Question

The specific heat of air at constant volume is $0.172 \,Cal \, g^{-1}\,{}^{\circ} C ^{-1}$. The change in internal energy when $5\, g$ of air is heated from $0 ^{\circ} C$ to $4 ^{\circ} C$ at constant volume is

• A. $28.8 \,J$
• B. $14.4 \,J$
• C. $7.2 \,J$
• D. $3.51 \,J$

Answer 1

Answer: (B)

Given: Specific heat of air $=0172 Cal / gC$
Mass of air $=5 g$
Initial temperature $=0 C$
Final temperature $=4 C$
Solution: At constant volume the change in internal energy is given by,
$\Delta U = mC _{ p } \triangle T$
As, $\triangle T =4-0=4 C$
Substituting the values we get,
$\Delta U =3.44 Cal$
Also, $1 Cal =4.2 J$
$\therefore \triangle U =4.2 J \times 3.44=14.188 J \sim 14.4 J$