Question

Which one of the following equations does not correctly represent the first law of thermodynamics for the given process ?

• A. Isothermal process : q = – w
• B. Cyclic process : q = – w
• C. Adiabatic process :$\Delta$E = q
• D. Expansion of a gas into vacuum :$\Delta$E = q

Answer 1

Answer: (C)

Adiabatic process :$\Delta$E = q

Answer 2

According to 1st law of thermodynamics,

$\Delta$E = q + w.

For isothermal process, $\Delta$E = 0. Hence, q = – w

For cyclic process, $\Delta$E= 0 Hence,

For expansion into vacuum, w = 0. hence $\Delta$E = q.