Question

Will a balloon filled with the given gas rise in the air or drop to the ground? (Assume the mass of the balloon is negligible and the density of air is \(1.29 \mathrm{~g} / \mathrm{L} .)\) (a) helium \((d=0.178 \mathrm{~g} / \mathrm{L})\) (b) argon \((d=1.78 \mathrm{~g} / \mathrm{L})\)

Short answer

(a) helium will rise, (b) argon will fall.

Step-by-step solution

Understand the Concept

To determine whether a balloon will rise or fall, compare the density of the gas inside the balloon with the density of air. A balloon will rise if the gas inside is less dense than the surrounding air. Conversely, it will fall if the gas is denser.

Analyze Helium

For helium with a density of \(0.178 \text{ g/L}\), compare it to the density of air, which is \(1.29 \text{ g/L}\). Since \(0.178 \text{ g/L}\) is less than \(1.29 \text{ g/L}\), a helium-filled balloon will rise.

Analyze Argon

For argon with a density of \(1.78 \text{ g/L}\), compare it to the density of air, \(1.29 \text{ g/L}\). Since \(1.78 \text{ g/L}\) is greater than \(1.29 \text{ g/L}\), an argon-filled balloon will fall.

Key concepts

Helium

Helium is a light and non-reactive gas that is well known for its lifting properties. Because helium's density is much lower than air, it makes balloons float upward.
Helium's density is only 0.178 g/L, which is significantly less than the density of air, 1.29 g/L.
This difference is crucial because it allows helium to provide the buoyancy needed to lift a balloon into the sky.

• Used in party balloons
• Non-flammable and safe for handling
• Provides a classic example of a noble gas

When you fill a balloon with helium, the lower density of the helium compared to surrounding air means that the weight of the displaced air (which is greater than the balloon and helium combined) creates an upward force.
That's the simple reason why helium balloons rise.

Argon

Argon is another noble gas like helium, but it is much denser. With a density of 1.78 g/L, argon is denser than air.
When a balloon is filled with argon, it does not have the buoyancy to rise; instead, it is likely to fall to the ground.
This gas is often used in environments where non-reactivity is critical, such as in gas-insulated windows or welding.

• Denser than air
• Non-reactive and inert
• Heavier than commonly assumed

Although argon shares noble gas status with helium, its physical properties are significantly different.
Understanding these differences is important when it comes to applications, especially those involving buoyancy.

Buoyancy

Buoyancy is the force that causes objects to float, and it plays a key role in whether a balloon filled with gas will rise or fall.
It is determined by the density difference between the object and the surrounding fluid, which in this case is air.
Think of buoyancy like an invisible hand that can either lift up a balloon or let it drop, depending on how heavy or light the gas inside it is compared to air. The principle of buoyancy is based on Archimedes' principle, which states that the upward buoyant force is equal to the weight of the displaced fluid.
For helium balloons, the displaced air weighs more than the helium-filled balloon, hence they rise.
In contrast, for an argon balloon, the displaced air is lighter than the gas and balloon, making it fall.

• Involves comparison of densities
• Rises when gas inside the balloon is lighter than air
• Falls when gas is denser than air

Understanding buoyancy can help explain many phenomena in everyday life, from why ice floats in water to how massive ships can float in the ocean.