Question

Liquid hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4}\), has been used as a fuel for rockets. When the rocket is to be launched, a catalyst causes the liquid hydrazine to decompose quickly into elemental nitrogen and hydrogen gases. The rapid expansion of the product gases and the heat released by the reaction provide the thrust for the rocket. Write the unbalanced equation for the reaction of hydrazine to produce nitrogen and hydrogen gases.

Short answer

The unbalanced equation for the decomposition reaction of hydrazine is: \[\mathrm{N}_{2}\mathrm{H}_{4} \rightarrow \mathrm{N}_{2} + \mathrm{H}_{2}\] After balancing, the final balanced equation is: \[\mathrm{N}_{2}\mathrm{H}_{4} \rightarrow \mathrm{N}_{2} + 2\mathrm{H}_{2}\]

Step-by-step solution

Identify the reactants and products

The only reactant in this reaction is liquid hydrazine, represented by the chemical formula \(\mathrm{N}_{2}\mathrm{H}_{4}\). When the reaction occurs, the hydrazine decomposes into nitrogen gas and hydrogen gas. Nitrogen gas has the chemical formula \(\mathrm{N}_{2}\), and hydrogen gas has the chemical formula \(\mathrm{H}_{2}\). Step 2: Write the unbalanced equation

Write the unbalanced equation

Now that we have identified the reactants and products, we can write the unbalanced equation for the decomposition reaction of hydrazine: \[\mathrm{N}_{2}\mathrm{H}_{4} \rightarrow \mathrm{N}_{2} + \mathrm{H}_{2}\] This equation is not yet balanced because there are a different number of hydrogen atoms in the reactants and the products. To balance this equation, we will need to adjust the coefficients in front of the reactants and products. Step 3: Balance the equation

Balance the equation

To balance the equation, we will adjust the coefficients to ensure there are the same number of atoms for each element on both sides of the equation. First, we will need to balance the hydrogen atoms: \[\mathrm{N}_{2}\mathrm{H}_{4} \rightarrow \mathrm{N}_{2} + 2\mathrm{H}_{2}\] Now we have 4 hydrogen atoms on both sides of the equation (1 hydrazine molecule contains 4 hydrogen atoms, and 2 hydrogen gas molecules contain 4 hydrogen atoms). Next, we need to balance the nitrogen atoms. In this case, the nitrogen atoms are already balanced with two nitrogen atoms on both sides of the equation. After balancing, the final balanced equation is: \[\mathrm{N}_{2}\mathrm{H}_{4} \rightarrow \mathrm{N}_{2} + 2\mathrm{H}_{2}\]

Key concepts

Decomposition Reaction

A decomposition reaction is a type of chemical reaction in which a compound breaks down into simpler substances. In the case of hydrazine (\(\text{N}_2\text{H}_4\)), it decomposes into nitrogen gas (\(\text{N}_2\)) and hydrogen gas (\(\text{H}_2\)).
This process involves breaking the bonds in the original compound to form new bonds in the products.

• These reactions are generally endothermic, meaning they require energy to proceed.
• However, in rocket applications, the rapid decomposition releases energy, making the reaction seemingly exothermic.
• The decomposition of hydrazine is a key reaction in the aerospace industry because it happens quickly and releases gases at high temperatures, generating thrust.

The simplicity and speed of this reaction make it ideal for use in rocket propulsion.

Balancing Equations

Balancing chemical equations is crucial to obey the law of conservation of mass, which states that matter cannot be created or destroyed.
For the decomposition of hydrazine, the initial unbalanced equation is:\[\text{N}_2\text{H}_4 \rightarrow \text{N}_2 + \text{H}_2\]
In the unbalanced equation, there are 4 hydrogen atoms in hydrazine but only 2 in the hydrogen gas product.
By adjusting the coefficients:\[\text{N}_2\text{H}_4 \rightarrow \text{N}_2 + 2\text{H}_2\]

• Now, both sides have 4 hydrogen atoms, balancing the equation.
• The nitrogen atoms are already balanced with 2 on each side.
• Balancing requires practice, but understanding the process ensures the correct proportions of reactants and products.

This balanced equation accurately reflects the quantities of each substance involved.

Rocket Fuel

Rocket fuel, like hydrazine, is used to propel rockets into space. It must be capable of producing a large amount of thrust quickly.
Hydrazine is a popular choice due to its high-energy decomposition reaction.

• Rocket fuels are often chosen for their high-density energy and ability to release gases that expand rapidly.
• During decomposition, hydrazine releases nitrogen and hydrogen gases, which expand and propel the rocket forward.
• The efficiency of rocket fuel is measured by its specific impulse, a measure of thrust per weight unit of fuel.

This makes hydrazine a highly efficient propellant in space exploration.

Catalyst

A catalyst is a substance that speeds up a chemical reaction without being consumed.
In the hydrazine decomposition, a catalyst initiates the reaction, allowing it to proceed rapidly.

• Catalysts work by lowering the activation energy needed for the reaction, allowing it to occur more easily.
• The presence of a catalyst ensures that hydrazine decomposes quickly when the rocket needs to launch.
• They are critical in various chemical processes, making reactions more efficient and sustainable.

Using a catalyst in rocket fuel applications maximizes thrust by ensuring rapid gas production.

Hydrazine

Hydrazine (\(\text{N}_2\text{H}_4\)) is a colorless liquid used as rocket fuel due to its high-energy properties.
It is valued for its ability to decompose rapidly and energetically.

• Hydrazine is composed of nitrogen and hydrogen, making it relatively simple yet powerful.
• Its decomposition into nitrogen and hydrogen gases is highly exothermic, providing the necessary thrust for rockets.
• While effective, hydrazine is toxic and requires careful handling and storage.

These properties make it an important and potent component in aerospace technology.