Question

Which of the following pair cannot be used as a Rocket (c) Liquid \(\mathrm{H}_{2}+\) Liquid \(\mathrm{N}_{2}\) Propellant? \(\quad\) (d) Liquid \(\mathrm{O}_{2}+\) Liquid \(\mathrm{N}_{2} \mathrm{H}_{4}\) (a) Liquid \(\mathrm{H}_{2}+\) Liquid \(\mathrm{O}_{2}\) (b) Liquid \(\mathrm{O}_{2}+\) Liquid \(\mathrm{Ar}\)

Short answer

Liquid O2 and Liquid Ar (b) cannot be used as a rocket propellant pair.

Step-by-step solution

Understand Rocket Propellants

Rocket propellants are substances used to produce thrust to propel rockets. Effective rocket propellants include a fuel and an oxidizer. The fuel burns with the oxidizer in a chemical reaction to produce a large volume of gases at high pressure.

Evaluate Each Pair

Let's analyze each pair: (a) Liquid H2 and Liquid O2: Liquid hydrogen (H2) as fuel and liquid oxygen (O2) as the oxidizer are common rocket propellants. (b) Liquid O2 and Liquid Ar: Liquid oxygen is an oxidizer, but argon (Ar) is an inert gas and does not serve as fuel. (c) Liquid H2 and Liquid N2: Both are non-reactive in the sense required for rocket propulsion since N2 is inert. (d) Liquid O2 and Liquid N2H4: Hydrazine (N2H4) is a reliable rocket fuel with liquid O2 as the oxidizer.

Conclusion - Infeasible Pair

Among the given pairings, (c) Liquid H2 and Liquid N2, and (b) Liquid O2 and Liquid Ar cannot be used for rocket propulsion. Both pairs lack an explosive combination because either the oxidizer or the fuel component is non-reactive for energy release.

Identify the Correct Non-Feasible Pair

The most directly accurate answer based on typical understanding is (b) Liquid O2 and Liquid Ar, because it cannot combust as argon is inert and provides no energy as a fuel. Liquid H2 and N2 (c) are theoretically reactable, but N2 usually undergoes a reaction to dissociate at very high temperatures, which isn’t typical for propellant use.

Key concepts

Oxidizer and Fuel Combination

A successful rocket propulsion system relies on the effective combination of an oxidizer and a fuel. Together, these two components undergo a chemical reaction that generates the thrust needed to propel a rocket.
Fuel is the substance that can combust, while the oxidizer provides the necessary oxygen for the fuel to burn, especially in the vacuum of space where oxygen is not abundantly present.

• For a system to work efficiently, the oxidizer and fuel must create a high-energy output with strong gas expansion capabilities.
• Common examples of effective rocket propellant combinations include liquid hydrogen ( H_2 ) as fuel and liquid oxygen ( O_2 ) as the oxidizer. This combination is famous for its high efficiency and power.
• Another effective combo is liquid O _2 and hydrazine ( N_2 H_4 ), where hydrazine acts as a powerful fuel.

The ideal choice hinges on creating a product that is capable of bringing about extensive gas expansion when combusted, ensuring strong thrust generation.

Inert Gases in Propulsion

In the world of rocket propulsion, inert gases play a rather different and often more limited role compared to typical fuel and oxidizer pairings. Inert gases are those that do not easily react with other substances.
Because they are stable and not reactive, they do not produce thrust when combined with an oxidizer or another potential fuel.

• An excellent example is argon ( Ar ), which is an inert gas. When combined with liquid oxygen ( O_2 ), as mentioned in the original exercise, it does not undergo any exothermic reaction, thus it cannot propel a rocket.
• Similarly, nitrogen ( N_2 ) in its liquid form does not provide the energy output necessary for propulsion when paired with liquid hydrogen ( H_2 ).

While inert gases might be useful in other contexts, such as pressurizing fuel tanks or cooling processes, they do not directly contribute to the propulsion of rockets.

Chemical Reaction for Thrust

At the heart of rocket propulsion is a powerful chemical reaction that generates thrust. This reaction is crucial as it transforms the stored energy within the chemical bonds of the fuel and oxidizer into kinetic energy that propels the rocket.
The basic principle involves the burning of the fuel in the presence of an oxidizer, which forms a high-pressure and high-temperature gas

• This gas expands rapidly and is forced through the rocket nozzle, generating a reaction force that pushes the rocket forward.
• Efficient pairs like liquid hydrogen ( H_2 ) and liquid oxygen ( O_2 ) illustrate this process perfectly, providing a high thrust-to-weight ratio, essential for escaping Earth's gravity.
• The successful reaction requires precise balancing of the oxidizer and fuel to maintain the desired combustion stability.

Without a vigorous and well-controlled chemical reaction, a rocket fails to achieve lift-off, underscoring the critical importance of this process in the realm of space exploration.