Question

You may have noticed that water sometimes drips from the exhaust of a car as it is running. Is this evidence that there is at least a small amount of water originally present in the gasoline? Explain.

Short answer

The presence of water dripping from a car's exhaust does not necessarily indicate that there is a small amount of water originally present in the gasoline. This phenomenon occurs because water is a natural byproduct of the combustion process when hydrocarbons (gasoline) combine with oxygen to produce carbon dioxide (CO2) and water (H2O). As the water vapor travels through the cooling exhaust system, it can condense into liquid water and be expelled at the tailpipe in the form of drips.

Step-by-step solution

Understand the combustion process

In a car engine, gasoline (hydrocarbons) is burned in the presence of oxygen to release energy. This energy is then used to power the car. The combustion process can be represented by the following chemical equation: \[ C_xH_y + O_2 \rightarrow CO_2 + H_2O \] The hydrocarbon (gasoline) combines with oxygen to form carbon dioxide (CO2) and water (H2O).

Analyze the water formation during combustion

As seen in the combustion equation, water is a natural byproduct of the combustion process. When gasoline burns in the engine, it forms water vapor. The exhaust system then expels the leftover gases, including the water vapor.

Consider the role of temperature in water vapor condensation

As the water vapor travels through the exhaust system and the system cools down, it can condense into liquid water. This water is usually expelled at the tailpipe and may be observed as drips.

Conclusion

The presence of water dripping from a car's exhaust is not necessarily evidence that there is a small amount of water originally present in the gasoline. Instead, it can be explained by the combustion process and the formation of water vapor, which then condenses and exits the exhaust system as liquid water.