Thermodynamics first law Definition and 36 Threads

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing two kinds of transfer of energy, as heat and as thermodynamic work, and relating them to a function of a body's state, called internal energy.
The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.
For a thermodynamic process without transfer of matter, the first law is often formulated




Δ
U
=
Q

W


{\displaystyle \Delta U=Q-W}
,where



Δ
U


{\displaystyle \Delta U}
denotes the change in the internal energy of a closed system,



Q


{\displaystyle Q}
denotes the quantity of energy supplied to the system as heat, and



W


{\displaystyle W}
denotes the amount of thermodynamic work done by the system on its surroundings. An equivalent statement is that perpetual motion machines of the first kind are impossible.
For processes that include transfer of matter, a further statement is needed: 'With due account of the respective reference states of the systems, when two systems, which may be of different chemical compositions, initially separated only by an impermeable wall, and otherwise isolated, are combined into a new system by the thermodynamic operation of removal of the wall, then





U

0


=

U

1


+

U

2




{\displaystyle U_{0}=U_{1}+U_{2}}
,where




U

0




{\displaystyle U_{0}}
denotes the internal energy of the combined system, and




U

1




{\displaystyle U_{1}}
and




U

2




{\displaystyle U_{2}}
denote the internal energies of the respective separated systems.'

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  1. Z

    Chemistry How to understand the energy involved in mass transfer into an open system?

    The following is what is written in the book I am reading. The energy required to "push" the mass into the system is $$F\delta z=PA\delta z=PV\tag{1}$$ in which ##V## is the molar volume of the closed system, ##F## is the acting force, ##A## is the cross-sectional area, and ##\delta z## is...
  2. Z

    Chemistry How to explain the difference between recompression of ideal gas reversibly and irreversibly after initial irreversible expansion?

    Consider a hydrostatic system in the form of an ideal gas in a container with a movable piston. First let's consider an irreversible isothermal expansion from state a to state b as depicted below We are given ##P_1, V_1, T_a##, and ##P_2##. We can easily compute ##V_2## from the ideal gas...
  3. Z

    Chemistry Calculation of thermodynamic variables for irreversible adiabatic process of ideal gas

    We start at state 1 and end at state 2. We are given the information that $$P_1=1\ \text{bar}$$ $$T_1=300\text{K}$$ $$P_2=0.5\ \text{bar}$$ From the ideal gas law, we can obtain ##V_1##. $$V_1=\frac{nRT_1}{P_1}$$ $$=2494.2\cdot 10^{-5}\mathrm{m^3}$$ My first question arises here. The...
  4. Z

    Chemistry Derivations in adiabatic process for ideal gas with C_V and C_P

    Consider an ideal gas undergoing an adiabatic process. The first law says that $$dU=\delta Q+\delta w=\delta w=-PdV$$ since ##\delta Q=0## for an adiabatic process. ##U## is a function of any two of ##P,V##, and ##T##. Consider ##U_1=U_1(T,V)## and ##U_2=U_2(T,P)##. For an ideal gas we...
  5. cianfa72

    I State equations for a thermodynamic substance/system

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  6. C

    Trouble solving for end state of two control volumes in a rigid tank

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  7. F

    A Average temperature in a greenhouse

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  8. L

    Change of entropy in the Universe in a thermodynamic cycle

    (a) We first find that: ##T_A=\frac{P_A V_A}{nR}=\frac{1\cdot 10^5 \cdot 4}{40\cdot 8.314}K\approx 1202.7904 K##, ##\frac{T_B}{T_A}=\frac{\frac{P_B V_B}{nR}}{\frac{P_A V_A}{nR}}=\frac{P_B V_B}{P_A V_A}=\frac{P_A \frac{V_A}{2}}{P_A V_A}=\frac{1}{2}##, ##\frac{T_C}{T_B}=\frac{P_C...
  9. warhammer

    Question on First Law of Thermodynamics (Paramagnet)

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  10. J

    Finding temperature change, thermodynamics first law

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  11. P

    When do formulas for adiabatic processes apply?

    In this problem, the method used to solve the question is to equate pdV with change in internal energy. This implies an adiabatic process as Q = 0? (not sure about this claim) However, why is it not correct to simply apply the PV^ϒ = constant formula? Thank you.
  12. B

    Engineering Steady flow energy equation in Thermodynamics

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  13. A

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  14. Rahulx084

    Questions about the Point Function (Thermodynamics)

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  15. J

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  16. physics_pi_rate

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  17. T

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  18. K

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  19. Perodamh

    Steady Flow, Thermodynamics First Law

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  20. Clara Chung

    Question about thermodynamics first law

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  21. Likith D

    Heat in Crowded Places: Origin and Explanation

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  22. House

    Understanding the Molar Heat Capacity of an Ideal Gas

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  23. T

    Exhaust velocity of a fire extinguisher

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  24. V

    How to apply the First Law of Thermodynamics to this problem?

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  25. D

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  26. ashash_ash

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  27. A

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  28. D

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  29. K

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  30. B

    Thermodynamics First Law Question

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  31. A

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  32. J

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  33. C

    Thermodynamics First Law Problem

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  34. K

    Problem on thermodynamics first law again

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  35. A

    How Does Heat Affect the Expansion of Monatomic Gas in an Insulated Cylinder?

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