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Chapter 5: GASES

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Chapter 5: GASES

In this chapter we will:

Define units of pressure and volume Explore the properties of gases Relate how the pressure, volume,

and temperature of gases are related

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Characteristics of Gases

Uniformly fills any container. Are highly compressible Mixes completely with any other

gas Exert pressure on its

surroundings.

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Pressure

Pressure is the force acting on an

object per unit area: P = F/A

Gravity exerts a pressure on the earth’s

atmosphere

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Pressure

The pressure of a 1 m2 column of air on earth exerts a pressure of about 100 kPa

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Units of Pressure

SI units = Newton/meter2 = 1 Pascal (Pa)

101,325 Pa = 101.325 kPa =

1 atmosphere = 1 atm

1 atm = 760 mm Hg = 760 torr

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PressureAtmospheric Pressure and the Barometer

Atmospheric pressure is measured with a barometer.

Standard atmospheric pressure is the pressure required to support 760 mm of Hg in a column

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Units of Pressure

The manometer above is another tool used to measure pressure. How would you measure how much pressure is being exerted on the column of mercury?

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Gas Laws: Boyle’s Law

The volume of a fixed quantity of gas is inversely proportionalto its pressure

Pressure Volume = Constant (T = constant)

P1V1 = P2V2 (T = constant)

V 1/P (T = constant)

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Gas Laws: Boyle’s Law

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Gas Laws: Charles’s Law

The volume of a gas is directly proportional to temperature

V = constant • T (P = constant)V/T = constant

VT

VT

P1

1

2

2 ( constant)

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Gas Laws: Charles’s Law

The plot of V vs. T is a straight line. What does that tell us about the relationship between V and T?

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Gas Laws: Gay-Lussac’s Law Gay-Lussac’s Law

Gay-Lussac’s Law of Combining Volumes:Gay-Lussac’s Law of Combining Volumes:

at a given T and P the volume of gases which react are small whole number ratios.

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Gas Laws: Avogadro’s Law

For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas

V = constant • n

n = number of moles of gas

22.4 L of any gas at 0° C contains 6.02x1023 gas molecules

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The Meaning of Temperature

Temperature measures the average kinetic energy of atoms (higher T means greater motion.)

We use the Kelvin temperature scale as an index of the random motions of gas particles.

(KE)32avg RT

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Standard Temperature and Pressure

“STP” P = 1 atm T = 0C = 273 K The molar volume of an ideal gas is

22.42 liters at STP

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The Ideal Gas Law

An equation of state for a gas. “state” is the condition of the gas at a

given time.PV = nRT

R = Ideal Gas constant = 0.08206 L atm mol

P = pressure in atm

V = volume in liters

n = moles

T = temperature in Kelvins

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The Ideal Gas Law

Sample Exercise: A sample of H2 has a volume of 8.56 L at a temperature of 0° C and a pressure of 1.5 atm. Calculate the moles of H2 molecules present in this gas sample.

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The Ideal Gas Law

Sample Exercise 2: A sample of gas contains 0.35 mol of argon gas at a temperature of 13°C and a pressure of 568 torr is heated to 56°C and a pressure of 897 torr. Calculate the change in volume that occurs.