Problem 18 - Chemistry An Atoms First Approach

Question

Hydrogen reacts explosively with oxygen. However, a mixture of \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\) can exist indefinitely at room temperature. Explain why \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\) do not react under these conditions.

Step-by-Step Solution

Answer

Hydrogen and oxygen do not react explosively at room temperature because the average kinetic energy of the molecules is not sufficient to overcome the activation energy barrier required for the reaction to occur. In the absence of a catalyst or a higher temperature, hydrogen and oxygen can coexist indefinitely without undergoing an explosive reaction.

Step 1: Recall characteristics of chemical reactions

In a chemical reaction, reactants need to collide with each other at an appropriate orientation and sufficient energy for the reaction to take place. The minimum energy required for a successful collision is called the activation energy.

Step 2: Understand activation energy and reaction rates

Activation energy is the threshold energy that molecules need to attain in order for a chemical reaction to occur. If the molecules do not possess the required energy, they will not successfully react even if they collide with the proper orientation. The rate of a reaction depends on factors such as temperature, concentration, and presence of a catalyst.

Step 3: Consider room temperature conditions

At room temperature, the average kinetic energy of the hydrogen and oxygen molecules is relatively low. Consequently, most collisions between the molecules do not possess sufficient energy to overcome the activation energy barrier for the explosive reaction to occur.

Step 4: Role of a catalyst

A catalyst can lower the activation energy of a reaction, allowing it to occur more easily at lower temperatures. However, in this scenario, there is no catalyst present to initiate the explosive reaction between hydrogen and oxygen at room temperature.

Step 5: Conclusion

Hydrogen and oxygen do not react explosively at room temperature because the average kinetic energy of the molecules at this temperature is not high enough to overcome the activation energy barrier. In the absence of a catalyst or a higher temperature, these two gases can coexist indefinitely without undergoing a reaction.