Question

The burning of gasoline in automobile engines is a chemical reaction. In light of the law of conservation of mass, explain what happens to the gasoline in your car's tank as you drive.

Short answer

The gasoline in the tank decreases in mass as it is burned to form carbon dioxide and water vapor, which are expelled into the atmosphere, abiding by the law of conservation of mass.

Step-by-step solution

Understanding the Law of Conservation of Mass

According to the law of conservation of mass, matter is neither created nor destroyed within a chemical reaction. This implies that the total mass of reactants used in a chemical reaction is equal to the total mass of the products formed.

Recognizing the Chemical Reaction in Engines

Gasoline is primarily composed of hydrocarbons. When gasoline is burned in an automobile engine, it undergoes a chemical reaction with oxygen from the air to produce carbon dioxide, water, and energy in the form of heat and light.

Describing the Mass Transformation

As you drive and burn gasoline, the mass of the gasoline in the car's tank decreases. This mass is not lost but is transformed into other substances, mainly carbon dioxide and water vapor. These substances are expelled from the car's exhaust system into the atmosphere.

Key concepts

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into new substances called products. This transformation involves the breaking and forming of chemical bonds and often results in the release or absorption of energy. For example, when you strike a match, the chemicals on the match head react with oxygen in the air causing a combustion reaction that releases light and heat.

To understand the science behind anything burning, such as gasoline in an engine, it's crucial to grasp that during a chemical reaction, atoms are rearranged to form new molecules but are never destroyed or created from nothing. The way atoms are rearranged defines the kind of chemical reaction taking place and the substances produced as a result.

Combustion of Gasoline

The combustion of gasoline is a type of chemical reaction called an oxidation reaction, where the hydrocarbons in gasoline react with oxygen. When you start your car, the gasoline from the tank is drawn into the engine's combustion chamber, where it mixes with air. Upon ignition, the hydrocarbons in the gasoline undergo combustion, primarily forming carbon dioxide \( CO_2 \) and water \( H_2O \) as products, along with the release of significant energy in the form of heat and light - powering the vehicle.

It's fascinating to note that the gasoline itself is composed of a complex mixture of molecules, each consisting of hydrogen \( H \) and carbon \( C \) atoms, and sometimes including other elements as well. This complex mixture allows for the intense energy release that's harnessed to move your car.

Mass Transformation in Chemical Reactions

In the context of the combustion of gasoline, mass transformation occurs as the law of conservation of mass dictates. Essentially, the mass of the gasoline (hydrocarbons) and oxygen that react is exactly equal to the mass of the carbon dioxide, water, and any other byproducts produced, even though the substances themselves have changed form. The mass isn't lost; instead, it is transformed and conserved.

This principle also explains why your car's gas tank gets lighter as you drive. The hydrocarbon molecules from the gasoline are transformed into different molecules, mainly carbon dioxide and water vapor. These new compounds are then released into the atmosphere through your car's exhaust, illustrating the conservation of mass on a practical level.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships that govern a chemical reaction. It can be seen as the 'recipe' for a chemical reaction, allowing scientists and engineers to calculate precisely how much of each reactant is needed to produce the desired amount of product.

For instance, in the combustion of gasoline, stoichiometry helps in calculating the amount of oxygen required to burn a certain amount of gasoline completely. This also relates to the efficiency of the engine and the resulting emissions. By using the balanced chemical equation of the combustion reaction, one can ensure that the engine is supplied with the correct mixture of gasoline and air for optimal performance and minimal environmental impact.