Question

$0.64\text{g}$ of oxygen is kept in a rigid container and is heated. Find the amount of heat needed to raise the temperature from ${25}^{\circ }\text{C}$ to ${35}^{\circ }\text{C}$. The molar heat capacity of oxygen at constant volume is $20{\text{J K}}^{-1}{\text{mol}}^{-1}$.

• A. $2\text{J}$
• B. $1\text{J}$
• C. $4\text{J}$
• D. $8\text{J}$

Answer 1

The correct option is C $4\text{J}$

The molecular weight of oxygen $M=32\text{g/mol}$
number of moles of the gas,
$n=\frac{0.64\text{g}}{32{\text{g.mol}}^{-1}}=0.02\text{mol}$
$\Delta T=35-25={10}^{\circ }C=10K$
since difference of temperature in celcius and kelvin yields same result.
$\Rightarrow$The amount of heat $\left(Q\right)$ is required at constant volume (because container's volume is fixed).
$\Rightarrow Q=n{C}_V\Delta T$
$Q=0.02\text{mol}\times 20{\text{JK}}^{-1}{\text{mol}}^{-1}\times 10\text{K}$
$\therefore Q=4\text{J}$