Gases Chemistry Worksheet - Chapter 13, An Introduction To Chemistry Page 10
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Chapter 13
Gases
Gases and the Internal Combustion Engine
Now, let’s apply our model for gases to a real situation. Because the changes that take
place in a typical car engine illustrate many of the characteristics of gases, let’s take a
look at how the internal combustion engine works (Figure 13.8).
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Liquid gasoline is a mixture of hydrocarbons, with from five to twelve carbon atoms
bjeCtive
in each molecule. It evaporates to form a gas, which is mixed with air and injected into
the engine’s cylinders. (See cylinder 1 in Figure 13.8.) The movement of the engine’s
pistons turns a crankshaft that causes the piston in one of the cylinders containing the
gasoline-air mixture to move up, compressing the gases and increasing the pressure of
the gas mixture in the cylinder. (See cylinder 2 in Figure 13.8.)
A spark ignites the mixture of compressed gases in a cylinder, and the hydrocarbon
compounds in the gasoline react with the oxygen in the air to form carbon dioxide gas
and water vapor. (See cylinder 3 in Figure 13.8.) A typical reaction is
( g ) + 25O
→ 16CO
( g ) + 18H
2C
H
( g)
O(g ) +
Energy
8
18
2
2
2
2 mol + 25 mol = 27 mol
16 mol + 18 mol = 34 mol
In this representative reaction, a total of 27 moles of gas are converted into 34 moles of
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gas. The increase in moles of gas leads to an increase in number of collisions per second
with the walls of the cylinder, which creates greater force acting against the walls and a
greater gas pressure in the cylinder. The pressure is increased even more by the increase
in the temperature of the gas due to the energy released in the reaction. The increased
temperature increases the average velocity of the gas particles, which leads to more
frequent collisions with the walls and a greater average force per collision.
The increased pressure of the gas pushes the piston down. (See cylinder 4 in Figure
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11
bjeCtive
13.8.) This movement of the pistons turns the crankshaft, which, through a series of
mechanical connections, turns the wheels of the car.
e combustion of the gasoline leads to an increase in
moles of gas, which also causes the gas pressure to increase.
Decreased volume leads to
e reaction is exothermic, so the temperature
increased gas pressure inside
of the product gases increases, contributing to
the cylinder.
the increased gas pressure.
1
3
Gaseous gasoline
2
4
e increased pressure pushes the piston
mixed with air
down, turning the crankshaft and
moves into the
ultimately the car's wheels.
cylinder.
Cylinder
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bjeCtive
Piston
Figure 13.8
Gases and the Internal
Crankshaft
Combustion Engine
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