Problem 86 - A Complete Resource Book in Chemistry for JEE Main

Question

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

Step-by-Step Solution

Answer

Option (b) Liquid \\( \mathrm{O}_{2}\\ ) + Liquid \\( \mathrm{Ar}\\ ) cannot be used as a rocket propellant.

Step 1: Identify oxidizers and fuels

A rocket propellant system generally consists of a fuel and an oxidizer. Oxygen (\(\mathrm{O}_2\)) is a commonly used oxidizer while hydrogen (\(\mathrm{H}_2\)) is a frequently used fuel. The goal is to identify which combinations in the options can function as a typical fuel-oxidizer pair.

Step 2: Evaluate each option

- (a) Liquid \(\mathrm{H}_{2}\) + Liquid \(\mathrm{O}_{2}\): Liquid hydrogen is a fuel and liquid oxygen is an oxidizer, making them a feasible propellant pair.- (b) Liquid \(\mathrm{O}_{2}\) + Liquid \(\mathrm{Ar}\): Liquid oxygen can be an oxidizer, but argon is an inert gas and cannot act as a fuel.- (c) Liquid \(\mathrm{H}_{2}\) + Liquid \(\mathrm{N}_{2}\): While nitrogen is not a typical oxidizer, hydrogen remains a possible fuel.- (d) Liquid \(\mathrm{O}_{2}^{2}\) + Liquid \(\mathrm{N}_{2}H_{4}\): Dinitrogen tetroxide can act as an oxidizer and hydrazine (\(\mathrm{N}_{2}H_{4}\)) can be used as a fuel.

Step 3: Identify the incorrect pair

Based on evaluation, option (b) Liquid \(\mathrm{O}_{2}\) + Liquid \(\mathrm{Ar}\) is not a feasible rocket propellant pair because argon cannot serve as a fuel or an oxidizer.

Key Concepts

Oxidizers and Fuels

In rocket propulsion, the combination of an oxidizer and a fuel is instrumental. The primary role of an oxidizer is to provide oxygen that allows the fuel to combust, even in the oxygen-deprived environment of space. This combustion is what generates the thrust necessary to launch a rocket. Typically:

• Oxidizers: Substances that donate oxygen, supporting the burning of fuel. Common examples include liquid oxygen (\(\mathrm{O}_2\)) and dinitrogen tetroxide (\(\mathrm{N}_2\mathrm{O}_4\)).
• Fuels: Substances that burn when combined with oxidizers. Popular choices include liquid hydrogen (\(\mathrm{H}_2\)) and kerosene.

This combination is vital for producing the force required to propel rockets away from Earth's gravity and into space. The oxidizer-fuel pair must be chosen carefully to ensure safety and efficiency in the propulsion system. For example, liquid hydrogen and liquid oxygen form a well-tested and efficient pair, delivering high energy with relatively low environmental impact.

Liquid Hydrogen

Liquid hydrogen is a highly efficient rocket fuel favored for its energy-rich properties and lightweight nature. As a cryogenic fuel, liquid hydrogen is stored at extremely cold temperatures, below -423°F (-253°C), which makes it challenging to handle but highly effective in propulsion. Some key features of liquid hydrogen include:

• High energy output: Produces immense energy when the hydrogen molecules combine with oxygen.
• Low molecular weight: Contributes to its efficiency and performance as a propellant.
• Clean burn: The primary combustion product is water, making it an environmentally friendly option.

Despite these benefits, liquid hydrogen requires special storage and transportation systems to handle its extreme cold. These challenges, however, are outweighed by its excellent energy performance, making it a staple in modern space missions like those carried out by NASA.

Liquid Oxygen

Liquid oxygen is a common choice as an oxidizer in rocket propellants due to its ability to release a substantial amount of oxygen when transitioning from liquid to gas. This property supports the combustion of the fuel, producing the thrust necessary for rocket propulsion. Key aspects of liquid oxygen include:

• High oxygen content: Ensures an efficient combustion process.
• Combines readily with various fuels: Pairs effectively with liquid hydrogen, kerosene, and more.
• Ease of production and storage: Oxygen is abundant in the atmosphere, making it relatively easy to produce and store in its liquid state at conditions below -297°F (-183°C).

Liquid oxygen is widely used in aerospace technologies, contributing to the effective functioning of many rockets due to its strong oxidizing properties. It is favored not only for its performance but also for its availability and straightforward handling.

Inert Gases in Rocketry

Inert gases, like argon, are chemically non-reactive under normal conditions, meaning they do not easily form chemical compounds or react with other substances. In the context of rocketry, their properties make them unsuitable as fuel or oxidizers. Here's why inert gases are not used in propulsion:

• Non-reactivity: They do not combust or release energy necessary for propulsion.
• Lack of oxidizing or fueling capabilities: They cannot supply oxygen for combustion nor act as a combustible material.
• Used in other roles: While not used as propellants, inert gases can serve other purposes, such as pressurizing fuel tanks or providing non-reactive environments for specific components.

Inert gases can be beneficial in various supportive capacities within aerospace applications, but they are not suited for providing the thrust needed in rocket launches.