Question

Hydrazine \(\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)\) and dinitrogen tetroxide \(\left(\mathrm{N}_{2} \mathrm{O}_{4}\right)\) form a self-igniting mixture that has been used as a rocket propellant. The reaction products are \(\mathrm{N}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) . (a) Write a balanced chemical equation for this reaction. (b) What is being oxidized, and what is being reduced? (c) Which substance serves as the reducing agent and which as the oxidizing agent?

Short answer

The balanced chemical equation for the reaction is \[\text{2 N}_{2}\text{H}_{4}+\text{N}_{2}\text{O}_{4}\rightarrow\text{3 N}_{2}+\text{8 H}_{2}\text{O} \]. In this reaction, N2H4 is being oxidized (oxidation state goes from -2 to 0) and is the reducing agent, while N2O4 is being reduced (oxidation state goes from +4 to 0) and serves as the oxidizing agent.

Step-by-step solution

(a) Write a balanced chemical equation

First, let us list the reactants and products of the given reaction: Reactants: Hydrazine (N2H4) and dinitrogen tetroxide (N2O4) Products: Nitrogen gas (N2) and water (H2O) Now, we have to write the balanced chemical equation. Start by writing the reactants and products like shown: N2H4 + N2O4 -> N2 + H2O To balance the equation, we need to ensure that the number of atoms for each element is equal on both sides of the equation: 1. Balance the nitrogen atoms: 2 N2H4 + N2O4 -> 3 N2 + H2O 2. Balance the hydrogen atoms: 2 N2H4 + N2O4 -> 3 N2 + 8 H2O The balanced chemical equation is: \[\text{2 N}_{2}\text{H}_{4}+\text{N}_{2}\text{O}_{4}\rightarrow\text{3 N}_{2}+\text{8 H}_{2}\text{O} \]

(b) Identify the oxidation and reduction processes

Oxidation involves the loss of electrons whereas reduction involves the gain of electrons. To find out what is being oxidized and what is being reduced, we have to determine the oxidation states of each element in both reactants and products: N in N2H4: -2 (due to the more electronegative H) N in N2O4: +4 (due to the more electronegative O) N in N2: 0 H in H2O: +1 O in H2O: -2 Now, compare the oxidation states before and after the reaction: 1. Nitrogen in N2H4 goes from -2 to 0. This is an increase in the oxidation state, so N2H4 is being oxidized. 2. Nitrogen in N2O4 goes from +4 to 0. This is a decrease in the oxidation state, so N2O4 is being reduced.

(c) Identify the reducing and oxidizing agents

The substance that causes the reduction of another substance (by losing electrons) is called the reducing agent. In contrast, the substance that causes the oxidation of another substance (by gaining electrons) is called the oxidizing agent. In this reaction: 1. N2H4 is being oxidized, so it is the reducing agent. 2. N2O4 is being reduced, so it is the oxidizing agent.

Key concepts

Balanced Chemical Equation

Understanding a balanced chemical equation is a fundamental skill in chemistry. Just like in our example with rocket propellants, balancing a reaction involves ensuring that the number of atoms for each element is the same on both sides of the equation. This represents the conservation of mass, indicating that atoms are neither created nor destroyed in a chemical reaction.

Let's take a closer look at how to balance the equation step by step. Start with a list of all reactants and products. Then, write out the unbalanced chemical equation. Next, using coefficients, adjust the number of molecules to ensure that for every element, the atom count is the same on each side.

For instance, the propellant example required balancing nitrogen and hydrogen atoms. The final equation, \[\text{2 N}_{2}\text{H}_{4}+\text{N}_{2}\text{O}_{4}\rightarrow\text{3 N}_{2}+\text{8 H}_{2}\text{O} \], shows that we have equal numbers of nitrogen (seven on each side) and hydrogen (eight on each side) atoms, which is key to a correctly balanced equation.

Oxidation and Reduction

Oxidation and reduction are two halves of the same reaction, always occurring together during a process called redox. Oxidation refers to the loss of electrons, while reduction is all about the gain of electrons. To determine which occurs in a given reaction, you'll need to assign oxidation states to each element both before and after the reaction.

In the rocket propellant equation, nitrogen's oxidation state changes, which clues us into what's oxidized and what's reduced. Remember, a more positive oxidation state means oxidation, and a more negative means reduction. For the propellant reaction, hydrazine's nitrogen goes from an oxidation state of -2 to 0, signifying oxidation. Conversely, dinitrogen tetroxide's nitrogen goes from +4 to 0, signifying reduction.

Reducing and Oxidizing Agents

Identifying the reducing and oxidizing agents is a crucial step because these agents are what drive the chemical reaction forward. The reducing agent is the 'giver,' it loses electrons and itself gets oxidized. On the flip side, the oxidizing agent is the 'taker,' it gains electrons and gets reduced.

In our rocket fuel example, we determined that hydrazine, \(\text{N}_{2}\text{H}_{4}\), becomes oxidized; therefore, it serves as the reducing agent. Meanwhile, dinitrogen tetroxide, \(\text{N}_{2}\text{O}_{4}\), gets reduced and thus acts as the oxidizing agent. Understanding the role each substance plays in a redox reaction is vital as it helps to unravel how and why certain substances interact chemically.