Question

Which of the following could act as a propellant for rockets? (a) Liquid hydrogen \(+\) liquid nitrogen (b) Lliquid nitrogen + liquid oxygen (c) Liquid hydrogen \(+\) liquid oxygen (d) Liquid oxygen + liquid argon

Short answer

Option (c) liquid hydrogen + liquid oxygen is the suitable propellant.

Step-by-step solution

Define Propellant Criteria

A propellant must be a combination of fuel and oxidizer that can undergo a chemical reaction to produce thrust. The oxidizer accepts electrons from the fuel, enabling combustion in space where there is no air.

Analyze Each Option

Each option must be evaluated to see if it consists of a fuel (providing energy through combustion) and an oxidizer (supporting combustion). A common example is liquid hydrogen as fuel and liquid oxygen as an oxidizer.

Evaluate Option (a)

Liquid hydrogen can act as a fuel, but liquid nitrogen is inert, which means it doesn't support combustion. Hence, this combination is not a suitable propellant.

Evaluate Option (b)

Liquid nitrogen and liquid oxygen are both oxidizers, but there's no fuel in this combination. Therefore, it can't act as a propellant.

Evaluate Option (c)

Liquid hydrogen is a fuel and liquid oxygen is an oxidizer; this combination is commonly used as rocket fuel due to its efficient combustion properties. Thus, this is a valid propellant.

Evaluate Option (d)

Liquid oxygen is an oxidizer, but liquid argon is inert and does not support or undergo combustion, so this combination is not suitable for a propellant.

Conclusion

Considering the fuel and oxidizer roles, option (c) is the only combination where the constituents can undergo a combustion reaction to act as a rocket propellant.

Key concepts

Chemical Reaction

In the context of rocket propulsion, a chemical reaction is fundamental. This reaction occurs when fuel and oxidizer are mixed and burned. Unlike reactions in everyday situations where air might support combustion, rockets often use internal components to produce necessary thrust.
For a reaction to even start, oxygen is typically needed. However, in space, there's no oxygen available. This is why rockets carry their own oxidizers. When the fuel and oxidizer meet, a rapid combustion reaction happens.
As a result, gases expand and eject through the rocket nozzle, thrusting the rocket forward. Imagine it like a balloon releasing air to fly across a room. The faster the gases are expelled, the more thrust is generated.
Having this internal chemical dance is key in launching rockets beyond Earth's atmosphere. It's the powerhouse that combats gravitational pull and guides journeys through the stars.

Fuel and Oxidizer

Fuel and oxidizer are essential components of rocket propellants. The fuel is any substance capable of burning and releasing energy. In more familiar settings, an example is gasoline in cars. For rockets, however, liquid hydrogen is a popular choice.
The oxidizer's role is to provide the necessary oxygen. This facilitates the combustion that fuels the rocket. Liquid oxygen, often paired with liquid hydrogen, serves this purpose splendidly.
Together, they create a high-speed reaction. The burning of this fuel-oxidizer mix produces enormous energy, transforming it into thrust.
In selecting a rocket propellant, it's crucial that the fuel and oxidizer are compatible. They must be able to react energetically and sustain combustion, ultimately acting as the lifeline of the rocket's journey.

Combustion in Space

Combustion in space works differently than on Earth due to the absence of atmospheric oxygen. Rockets can't rely on external sources to ignite their engines.
For space travel, the combustion process needs internal oxygen. That's why oxidizers are so vital. They provide the oxygen necessary for burning the fuel, creating the thrust needed to move the rocket.
When the fuel-oxidizer mix ignites, it produces hot gases that expand rapidly in the rocket's combustion chamber. These gases shoot out of the nozzle with tremendous force, generating propulsion.
Unlike combustion on Earth, this process can be more controlled and efficient. In space exploration, mastering this internal combustion lets rockets travel vast distances beyond the atmosphere they once left behind.