Question

In a classroom demonstration, hydrogen gas and oxygen gas are mixed in a balloon. The mixture is stable under normal conditions, but, if a spark is applied to it or some powdered metal is added, the mixture explodes. (a) Is the spark acting as a catalyst? Explain. (b) Is the metal acting as a catalyst? Explain.

Short answer

No, the spark is not a catalyst. Yes, the powdered metal can be a catalyst.

Step-by-step solution

- Understand what a catalyst is

A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It lowers the activation energy needed for the reaction to proceed.

- Determine if the spark acts as a catalyst

Examine whether the spark is consumed in the reaction or simply initiates it. A spark provides the activation energy required for the hydrogen and oxygen reaction but is not a substance nor reusable in multiple reactions. It initiates but doesn't lower the activation energy itself.

- Conclusion on the spark

The spark is not a catalyst because it is not a substance that changes the reaction rate by lowering activation energy. It's simply an external energy source to start the reaction.

- Determine if the metal acts as a catalyst

Check if the powdered metal is consumed in the reaction or remains unchanged. A catalyst should be reusable and lower the activation energy. The metal, if acting as a catalytic surface, can speed up the reaction without being used up in the process.

- Conclusion on the metal

If the powdered metal remains unchanged after initiating the explosion and can be reused, it acts as a catalyst. It lowers the activation energy required for the reaction between hydrogen and oxygen.

Key concepts

Activation Energy

To understand catalysts in chemical reactions, we first need to discuss the concept of activation energy. Activation energy is the minimum amount of energy required to initiate a chemical reaction. Think of it as the initial push needed to start a car's engine. Without this push, the reactants will not have enough energy to break their bonds and form new ones.
In the case of the hydrogen and oxygen reaction in the balloon, the activation energy is the energy needed to break the bonds in the hydrogen and oxygen molecules. Once the activation energy is provided, the reaction can proceed and produce water and energy in the form of an explosion.
For many reactions, activation energy is a crucial factor that determines the reaction rate. Higher activation energy means that fewer molecules will have enough energy to react at a given temperature. Catalysts play a crucial role here by lowering the activation energy, making it easier for the reaction to occur.

Hydrogen and Oxygen Reaction

The specific reaction we are looking at is the combination of hydrogen (H₂) and oxygen (O₂) gases, forming water (H₂O). The chemical equation for this reaction is:
2H₂(g) + O₂(g) → 2H₂O(l) + Energy
Under normal conditions, hydrogen and oxygen gases are quite stable. They do not react with each other quickly because the activation energy for this reaction is relatively high.
When a spark is introduced to the mixture, it provides the necessary activation energy. This energy excites the hydrogen and oxygen molecules, allowing them to overcome the activation energy barrier. Once the initial molecules react, they release a lot of energy, which triggers other hydrogen and oxygen molecules to react in a chain reaction, leading to an explosion. The spark serves to start this exothermic reaction but is not involved in lowering the activation energy.

Chemical Reaction Initiation

Chemical reactions often need an external force or agent to initiate, especially if the reactants are stable under normal conditions. In our exercise, both a spark and powdered metal were proposed as initiators.
A spark acts as an energy provider. It supplies the necessary activation energy to start the reaction. However, it is not a catalyst because it does not lower the activation energy nor is it reusable in multiple reactions.
On the other hand, if powdered metal is used, it can act differently. Metals like platinum or palladium can serve as catalysts in such reactions. Here’s how they work:

• The metal provides a surface for the hydrogen and oxygen molecules to come closer together.
• It weakens the bonds in the reactant molecules, effectively lowering the activation energy.
• The metal remains unchanged at the end of the reaction, meaning it can be reused.

Thus, metal can act as a true catalyst by lowering the activation energy needed for the hydrogen and oxygen reaction, unlike the spark, which merely ignites the reaction.