Heat and Thermodynamics 6 Question 5
9. Two moles of ideal helium gas are in a rubber balloon at $30^{\circ} C$. The balloon is fully expandable and can be assumed to require no energy in its expansion. The temperature of the gas in the balloon is slowly changed to $35^{\circ} C$. The amount of heat required in raising the temperature is nearly (take $R=8.31 J / mol-K)$
(a) $62 J$
(b) $104 J$
(c) $124 J$
(d) $208 J$
(2012)
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Answer:
Correct Answer: 9. (d)
Solution:
- The process may be assumed to be isobaric.
$$ \begin{aligned} \therefore \quad Q & =n C _p \Delta T=(2)\left(\frac{5}{2} R\right)(5) \\ & =5 \times 8.31 \times 5=207.75 J \approx 208 J \end{aligned} $$
