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Chapter 3: Problem 9

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

Expert verified
The presence of water dripping from the exhaust of a car does not necessarily indicate that there was water in the original gasoline. Instead, it shows that water is a natural byproduct of the combustion process. The combustion of hydrocarbons in gasoline, such as octane, produces water vapor as shown in the chemical equation: \[2 \text{ C}_{8}\text{H}_{18} (l) + 25 \text{ O}_{2} (g) \rightarrow 16 \text{ CO}_{2} (g) + 18 \text{ H}_{2}\text{O} (g)\] This water vapor condenses into liquid water in the exhaust system and eventually drips out from the exhaust pipe.

Step by step solution

01

Understand the car's engine chemical reactions

In a car engine, gasoline (primarily composed of hydrocarbons like octane) reacts with oxygen in the air in a process called combustion. This combustion process releases energy in the form of heat and work, which powers the car. The balanced chemical reaction for the combustion of octane is given by: \[2 \text{ C}_{8}\text{H}_{18} (l) + 25 \text{ O}_{2} (g) \rightarrow 16 \text{ CO}_{2} (g) + 18 \text{ H}_{2}\text{O} (g)\] As seen in the above reaction, the products of octane combustion are carbon dioxide (CO鈧�) and water (H鈧侽).
02

Examine the water formation in the reaction

From the balanced chemical equation, 18 moles of water are produced for every 2 moles of octane molecules combusted. In reality, complete combustion may not occur in a car's engine due to various factors. However, even in incomplete combustion, a certain amount of water will still form as a byproduct. The water formed during the combustion process is initially in a gaseous state due to the high temperatures within the engine. As the exhaust gases move through the exhaust system and cool down, the gaseous water condenses into liquid form and accumulates in the exhaust. When enough liquid water has gathered, it drips out from the exhaust pipe.
03

Conclude if water was present in gasoline

Given the explanation above, the presence of water dripping from the exhaust of a car does not necessarily indicate that there was water in the original gasoline. Instead, it shows that water is a natural byproduct of the combustion process. Since the combustion of hydrocarbons in gasoline produces water vapor, which then condenses into liquid water, it is normal to observe water dripping from a car's exhaust.

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Most popular questions from this chapter

Ammonia reacts with \(\mathrm{O}_{2}\) to form either \(\mathrm{NO}(\mathrm{g})\) or \(\mathrm{NO}_{2}(\mathrm{~g})\) according to these unbalanced equations: $$ \begin{array}{l} \mathrm{NH}_{3}(\mathrm{~g})+\mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}(g)+\mathrm{H}_{2} \mathrm{O}(g) \\ \mathrm{NH}_{3}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g) \end{array} $$ In a certain experiment \(2.00 \mathrm{~mol} \mathrm{NH}_{3}(g)\) and \(10.00 \mathrm{~mol}\) \(\mathrm{O}_{2}(g)\) are contained in a closed flask. After the reaction is complete, \(6.75 \mathrm{~mol} \mathrm{O}_{2}(g)\) remains. Calculate the number of moles of \(\mathrm{NO}(g)\) in the product mixture: (Hint: You cannot do this problem by adding the balanced equations, because you cannot assume that the two reactions will occur with equal probability.)

Several important compounds contain only nitrogen and oxygen. Place the following compounds in order of increasing mass percent of nitrogen. a. NO, a gas formed by the reaction of \(\mathrm{N}_{2}\) with \(\mathrm{O}_{2}\) in internal combustion engines b. \(\mathrm{NO}_{2}\), a brown gas mainly responsible for the brownish color of photochemical smog c. \(\mathrm{N}_{2} \mathrm{O}_{4}\), a colorless liquid used as fuel in space shuttles d. \(\mathrm{N}_{2} \mathrm{O}\), a colorless gas sometimes used as an anesthetic by dentists (known as laughing gas)

Tetrodotoxin is a toxic chemical found in fugu pufferfish, a popular but rare delicacy in Japan. This compound has a \(\mathrm{LD}_{50}\) (the amount of substance that is lethal to \(50 . \%\) of a population sample) of \(10 . \mu \mathrm{g}\) per \(\mathrm{kg}\) of body mass. Tetrodotoxin is \(41.38 \%\) carbon by mass, \(13.16 \%\) nitrogen by mass, and \(5.37 \%\) hydrogen by mass, with the remaining amount consisting of oxygen. What is the empirical formula of tetrodotoxin? If three molecules of tetrodotoxin have a mass of \(1.59 \times 10^{-21} \mathrm{~g}\), what is the molecular formula of tetrodotoxin? What number of molecules of tetrodotoxin would be the LD \(_{50}\) dosage for a person weighing \(165 \mathrm{lb}\) ?

Methane \(\left(\mathrm{CH}_{4}\right)\) is the main component of marsh gas. Heating methane in the presence of sulfur produces carbon disulfide and hydrogen sulfide as the only products. a. Write the balanced chemical equation for the reaction of methane and sulfur. b. Calculate the theoretical yield of carbon disulfide when \(120 . \mathrm{g}\) of methane is reacted with an equal mass of sulfur.

Bauxite, the principal ore used in the production of aluminum, has a molecular formula of \(\mathrm{Al}_{2} \mathrm{O}_{3}=2 \mathrm{H}_{2} \mathrm{O}\). a. What is the molar mass of bauxite? b. What is the mass of aluminum in \(0.58\) mol bauxite? c. How many atoms of aluminum are in \(0.58 \mathrm{~mol}\) bauxite? d. What is the mass of \(2.1 \times 10^{24}\) formula units of bauxite?
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