What is the primary cause of chemical explosions?

The primary cause of chemical explosions is the rapid combination of fuel and oxygen that supports combustion. When fuel ignites, it reacts with oxygen in the air, creating heat and releasing gas. This gas expands quickly, causing a sudden increase in pressure, which can lead to an explosion if it occurs in a confined space. The efficiency of this process relies on the presence of both a combustible material (fuel) and an oxidizer (usually oxygen from the air).

In contrast, the other options present scenarios that may contribute to explosions but do not primarily account for chemical reactions leading to explosive results. For instance, while the reaction of water and acid can generate heat and gas, it does not typically lead to an explosion unless other conditions are present. Temperature changes can result in pressure changes but are not the main driving force behind chemical explosions. Similarly, mechanical failure in storage containers may lead to an explosion in certain circumstances but is not a fundamental chemical reaction like the combustion process.