Monday, October 29th
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Gas Laws.. So Far
Pressure Units
1 atm= 760 torr,
1 atm= 760 mmHg
Relationships P, V, T
P and V- Increase Pressure, Decrease Volume
V and T- Increase Temp., Increase Volume
P and T- Increase Temp., Increase Pressure
Clicker Review #1
If the temperature of a gas in a closed container doubles, what is
the final pressure if it was initially 1atm?
a) 0.5 atm
c) 2 atm
b) 1 atm
d) 4 atm
Clicker Review #2
How many mmHg are in 1.0 atm?
a) 670
c) 1000
b) 760
d) 273
Clicker Review #3
If the temperature in a system stays constant and the volume gets
cut in half, what happens to the pressure if it was initially 3 atm?
a) 6 atm
c) 3 atm
b) 1.5 atm
d) 9 atm
Combined Gas Law
The combined gas law uses Boyle’s Law, Charles’s
Law, and Gay-Lussac’s Law (n is constant).
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Learning Check
A gas has a volume of 675 mL at 35.0 °C and 0.850 atm
pressure. What is the volume (mL) of the gas at −95.0 °C and
a pressure of 802 mmHg (n constant)?
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Solution
A gas has a volume of 675 mL at 35.0 °C and 0.850 atm
pressure. What is the volume (mL) of the gas at −95.0 °C and a
pressure of 802 mmHg (n constant)?
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Avogadro’s Law: Volume
and Moles
Avogadro’s law states that:
• the volume of a gas is
directly related to the
number of moles (n) of gas.
• T and P are constant.
© 2013 Pearson Education, Inc.
Chapter 7, Section 7
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Learning Check
If 0.75 mole of helium gas occupies a volume of 1.5 L, what
volume will 1.2 moles of helium occupy at the same
temperature and pressure?
© 2013 Pearson Education, Inc.
Chapter 7, Section 7
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Solution
If 0.75 mole of helium gas occupies a volume of 1.5 L, what
volume will 1.2 moles of helium occupy at the same
temperature and pressure?
Rearrange the gas law equation to solve for
the unknown quantity.
Substitute values into the gas law equation
and calculate.
STP
To make comparisons between different gases, we use
arbitrary conditions called standard temperature (273 K)
and standard pressure (1 atm). Standard temperature and
pressure is abbreviated as STP.
Standard temperature (T) = 0 C or 273 K
Standard pressure (P) = 1 atm (760 mmHg)
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Molar Volume
The molar volume of a gas measured at STP (standard
temperature and pressure) is 22.4 L for 1 mole of any gas.
Avogadro’s law indicates that 1 mole of any gas at STP has a
volume of 22.4 L.
© 2013 Pearson Education, Inc.
Chapter 7, Section 7
13
Molar Volume as a
Conversion Factor
The molar volume at STP
• has about the same volume as 3
basketballs.
• can be used to form 2 conversion factors.
and
© 2013 Pearson Education, Inc.
Chapter 7, Section 7
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Using Molar Volume
What is the volume occupied by 2.75 moles of N2 gas at
STP?
© 2013 Pearson Education, Inc.
Chapter 7, Section 7
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Using Molar Volume
What is the volume occupied by 2.75 moles of N2 gas at STP?
Write the equalities and conversion factors
including 22.4 L/mole at STP.
Set up the problem with factors to cancel units.
© 2013 Pearson Education, Inc.
Chapter 7, Section 7
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Ideal Gas Law
The four properties used in the measurement of a gas,
• pressure (P),
• volume (V),
• temperature (T), and
• amount (n),
can be combined to give a single expression called the
ideal gas law. PV = nRT
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R, Ideal Gas Constant
Rearranging the ideal gas law equation shows that the four gas
properties equal a constant, R.
To calculate the value of R, we substitute the STP
conditions for molar volume into the expression:
Learning Check
Another value for the universal gas constant, R, is obtained
using mmHg for the STP pressure. What is the value of R
when a pressure of 760 mmHg rather than 1.00 atm is used?
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Solution
Another value for the universal gas constant, R, is
obtained using mmHg for the STP pressure. What
is the value of R when a pressure of 760 mmHg
rather than 1.00 atm is used?
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Unit Summary for R, the Ideal
Gas Constant
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Learning Check
Dinitrogen oxide (N2O), laughing gas, is used by dentists as
an anesthetic. If a 20.0 L tank of laughing gas contains 2.86
moles of N2O at 23 C, what is the pressure (mmHg) in the
tank?
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Solution
If a 20.0 L tank of laughing gas contains 2.86 moles of N2O at 23
˚C, what is the pressure (mmHg) in the tank?
Rearrange the ideal gas law equation to solve
for the needed quantity.
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Review
Quiz Review #1
The volume of 1 mole of a gas is 22.4L, how many moles does
11.2L have?
a) 2
c) 0.5
b) 4
d) 0.25
Quiz Review #2
The n in the ideal gas law stands for?
a) moles
c) pressure
b) gas constant
d) nano
Quiz review #3
If the volume of gas in a closed system doubles and the
temperature stays constant, what happens to the pressure?
a) doubles
c) halves
b) same
d) triples
Quiz Practice #4
A gas is initially 134.6mL at 1.254 atm and 87.3◦C. If the
pressure shifted to 0.3451 atm and the volume increased to
232.1mL, what is the final temp in celsius?
Quiz Practice #5
How many moles of N2 occupy a volume of 34.5L at 1.256 atm
and 267K?
Wednesday
Quiz - Written, Chapter 7
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