
Concept explainers
In a typical automobile engine, a gasoline vapor-air mixture is compressed and ignited in the cylinders of the engine. This results in a combustion reaction that produces mainly carbon dioxide and water vapor. For simplicity, assume that the fuel is C8H18 and has a density of 0.760 g/mL.
- (a) Calculate the partial pressures of N2 and 02 in the air before it goes into the cylinder; assume the atmospheric pressure is 734 mmHg.
- (b) Consider the case where the air, without any fuel added, is compressed in the cylinder to seven times atmospheric pressure, the compression ratio of many modem automobile engines. Calculate the partial pressures of N2 and O2 at this pressure.
- (c) Now consider the case where 0.050 mL gasoline is added to the air in the cylinder just before compression and completely vaporized. Assume that the volume of the cylinder is 485 mL and the temperature is 150°C. Calculate the partial pressure of the gasoline vapor.
- (d) Calculate the amount (mol) of oxygen required to bum the gasoline in part (c) completely to CO2 and H2O.
- (e) The combustion reaction in the cylinder creates temperatures in excess of 1200K. Due to the high temperature, some of the nitrogen and oxygen in the air reacts to form nitrogen monoxide. If 10% of the nitrogen is converted to NO, calculate the mass (g) of NO produced by this combustion.
- (f) Hot-rod cars use another oxide of nitrogen, dinitrogen monoxide, to create an extra burst in power. When such a power boost is needed, dinitrogen monoxide gas is injected into the cylinders where it reacts with oxygen to form NO. Calculate the mass of dinitrogen monoxide that would have to be injected to form the same quantity of NO as produced in part (e). Assume that sufficient oxygen is present to do so.
(a)

Interpretation:
Partial pressure of
Concept Introduction:
Mole fraction: Quantity which defines the number of moles of a substance in a mixture divided by the total number of moles of all substances present.
Partial pressure of a gas in the mixture of gases is the product of mole fraction of the gas and the total pressure.
Answer to Problem ISP
Partial pressure of
Partial pressure of
Explanation of Solution
Percentage by volume of
Percentage by volume of
Mole fraction of
Partial pressure of
Partial pressure of
(b)

Interpretation:
Partial pressure of
Answer to Problem ISP
Partial pressure of
Partial pressure of
Explanation of Solution
At
According to Boyle’s law, pressure and volume is inversely proportional to each other at constant temperature and number of molecules.
Hence, when the volume of gas is compressed by seven times, then pressure of the sample is increased by seven times.
Therefore,
Partial pressure of
(c)

Interpretation:
Partial pressure of the gasoline vapor has to be calculated.
Concept Introduction:
Ideal gas Equation:
Any gas is described by using four terms namely pressure, volume, temperature and the amount of gas. Thus combining three laws namely Boyle’s, Charles’s Law and Avogadro’s Hypothesis the following equation could be obtained. It is referred as ideal gas equation.
Here,
n is the moles of gas
P is the Pressure
V is the Volume
T is the Temperature
R is the gas constant
Answer to Problem ISP
Partial pressure of the gasoline vapor is
Explanation of Solution
Given information is shown below,
Number of moles of gasoline
Partial pressure of the gasoline vapor can be calculated using Ideal Gas equation as follows,
(d)

Interpretation:
Number of moles of
Answer to Problem ISP
Number of moles of
Explanation of Solution
Balanced equation for the combustion of gasoline is given below,
Number of moles of gasoline
From the balanced equation, it is clear that
(e)

Interpretation:
Mass of
Concept Introduction:
Refer to (c)
Answer to Problem ISP
Mass of
Explanation of Solution
Given information is shown below,
Number of moles of
The reaction that shows the formation of
From the balanced equation, it is clear that
Mass of
(f)

Interpretation:
Mass of
Answer to Problem ISP
Mass of
Explanation of Solution
The reaction that shows the formation of
Number of moles of
From the balanced equation, it is clear that
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Chapter 8 Solutions
Chemistry: The Molecular Science
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