Question

Explain why a helium weather balloon expands as it rises in the air. Assume that the temperature remains constant.

Short answer

The balloon expands because air pressure decreases with altitude, causing its volume to increase.

Step-by-step solution

Understanding the Ideal Gas Law

The behavior of gases can be explained through the Ideal Gas Law, which is given by the equation \( PV = nRT \). Here, \( P \) stands for pressure, \( V \) stands for volume, \( n \) is the number of moles of gas, \( R \) is the universal gas constant, and \( T \) is the temperature in Kelvin.

Analyzing the Conditions as the Balloon Rises

As the balloon rises in the atmosphere, the external air pressure \( P \) decreases. According to our assumption, the temperature \( T \) remains constant. Thus, using the Ideal Gas Law, \( nRT \) is constant, and if \( P \) decreases, \( V \) must increase to keep the equation balanced.

Applying the Concept to the Balloon

For the helium balloon, the decrease in external air pressure allows it to expand because the pressure inside the balloon becomes greater than the pressure outside. As a result, the balloon increases in volume to balance the pressure differences as it rises in the atmosphere.

Key concepts

Helium Weather Balloon

Helium weather balloons are used for various scientific purposes. They help in collecting data about the atmosphere by carrying sensors and instruments. These balloons are filled with helium gas, which is lighter than air. This property allows the balloon to rise as it displaces the heavier air around it. While ascending, the helium balloon travels through different layers of the atmosphere. Each layer varies in pressure and temperature. The ascent of the helium balloon is mostly due to the principles of buoyancy combined with the characteristics of helium. These balloons are essential tools in meteorology and environmental research. They allow us to gather critical data in real time and improve weather forecasting accuracy.

Gas Expansion

The phenomenon of gas expansion is central to understanding the behavior of the helium weather balloon. As the balloon ascends, it moves from an area of higher pressure to one of lower pressure. According to the Ideal Gas Law, when a gas experiences a decrease in pressure, it tends to expand.

• The equation for the Ideal Gas Law is \( PV = nRT \).
• When pressure \( P \) drops, volume \( V \) must increase if temperature \( T \) is constant.

This expansion occurs because the gas molecules inside the balloon have more space to move around as the outside pressure decreases. This is why a helium balloon expands as it rises into the sky. The process is an application of the gas laws, particularly emphasizing the relationship between pressure and volume.

Atmospheric Pressure

Atmospheric pressure is a measure of the force exerted by the air above the surface of the Earth. It decreases as altitude increases. This decrease is vital for the expansion of a helium weather balloon.

• At sea level, atmospheric pressure is highest.
• As altitude increases, atmospheric pressure decreases.

When a helium balloon rises, it encounters lower atmospheric pressure. This is because there is less air above pressing down. As the pressure outside the balloon decreases, the pressure inside the balloon, which remains initially unchanged, causes the balloon to expand. This disparity in pressure is what leads to the physical expansion of the balloon as it ascends.

Temperature Constancy

Temperature constancy plays a significant role in the expansion of gases, including those in a helium weather balloon. When analyzing situations involving gases, assuming a constant temperature simplifies calculations and helps focus on other variables such as pressure and volume.

• Under constant temperature, volume and pressure changes are highlighted.
• According to the Ideal Gas Law, if \( T \) is constant, then volume \( V \) and pressure \( P \) have an inverse relationship.

In a real-world scenario, the temperature might vary, but assuming it stays constant makes it easier to apply the Ideal Gas Law. By maintaining a constant temperature assumption, students can observe how changes in atmospheric pressure directly cause gas expansion, reflecting the practical dynamics of a weather balloon's ascent.