videos on PV diagrams later in this list if you have yet to do so, to get a better explanation. :)
• In zeorth law of thermodynamics objects 1and 2are made in contact and they are in thermal equilibrium. When second object contacts with third its temperature should decrease why it is same as 1 object
(1 vote)
• The Zeroth Law actually states that if object 1 is in thermal equilibrium with objects 2 and 3, then 2 and 3 are also in thermal equilibrium
• is value of U always positive? or is there any process where it can be zero or negative?
• U is always positive, because it's not possible to have less-than-zero-energy. Delta U (change in U) however can be positive, negative, or zero, as it represents the change in energy.
• what happens when work is done on gas molecules?

Also if the collision were to move many gas molecules, could the gas molecules collide into each other eventually cancelling out the energy that all the gas molecules have

Im so confused to what to imagine when work is done on a gas
• you can't cancel the energy of gas because when you try to the other gas molecules will transfer their energy, to that other gas molecule.
(1 vote)
• Molecules are also subject to intermolecular interactions (repulsive or attractive forces/energies).....Anyway excellent video...Thank you...
• Is this physics or chemistry?
• this is physics when you refer to plain energy, but chemistry when you talk about thermal energy.
(1 vote)
• For the AP Physics 2 test, will they use the version with the plus sign or the version with the minus sign? or both?
• Why is heat represented by a Q?
(1 vote)
• Q came from the calorist's theories of heat being a quality of matter. Q means quantity. Even though the theory of heat was disproven, the term "calorie" and the symbol q remained.In the early days of thermodynamics, the nature of heat was not well understood, and it took some years of experiments and learned discussion to establish exactly what 'heat' was. It is possible that the symbol Q was used to denote a catch-all 'quantity' until its characteristics had been better determined. It appears that, for a very long time, heat was considered to a material that existed in all bodies and materials, with a tendency to flow from areas that were hot to those that were cooler. Before the development of thermodynamics, the then current theory of caloric pictured heat as an elastic, almost weightless, liquid. In discussions of this theory, it is noticeable that the phrase 'the quantity of caloric' occurs frequently, as opposed to other quantities which tended to be referred to simply by their name eg 'the pressure'. This may have led to the adoption of Q for heat energy, particularly if H was then in use for some other quantity.