Question

Most of gasoline consists of liquid hydrocarbons. If you examine the exhaust pipe of a running automobile you will observe that liquid water continually comes out of it. In addition, a gas is emitted that is known to contribute to the warming of our planet. Explain where the water and the gas come from and what the gas is.

Short answer

The water and carbon dioxide observed in a car's exhaust pipe come from the combustion of gasoline, which consists of hydrocarbons. When gasoline undergoes combustion in the engine, it reacts with oxygen in the air, producing carbon dioxide (CO2) and water (H2O). The water is produced due to the combination of hydrogen and oxygen atoms, while CO2 is a greenhouse gas that contributes to global warming. The balanced chemical equation for this combustion process is: \( C_xH_y + \frac{(x + \frac{y}{4})}{2} O_2 \rightarrow xCO_2 + \frac{y}{2}H_2O \)

Step-by-step solution

Understanding the combustion process in car engines

Gasoline is a mixture of hydrocarbons (consisting of carbon and hydrogen atoms). When gasoline burns in a car engine, it undergoes a combustion reaction with the oxygen in the air. The products of this reaction are primarily carbon dioxide (CO2), water (H2O), and various other gases.

Writing the general balanced chemical equation for gasoline combustion

The general chemical equation for the combustion of a hydrocarbon (CxHy) in the presence of oxygen (O2) is: \( C_xH_y + \frac{(x + \frac{y}{4})}{2} O_2 \rightarrow xCO_2 + \frac{y}{2}H_2O \) Here x and y represent the number of carbon and hydrogen atoms in the hydrocarbon, respectively.

Explaining the presence of water in car exhaust

The balanced chemical equation for the combustion of gasoline shows that water (H2O) is one of the products of the reaction. This is because the hydrogen atoms in the hydrocarbon combine with the oxygen atoms to form water molecules. Since engines produce heat, the water often comes out of the exhaust pipe in the form of steam, which cools and condenses back into liquid water.

Identifying the gas that contributes to global warming

Carbon dioxide (CO2) is the other main product of the combustion of gasoline, as shown in the balanced chemical equation above. CO2 is a greenhouse gas, meaning that it traps heat in the Earth's atmosphere and contributes to global warming.

Conclusion

The water and the gas (carbon dioxide) observed in the exhaust pipe of a running automobile come from the combustion of gasoline, a hydrocarbon fuel, in the car engine. The chemical reaction between the hydrocarbon and oxygen produces carbon dioxide, which contributes to global warming, and water as the primary products.

Key concepts

Chemical Reactions

A chemical reaction is a process that involves the transformation of one set of chemical substances to another through the breaking and formation of chemical bonds. It is fundamental to understanding the behavior of matter and explains numerous occurrences in our daily lives, from the rusting of metal to the baking of a cake. In the context of the hydrocarbons' combustion in car engines, these reactions involve hydrocarbons reacting with oxygen.

When you ignite the gasoline in a car engine, you are initiating a chemical reaction known as combustion. The hydrocarbons in gasoline, which are compounds made up of carbon (C) and hydrogen (H) atoms, react with oxygen (O) from the air. This reaction releases a significant amount of energy in the form of heat and light, propelling the vehicle forward. In addition to the energy released, this reaction also results in the creation of new substances: carbon dioxide (CO₂) and water vapor (H₂O). This process is essential for the functioning of automobiles but also has environmental implications that we must understand.

Balanced Chemical Equation

A balanced chemical equation is a representation of a chemical reaction that has equal numbers of atoms for each element involved in the reaction on both the reactant and product sides. It adheres to the law of conservation of mass, which states that matter cannot be created or destroyed in an isolated system.

The combustion of a hydrocarbon can be represented by a general balanced chemical equation. For instance, if the hydrocarbon formula is given as CₓHᵧ, then the balanced equation for its combustion is: \[ C_xH_y + \frac{(x + \frac{y}{4})}{2} O_2 \rightarrow xCO_2 + \frac{y}{2}H_2O \]This equation might look daunting at first, but let’s break it down. The term CₓHᵧ represents any hydrocarbon where 'x' is the number of carbon atoms, and 'y' is the number of hydrogen atoms. The reactant side also features oxygen (O₂), which is necessary for combustion. The products include carbon dioxide (CO₂) and water (H₂O). The coefficient before oxygen (O₂) is calculated to ensure the equation is balanced, providing equal numbers of atoms for each element on both sides.

Greenhouse Gases

Greenhouse gases are components of the Earth's atmosphere that can trap heat, effectively insulating the planet. This natural process is essential for maintaining the Earth's temperature and supporting life as we know it. However, an excess of these gases can lead to global warming, a central concern in climate change discussions.

Carbon dioxide (CO₂), the gas mentioned in the exercise as being emitted from a car's exhaust, is a significant greenhouse gas produced from burning fossil fuels like gasoline. When CO₂ is released into the atmosphere, it can absorb heat from the sun, preventing it from escaping back into space. While many gases share this property, CO₂ is of particular importance due to its long lifespan in the atmosphere and its close association with human activities, especially combustion of fossil fuels in vehicles and power plants.

It's crucial to understand that while combustion engines enable transportation and are central to the modern economy, they also contribute to the increased concentration of CO₂ in the atmosphere. This contribution underlines the need for cleaner energy resources and more efficient technologies to reduce emissions and mitigate the impact of greenhouse gases on climate change.