# Mechanical Engineering - Thermodynamics - Discussion

### Discussion :: Thermodynamics - Section 1 (Q.No.24)

24.

There is no change in internal energy in an isothermal process.

 [A]. Correct [B]. Incorrect

Explanation:

No answer description available for this question.

 Parvez said: (Jun 7, 2013) In isothermal process temperature kept constant. And internal energy function of temperature only.

 Goutham said: (Jun 18, 2013) An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange. In contrast, an adiabatic process is where a system exchanges no heat with its surroundings (Q = 0). In other words, in an isothermal process, the value ΔT = 0 but Q ≠ 0, while in an adiabatic process, ΔT ≠ 0 but Q = 0.

 Ankitrana said: (Sep 3, 2013) Internal energy always zero in isothermal process. Formula. du=Cv*dt.

 Nikhil said: (Jan 7, 2014) Internal energy is function of temperature. So no change in internal energy.

 Carlos Pereira said: (Feb 6, 2014) In fact the answer is wrong. The phase change process is isothermal but the internal energy varies.

 Jibi said: (Jun 1, 2014) This answer is only correct for ideal gases. The question needs to clarify this.

 Aju Sreekumar said: (Oct 20, 2014) Then how 100 celsius. Water changes to 100 degree vapour? Please clarify?

 Satyapal Yadav said: (Jun 9, 2015) Internal energy is the function of temperature so, temperature is the constants until internal energy is the constants.

 Akena said: (Mar 21, 2016) delta U = MC delta T. Internal energy directly depends on temperature.

 Muhammad Ali Durrani said: (Feb 26, 2017) The logic behind this falls deep in the molecular level. Internal Energy is a function of temperature, temperature is a function of the Average Kinetic energy of the ideal gas molecules, and internal energy is a function of the average K.E and P.E at microscopic level, now, if the system is one component and does not involve a phase change (and can be approximated as ideal gas) , then the isothermal process will not change the internal energy because the temperature doesn't change and so are the kinetic energies, which is due to the fact that the energy intake to the system is changed into another form of energy, say for example piston cylinder, if the cylinder is getting heat energy from the surrounding, it will be turned into the work energy. But if the system involves a phase change, it is no longer approximated as an ideal gas, and so the C.P.E of the molecules changes which ultimately expands the or contracts the system and so the internal energy changes (because remember Internal energy is a function of K.E as well as the Chemical Potential Energy).

 Sanket said: (Nov 20, 2017) Internal energy is a function of temperature only for the Ideal gas.

 Ab Harikishore said: (Jul 12, 2018) Option B is correct.

 Holby said: (Dec 4, 2018) The average velocity and molecular activities are directly proportional to the temperature of the gas of the system and as a result of the system leads to higher internal energy. So there are no changes in internal energy in an isothermal process, what internal energy referred here in thermodynamics is (microscopic forms of energy example; electron spin, nuclear spin, molecular vibrations), so microscopic interactions of molecular activities occur only if there is a change in temperatures.