Question

The decomposition of \(10.0 \mathrm{~g}\) of ammonia requires \(27,200 \mathrm{~J}\) of energy to give hydrogen and nitrogen gases. How much energy is released when hydrogen and nitrogen gases react to produce \(10.0 \mathrm{~g}\) of ammonia?

Short answer

27,200 J of energy is released when forming 10.0 g of ammonia from N₂ and H₂.

Step-by-step solution

Understanding the Reaction

The decomposition of ammonia (NH₃) into nitrogen (N₂) and hydrogen (H₂) is an endothermic process, meaning it requires energy to occur. The energy needed for this reaction is 27,200 J for 10.0 g of NH₃.

Reverse the Reaction

In the reverse reaction, where nitrogen and hydrogen gases combine to form ammonia, the process is exothermic. This means energy will be released.

Conservation of Energy

According to the conservation of energy, the energy required to decompose 10.0 g of ammonia is equal to the energy released when the same amount is formed from nitrogen and hydrogen. Therefore, if decomposing 10.0 g of ammonia requires 27,200 J, then forming 10.0 g from N₂ and H₂ will release the same amount: 27,200 J.

Key concepts

Endothermic Process

Endothermic processes are fascinating because they absorb energy from the surroundings. In this context, the decomposition of ammonia into nitrogen and hydrogen gases is a prime example. When a chemical reaction is endothermic, it requires an input of energy to proceed.

Here are key points about endothermic processes:

• They absorb heat from their environment, leading to a decrease in temperature.
• The energy absorbed is used to break chemical bonds in the reactants.
• After the process, the products have higher energy than the reactants.

In our example, decomposing 10 grams of ammonia requires 27,200 J of energy, emphasizing that energy input is crucial for the process to occur.

Exothermic Process

Conversely, an exothermic process releases energy to the surroundings. Such reactions are typically the reverse of endothermic ones. In our case, the formation of ammonia from nitrogen and hydrogen gases is exothermic.

Characteristics of exothermic processes include:

• Heat is released, often increasing the temperature of the environment.
• Energy is emitted when new chemical bonds form in the products.
• The products' energy state is lower than that of the reactants.

For the synthesis of ammonia, 27,200 J of energy is released when 10 grams of the compound are formed. The reversal of the endothermic decomposition process confirms the release of energy during product formation.

Conservation of Energy

The principle of conservation of energy is fundamental in chemistry. It states that energy cannot be created or destroyed, only transformed. This concept is vital in understanding chemical reactions.

In both endothermic and exothermic reactions:

• The total energy in a system remains constant.
• Energy absorbed during the endothermic decomposition is exactly equal to the energy released in an exothermic reaction.
• In our scenario, 27,200 J is both required and released when ammonia decomposes and then reforms, demonstrating energy conservation.

The idea that energy simply changes forms without loss reinforces the predictability of chemical reactions and the balance within closed systems.