Question

What amount of heat must be supplied to $35\, g$ of oxygen at room temperature to raise its temperature by $80\,{}^°C$ at constant volume (molecular mass of oxygen is $32$ and $R = 8.3 \,J \,mol^{-1}\, k^{-1}$)

• A. $1.52\, kJ$
• B. $3.23\, kJ$
• C. $1.81\, kJ$
• D. $1.62\, kJ$

Answer 1

Answer: (C)

Here mass of oxygen $(m) = 35\, g,$
molar mass of $O_2 (M) = 32\, g \,mol^{-1}$
rise in temperature, $ΔT = 80\,{}^°C$
$\therefore $ number of moles $n=\frac{m}{M}=\frac{35}{32}=1.09\,mol$
As oxygen is a diatomic gas, then molar specific heat at constant volume is $C_{V}=\frac{5}{2}R$
and amount of heat supplied to gas
$ΔQ = nC_{V}ΔT
=1.09\times\frac{5}{2}R ×80=1.09 × \frac{5}{2} × 8.3 × 80 $
$=1809.4\,J=1.8094\, kJ 1.81 \simeq 1.81\, kJ$