THE
GAS LAWS
BOYLE’S
LAW
States that the pressure of a fixed amount of gas at a
constant temperature is inversely proportional to the volume of the gas
Example
Problem:
The volume of the large, irregularly shaped, closed tank
is determined as follows. The tank is first evacuated, and then it is connected
to a 50.0L cylinder of compressed nitrogen gas. The gas pressure in the
cylinder, originally at 21.5 atm falls to 1.55 atm after it is connected to the
evacuated tank. What is the volume of the tank?
Practice
Exercises:
A cylinder contains a gas at 5.25 atm pressure. When the
gas is allowed to expand to a fix volume of 12.5L, the pressure drops to 1.85
atm. What was the original volume of the gas?
CHARLE’S
LAW
States that the volume of a fixed amount of gas at
constant pressure is directly proportional to the Kelvin (absolute) temperature
Another form of
Charles’s Law shows that at constant amount of gas and volume, the pressure of
a gas is proportional to temperature.
Example
Problem:
A balloon is inflated to a volume of 2.50 L in a warm
living room (24 C). Then it is taken outside on a very cold winter day (-25 C).
Assume that the quantity of air in the balloon and its pressure both remain
constant. What will be the volume of the balloon when it is outdoor?
Practice
Exercise:
A gas at 25 C and 0.987
atm pressure is confined in a cylinder by a piston. When the cylinder is heated
the gas volume expands from 0.250L to 1.65 L. What is the new temperature of
the gas, assuming the pressure remain constant.
AVOGADRO’S
LAW
Avogadro’s
Law can be stated in either of two ways:
1. Equal
volumes of different gases compared at the same temperature and pressure
contain equal number of molecules.
2. Equal
number of molecules of different gases compared at the same temperature and
pressure occupy equal volumes.
V
∞ n
V
= kn
Example
Problem
What is the mass of 1.00 L of
cyclopropane gas, C3H6 (used as an anesthetic), when measured STP?
Practice
Exercise:
THE
IDEAL GAS EQUATION
From the simple gas laws:
Ideal
Gas
– a hypothetical gas whose pressure-volume-temperature behavior can be completely accounted for by the
ideal gas equation.
Example
Problem:
What is the pressure exerted by 1.00 x 1020
molecules of N2 in a 305-mL flask at 170 ºC?
Practice Exercise:
How many moles of He
(g) are in a 5.00 L storage tank filled with He at 10.5 atm pressure at 30.0 ºC?
THE
GENERAL GAS EQUATION
The ideal gas equation
is useful for problems that do not involve changes in V, T and n for a gas
sample. Sometimes a gas is described under two different sets of condition. Here
we have to apply the ideal gas equation twice, to an initial condition and a
final condition. That is,
The
above expression are equal to each other because each is equal to R
Example Problem:
A small bubble rises from bottom of
a lake, where the temperature and pressure are 8°C and 6.4 atm, to the water’s
surface, where the temperature is 25°C and the pressure is 1.0 atm. Calculate
the final volume (in mL) of the bubble if its initial volume was 2.1 mL.
Practice Exercise:
1.
A
gas initially at 4.0 L, 12 atm and 66°C undergoes a change so that its final
volume and temperature are 1.7 L and 42°C What is its final pressure? Assume
that the number of moles remain unchanged.
2.
A
sample of diborane gas (B2H6), a substance that bursts
into flame when exposed to air, has a pressure of 245 torr at a temperature of
-150 ºC and a volume of 3.48 L. If conditions
are changed so that the temperature is 36 ºC and the pressure is
468 torr, what will be the volume of the sample?
RECORDED LECTURES
Ideal Gas Law Practice Problems
https://www.youtube.com/watch?v=TqLlfHBFY08
The Gas Laws
Definition
of an ideal gas, ideal gas law
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