Question

The reaction of hydrogen and nitrogen gases produces \(5.00 \mathrm{~g}\) of ammonia and releases 3250 cal of heat. How much energy is required to decompose \(5.00 \mathrm{~g}\) of ammonia into hydrogen and nitrogen gases?

Short answer

3250 cal of energy is required to decompose 5.00 g of ammonia.

Step-by-step solution

Understanding the Reaction

The reaction of hydrogen and nitrogen gases to form ammonia can be represented by the balanced chemical equation: \[ N_2(g) + 3H_2(g) \rightarrow 2NH_3(g) \]. This reaction releases energy, given as 3250 cal for 5.00 g of ammonia.

Identifying Energy Release in Forward Reaction

The amount of heat released (exothermic reaction) during the formation of 5.00 g of ammonia is 3250 cal. This means that when this amount of ammonia is formed, 3250 cal of energy is released to the surroundings.

Understanding Energy Requirement for Decomposition

To decompose ammonia back into its constituent gases, hydrogen and nitrogen, the same amount of energy that was released during formation must be absorbed (endothermic process). This is because breaking the bonds requires input of energy equal to that released when the bonds were formed.

Calculating Energy Required for Decomposition

Since 3250 cal of heat was released during the formation, the exact opposite amount, 3250 cal, is needed to decompose the ammonia. Thus, 3250 cal of energy is required to break down 5.00 g of ammonia into hydrogen and nitrogen gases.

Key concepts

Exothermic Reaction

In the world of chemistry, an exothermic reaction is one that releases energy in the form of heat to its surroundings. This process is like a warm hug on a cold day—it gives off heat, warming up everything around it.
One of the most common examples of an exothermic reaction is the formation of ammonia from hydrogen and nitrogen gases. In this case, as the two reactants combine to form ammonia, a notable amount of heat, specifically 3250 calories, is released.
It's crucial to remember that:

• In exothermic reactions, the energy of the products is lower than the energy of the reactants.
• These reactions often result in an increase in temperature of the surroundings.
• Energy released is usually a sign that a reaction is exothermic.

Understanding exothermic reactions helps us predict how systems will behave. For instance, in our exercise, the reaction that forms ammonia releases heat, warming up the space around. This is a key characteristic of exothermic reactions.

Endothermic Process

An endothermic process, unlike an exothermic reaction, absorbs energy rather than releasing it. This can be thought of as the reaction "eating up" energy from its surroundings, making the nearby environment cooler.
These processes take place when more energy is needed to break bonds in the reactants than is released when new bonds are formed in the products.
Let's examine the decomposition of ammonia. For ammonia to decompose back into hydrogen and nitrogen gases, energy must be absorbed. Since 3250 calories were released during the formation of ammonia, the same amount of energy, 3250 calories, is required to break it down in an endothermic manner.
Key points about endothermic processes are:

• The energy of the products is higher than that of the reactants.
• These processes often result in a decrease in temperature of the surroundings.
• Energy input is necessary for the reaction to occur.

By understanding these characteristics, we can better grasp why the decomposition reaction needs energy input. It reverses the exothermic reaction by utilizing the absorbed energy.

Chemical Decomposition

Chemical decomposition is a fascinating process where a compound or molecule is broken down into simpler substances. Think of it like taking apart a building made of blocks, piece by piece, until you're left with individual blocks.
In our exercise, ammonia is the compound being decomposed. This process involves separating ammonia back into its original components: hydrogen and nitrogen gases.
Decomposition requires energy because it is breaking down bonds. This is an endothermic process where the same amount of energy that was released when forming ammonia is needed to decompose it.
Important to keep in mind about chemical decomposition:

• It often involves breaking chemical bonds, which requires energy input.
• Decomposition might produce multiple simpler substances from one compound.
• It can occur naturally or can be induced with external factors such as heat.

Recognizing how chemical decomposition works gives insight into reaction mechanics and the energy considerations needed for practical applications.