Question

On heating 128 g of oxygen gas from 0${}^{\circ }$C to 100${}^{\circ }$C, $C_V$ and $C_P$ on an average are 5 and 7 cal mol${}^{-1}$ degree${}^{-1}$, the value of $\Delta$U and $\Delta$H are respectively :

• A. 2800 cal, 2000 cal
• B. 2000 cal, 2800 cal
• C. 280 cal, 200 cal
• D. none of the above

Answer 1

Answer: (B)

2000 cal, 2800 cal

128 g of oxygen (molecular weight = 32) corresponds to 4 moles.

The enthalpy change is $\Delta H=n{C}_P\Delta T=4\times 7\times 100=2800$ cal.

The change in internal energy is $\Delta U=n{C}_V\Delta T=4\times 5\times 100=2000$ cal.