Question

If a steel cylinder of hydrogen gas is cooled from \(50{ }^{\circ} \mathrm{C}\) to \(0^{\circ} \mathrm{C},\) does the motion of hydrogen molecules increase or decrease?

Short answer

The motion of hydrogen molecules decreases as the temperature decreases.

Step-by-step solution

Understanding Temperature and Molecular Motion

When the temperature of a gas is decreased, the average kinetic energy of its molecules decreases. Temperature is directly proportional to kinetic energy, which is the energy associated with the motion of molecules.

Applying Temperature Change to Hydrogen Gas

The steel cylinder with hydrogen gas is cooled from \(50{ }^{\circ} \mathrm{C}\) to \(0{ }^{\circ} \mathrm{C}\). This is a decrease in temperature.

Determining the Effect on Molecular Motion

Since the temperature decreases, this means the average kinetic energy of the hydrogen molecules also decreases. As a result, the motion of the hydrogen molecules decreases.

Key concepts

Kinetic Energy

Every object in motion carries kinetic energy. In the context of gases, kinetic energy is directly linked to their temperature. As the temperature of a gas increases, so does the average kinetic energy of its molecules.
The molecules move faster because the added energy excites them, making them zip around more vigorously. Conversely, when the temperature decreases, there is less energy available, and the molecules, therefore, slow down. This relationship is crucial to understanding how gases behave. When a gas, like hydrogen in a steel cylinder, is cooled, its kinetic energy diminishes. This means that on average, each hydrogen molecule carries less energy, reducing their movement.
This reduction in kinetic energy can also influence the pressure and volume of the gas, according to the various gas laws like Boyle's law and Charles's law. Understanding and predicting gases' behaviors depend heavily on the concept of kinetic energy and how it changes with temperature.

Molecular Motion

Gas molecules are in constant random motion, colliding with each other and the walls of their container. These movements are not just chaotic but also represent essential characteristics of gases, as explained by the kinetic molecular theory.
Molecular motion increases with kinetic energy. When you heat a gas, its molecules move more rapidly. This is because they have more energy to convert into motion. On the flip side, if you cool a gas, such as in our case with the steel hydrogen cylinder, the molecules slow down.
The decrease in motion arises because less kinetic energy is available to keep the molecules bouncing energetically. This decrease impacts how gases expand, interact, and transition into other states of matter under various conditions. Understanding molecular motion is critical for predicting how gases will behave in different environments and for applications in physics and chemistry.

Temperature Effects

Temperature plays a pivotal role in the behavior of gases. It is a measure of the average kinetic energy of molecules in a substance. Thus, temperature changes directly affect how gas molecules move and interact.
When we refer to temperature effects on gases, we're talking about how heating or cooling a gas alters its molecular energy and movement. Increasing temperatures give molecules more energy, causing them to move faster. This means if the temperature rises too much, gases can expand or increase in pressure significantly. Conversely, decreasing temperatures reduce molecular energy. For the steel cylinder with hydrogen gas, cooling from 50°C to 0°C causes the hydrogen molecules to lose kinetic energy, slowing their motion.
This slowed motion can cause the gas to contract, reducing gas pressure within the cylinder. Understanding these temperature effects allows us to predict reactions and changes in gases, crucial for both theoretical studies and practical applications in everyday life.