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Can someone explain me, whether are these statements true or false, and why are they such?

  1. When measuring the temperature of a given system, all the thermometers give the same results.

  2. When a system goes from thermodynamic state 1 to state 2, the variation of its internal energy depends on the process that originated the change of state.

Thanks!

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    $\begingroup$ What are your answers and, more importantly, why? $\endgroup$
    – user207455
    May 6 '19 at 10:23
  • $\begingroup$ Unfortunately i don't know but i think that 1 and 2 are true $\endgroup$
    – stream
    May 6 '19 at 10:41
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When measuring the temperature of a given system, all the thermometers give the same results.

Ideally, it is true. As long as the system is in thermal equilibrium with itself (no heat enters or leaves it, and it is allowed unlimited time to settle under its own intrinsic characteristics), the average kinetic energy of all the molecules wouldn't vary throughout the system. Hence, different thermometers should report the same temperature. Read more on this here.

When a system goes from thermodynamic state 1 to state 2, the variation of its internal energy depends on the process that originated the change of state.

No that cannot be true. This just follows from conservation of energy. Internal energy is the sum of kinetic and potential energy for all particles inside a system. There are a special class of functions which do not depend on the path taken by a system to reach the final state and are called state functions. You can arrive at why is internal energy a state function while heat and work are not by simply applying First law of thermodynamics.

In simpler terms, to get from state $A$ to state $B$, the system gains a net amount of energy $\Delta U=U_B−U_A$. It does not matter what the process was to achieve the state $B$. Of course, the total amount of energy transferred through different methods has to be the same $\Delta U$ due to energy conservation.

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  • $\begingroup$ thanks for the explanation $\endgroup$
    – stream
    May 6 '19 at 21:25
  • $\begingroup$ In my view neither your answer and mine, which are essentially the same , should have been down voted. I am up voting yours $\endgroup$
    – Bob D
    May 7 '19 at 15:11
  • $\begingroup$ Yes, I don't understand why the downvote. I agree the answers are basically same. I just wanted to expand on what you stated, and provide links to understand basic laws of thermodynamics. $\endgroup$ May 7 '19 at 15:29
  • $\begingroup$ Yes, and your elaboration was very apt. $\endgroup$
    – Bob D
    May 7 '19 at 18:46
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If I understand statement 1 correctly, it would be true if the system is internally in thermal equilibrium (no temperature gradients exist within the system).

Statement 2 is not true. Internal energy is a system property. The change in internal energy between the same two equilibrium states does not depend on the process(es) that got you from the initial state to the final state.

Hope this helps.

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    $\begingroup$ Why the down vote? $\endgroup$
    – Bob D
    May 7 '19 at 14:52

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