Question

Find the change in internal energy in joule. When 10g of air is heated from ${30}^{\circ }$ to ${40}^{\circ }$ (Cv$=$ 0.172 kcal/kg K, J$=$4200 J/kcal)

• A. 62.24 J
• B. 72.24 J
• C. 52.24 J
• D. 82.24 J

Answer 1

The correct option is B 72.24 J

Given:

Mass of air , m=10g =10$+{10}^{-3}Kg={10}^{-2}Kg$

$C_v=0.172Kcal/KgK=0.172\times 4200J/KgK$

Initial temperature, $T_i=30°C=(30+273)K=303K$

Final temperature, $T_f=40°C=(40+273)K=313K$

Solution:

Change in temperature= 313-303 K =10K

Change in internal energy= m$C_v\delta T$

$\Rightarrow \delta U={10}^{-2}\times 0.172\times 4200\times 10$

$\Rightarrow \delta U=72.24J$

Hence, option B is correct.