Two scientists discuss why the pressure of a sample of nitrogen gas (N_2) inside a rigid, … — ACT

Two scientists discuss why the pressure of a sample of nitrogen gas ( $N_2$ ) inside a rigid, sealed container increases when the gas is heated from $20^\circ\text{C}$ to $200^\circ\text{C}$ .

Scientist 1
The increase in pressure is due entirely to the increase in the average kinetic energy of the $N_2$ molecules. As the temperature rises, the molecules move faster, colliding with the container walls more frequently and with greater force. The total number of gas molecules remains constant.

Scientist 2
The increase in pressure is due to the thermal dissociation of $N_2$ molecules into individual nitrogen atoms ( $N_2 \rightarrow 2N$ ). As the temperature rises, more molecules split, which increases the total number of gas particles in the container. The average kinetic energy of the particles remains constant.

Which of the following experiments would best determine which scientist's viewpoint is correct?

Heating a sample of helium ( $He$ ), a monatomic gas that cannot thermally dissociate, in a rigid, sealed container and measuring whether the pressure increases.Answer
B
Measuring the total mass of the sealed container of nitrogen gas ( $N_2$ ) before and after heating it from $20^\circ\text{C}$ to $200^\circ\text{C}$ .
C
Adding additional nitrogen gas ( $N_2$ ) to the container at a constant temperature of $20^\circ\text{C}$ and measuring the pressure change.
D
Heating the nitrogen gas ( $N_2$ ) in a container with a flexible volume that maintains constant pressure, and measuring the change in volume.

Answer

Heating a sample of helium, a monatomic gas that cannot thermally dissociate, in a rigid, sealed container and measuring whether the pressure increases.

The correct answer is the experiment using helium gas. Since helium is monatomic and cannot dissociate, any pressure increase observed upon heating must be due to the increased kinetic energy of the atoms, supporting the first viewpoint and disproving the second viewpoint.

Step-by-Step Solution

Identify the key difference between the mechanisms proposed by the two scientists.

Scientist 1 attributes pressure increase to increased molecular speed/kinetic energy, keeping the number of particles constant. Scientist 2 attributes it to an increased number of particles via thermal dissociation, keeping the kinetic energy constant.

To resolve the conflict, an experiment must isolate these two variables (number of particles vs. kinetic energy of particles).

Evaluate the proposed experiment using helium gas.

Helium is monatomic (

He

) and cannot dissociate into smaller particles, meaning the number of particles is forced to remain constant regardless of temperature.

If the pressure of heated helium still increases, it proves that temperature increases pressure without requiring dissociation, thereby supporting the first scientist and refuting the second scientist.

Determine why the other experimental setups fail to resolve the conflict.

Measuring mass does not track particle division (mass is conserved). Adding gas at constant temperature does not test temperature effects. Measuring volume expansion in a flexible container does not distinguish between the two mechanisms because both would cause expansion.

A valid resolving experiment must produce different, clear outcomes for each hypothesis, which the other options fail to do.

Key Concept

Suggesting Experiments to Resolve Viewpoints

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Step-by-Step Solution

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