# gases and their behavior

```GASES AND THEIR
BEHAVIOR
Chapter 5
Properties of Gases
• Only 4 quantities are needed to define the
state of a gas:
• 1). The quantity of the gas, n (in moles)
• 2). The temperature of the gas, T (Kelvin)
• 3). The volume of a gas , V (Liters)
1000mL=1L
• 4). The pressure of the gas, P
(atmospheres)
Gas Pressure
• A measure of the force that it exerts on its
container. Force is the physical quantity
that interferes with inertia. Gravity is the
force responsible for weight.
• Force = Mass x acceleration, Newton’s 2nd
law.
• N = kg x m/s2
• Pressure – Force/unit area; N/m2
• Barometer – invented by Evangelista
Torricelli in 1643. Uses the height of a
column of mercury to measure gas
pressure (especially atmospheric)
• 1mmHg = 1torr
• 760mmHg = 760torr = 1atm = 101.325kPa
• 101.325kPa = 14.7psi (pounds per square
inch)
Practice problems
• 515mmHg in kPa
727mmHg into kPa
52.5kPa into atm
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1. 52.5kPa into atm
2. 0.729atm into mmHg
3. 522torr into kPa
4. 1.10atm into psi
5. 800mmHg into atm
6. 125kPa into torr
7. Rank the following pressures in decreasing
order of magnitude (largest first, smallest last):
75kPa, 300torr, 0.60atm and 350mmHg
Gas Laws: The experimental basis
• Boyle’s law: The father of chemistry.
• His law states the volume of a confined gas is
inversely proportional to the pressure exerted
on the gas.
• Pressure and volume are inversely proportional
• Temperature is constant
• For a given quantity of a gas at constant
temperature, the product of pressure and
volume is a constant.
• P1V1 = P2V2
Example
• A Sample of carbon dioxide with a
pressure of 55mmHg and a volume of
125mL is placed in a new flask. The
pressure of the gas in the new flask is
78mmHg. What is the volume of the new
Charles law
• If a given quantity of gas is held at a
constant pressure, then its volume is
directly proportional to the Absolute
temperature. Must use Kelvin
• V1T2=V2T1
• Avogadro’s law says that for a gas at constant
temperature and pressure , the volume is
directly proportional to the number of moles of
gas.
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V1n2=V2n1
V1= Initial volume
n1 = initial number of moles
V2= final volume
n2= final number of moles
• A 5.20L sample at 18C and 2.00 atm
pressure contains 0.436 moles of a gas. If
we add an additional 1.27moles of the gas
at the same temperature and pressure,
what will the total volume occupied by the
gas be.
• Suppose we have a 12.2L sample
containing 0.50mol oxygen gas(O2) at a
pressure of 1atm and a temperature of
25C. If all this 02 were converted to ozone
at the same temperature and pressure,
what would be the volume of the ozone?
• Charles’s Law
• 1) If I have 45 liters of helium in a balloon
at 250 C and increase the temperature of
the balloon to 550 C, what will the new
volume of the balloon be?
•
• 3) I have 130 liters of gas in a piston at a
temperature of 2500 C. If I cool the gas
until the volume decreases to 85 liters,
what will temperature of the gas be?
• 2) Calcium carbonate decomposes at
12000 C to form carbon dioxide and
calcium oxide. If 25 liters of carbon
dioxide are collected at 12000 C, what will
the volume of this gas be after it cools to
250 C?
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