Question

A liquid when kept inside a thermally insulated closed vessel at 25°C was mechanically stirred from outside. What will be the correct option for the following thermodynamic parameters ?

• A. $\Delta U > 0, q = 0, w > 0$
• B. $\Delta U = 0, q = 0, w = 0$
• C. $\Delta U < 0, q = 0, w > 0$
• D. $\Delta U = 0, q<0, w > 0$

Answer 1

Answer: (A)

(1) $\Delta U > 0,\, q = 0,\, w > 0$

Answer 2

Since the container is thermally insulated, no heat is exchanged, so

$$q = 0.$$

Mechanical stirring does work on the liquid, increasing its internal energy, hence

$$w > 0 \quad \text{and} \quad \Delta U > 0.$$