Question 844: Thermodynamics & KTG

Question

For a monoatomic gas, the work done at constant pressure is '$$\mathrm{W}$$' The heat supplied at constant volume for the same rise in temperature of the gas is
$$[\gamma=\frac{C_p}{C_v}=\frac{5}{2}$$ for monoatomic gas]

Accepted Answer

To determine the heat supplied at constant volume for a monoatomic gas, let's start by defining some fundamental relationships and properties of monoatomic gases.
The ratio of specific heats $$\gamma$$ for a monoatomic gas is given as:
$$\gamma = \frac{C_p}{C_v} = \frac{5}{3}$$
Where:
$$C_p$$: Specific heat at constant pressure
$$C_v$$: Specific heat at constant volume
The work done at constant pressure, $$\mathrm{W}$$, for a rise in temperature $$\Delta T$$ is defined as:
$$W = P \Delta V$$
Using the ideal gas law, $$PV = nRT$$, we know that at constant pressure, $$V \propto T$$, so:
$$P \Delta V = n R \Delta T$$
Thus, the work done at constant pressure can be written as:
$$W = n R \Delta T$$
The heat supplied at constant pressure $$Q_p$$ is given by:
$$Q_p = n C_p \Delta T$$
Since the work done, $$W$$, at constant pressure is equivalent to $$n R \Delta T$$, it can also be related to $$Q_p$$ using the specific heat at constant pressure:
$$Q_p = W \cdot \frac{C_p}{R}$$
The specific heat at constant volume, $$Q_v$$, is given by:
$$Q_v = n C_v \Delta T$$
Since $$C_p / C_v = \gamma$$:
$$C_p = \gamma C_v$$
Therefore, we can substitute to get:
$$C_v = \frac{C_p}{\gamma}$$
Substitute $$C_v$$ into the expression for the heat supplied at constant volume:
$$Q_v = n \left(\frac{C_p}{\gamma}\right) \Delta T$$
Since $$n R \Delta T = W$$, and using the relationship between $$C_p$$ and $$R$$ for a monoatomic gas:
$$C_p = \frac{\gamma R}{\gamma - 1}$$
For a monoatomic gas, $$\gamma = \frac{5}{3}$$:
$$C_p = \frac{\frac{5}{3} R}{\frac{5}{3} - 1} = \frac{\frac{5}{3} R}{\frac{2}{3}} = \frac{5}{2} R$$
Therefore, $$C_v$$ is:
$$C_v = \frac{C_p}{\gamma} = \frac{\frac{5}{2} R}{\frac{5}{3}} = \frac{3R}{2}$$
Thus:
$$Q_v = n C_v \Delta T = n \frac{3R}{2} \Delta T$$
Since $$W = n R \Delta T$$, we can write:
$$Q_v = \frac{3}{2} \cdot W$$
Hence, the heat supplied at constant volume for the same rise in temperature of the gas is:
Option D: $$\frac{3 W}{2}$$

Answer

$$2 \mathrm{~W}$$

Answer

$$\mathrm{W}$$

Answer

$$\frac{W}{2}$$

Answer

$$\frac{3 W}{2}$$

Thermodynamics & KTG

For a monoatomic gas, the work done at constant pressure is '$\mathrm{W}' The heat supplied at constant volume for the same rise in temperature of the gas is [\gamma=\frac{C_p}{C_v}=\frac{5}{2}$ for monoatomic gas]

Choose the correct answer: