Which of the following equations does not correctly represent the first law of thermodynamcis?

Options

A. Expanison of a gas into vacuum : `Delta U = q`
B. Adiabatic process : `Delta U = - w`
C. Isochoric process : `Delta U = q`
D. Isothermal process : `q = - w`

Answer

B

Explanation

According to the first law of thermodynamics,
`Delta U = q + w`
Fror adiabatic process, `q = 0`. Thus, `Delta U = w`
For expansion into vacuum `(P_(ext) = 0), w = - P Delta V = 0`. Thus,
`Delta U = q`
For isochoric process `(Delta V = 0), Ww = - P Delta V = 0`. Thus, `Delta U = q`
For cyclic process `(U_(f) = U_(i)), Delta U = 0` Thus, `Delta U = q`.
For isothermal process `(Delta T = 0)` involving an ideal gas,
`Delta U = U_(f) - U_(i)`