Chemistry Unit 11 Guided Notes
Ch. 11.1 Pressure & its Units
Pressure
 Pressure (P) is defined as the ____________ ________
–
_________ __________ on a surface.
P = ____________ / _______________
 In SI, pressure is expressed in pascals (Pa).
 One pascal is a very small unit of pressure, so in many cases, it is more convenient to express
pressure in _______________________ (kPa).
Measuring Pressure
• A __________________ is a device used to measure atmospheric pressure. –
Invented by Torricelli in 1643
• Tube containing column of mercury supported by pressure of air.
• Pressure is directly related to the _______________of the mercury.
• Commonly measured as millimeters of mercury (mm Hg).
Other Units of Pressure
• Atmosphere (atm)
– 1 atm defined to be the pressure at sea level when temperature is 0°C.
– 1 atm = 760 mm Hg = 760 Torr (torr)
What Do You Think?
The average atmospheric pressure in Denver, Colorado is 0.830 atm. Express this pressure in
a. millimeters of mercury (mm Hg)
b. kilopascals (kPa)
Ch. 11.2 Gas Laws
Boyle’s Law: Pressure-Volume Relationship
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Boyle’s Law states that the volume of a gas varies _____________ with the pressure at a
constant temperature.
Boyle’s law can also be expressed mathematically as:
o P1 V1 =
P1 and V1 represent original conditions, and P2 and V2 represent new set of conditions.
Sample Problem 1
A sample of helium gas collected at 750 mm Hg occupies a volume of 250 mL. What pressure does
the gas exert if the volume increases to 300 mL?
Charles’s Law: Volume-Temperature Relationship
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Charles’s law states that the volume of a gas varies directly with the Kelvin temperature at a
______________ pressure.
(K = °C + 273)
Gas volume and Kelvin temperature are _____________ proportional to each other as shown
at right.
Charles’s law can be expressed mathematically as:

V1 and T1 represent original conditions, and V2 and T2 represent new set of conditions.
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In order to use this equation the temperature must be in Kelvin.
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Sample Problem 2
A sample of neon gas occupies a volume of 752 mL at 25°C. What volume will the gas occupy at
50°C if the pressure remains constant?
Gay-Lussac’s Law: Pressure-Temperature Relationship
• Gay-Lussac’s law states that the pressure of a gas varies __________ with the Kelvin temperature
at a constant volume.
• Gay-Lussac’s law can be mathematically expressed as:
• P1 and T1 represent original conditions, and P2 and T2 represent new set of conditions.
• Temperatures must be in ___________ to use this equation.
Sample Problem 3
The gas in a container is at a pressure of 3.00 atm at 25°C. Directions on the container warn the user
not to keep it in a place where the temperature exceeds 52°C. What would the gas pressure in the
container be at 52°C?
Ch. 11.3 The Combined Gas Law
• Boyle’s law, Charles’s law, and Gay-Lussac’s law can be combined into a single equation
that can be used for situations in which temperature, pressure, and volume, all vary at the same time.
• The combined gas law can be written as:
Standard Temperature and Pressure
• As a reference point used for comparing gases, scientists have agreed on standard
conditions.
• Standard Temperature – 0°C or _____ K
• Standard Pressure – 1 atm
• These conditions are commonly abbreviated as _______.
Sample Problem 4
A helium-filled balloon has a volume of 50.0 L at 25°C and 162 kPa. What volume will it have at
STP?
Relationship Between Volume and Particles
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Studied by Italian scientist named Amadeo Avogadro.
He noted that under constant temperature and pressure, the _____________ of a gas is
directly related to the number of particles (____________) of gas.
This is known as Avogadro’s law.
From his observations, he noticed that equal volumes of gases at the same temperature and
pressure contain the same number of particles.
The volume occupied by one mole of gas at STP is known as the standard ____________
____________ of a gas, which is 22.4 L.
Problems Involving Standard Molar Volume
a) What volume does 0.0685 mol of He gas occupy at STP?
b) What quantity of gas, in moles, is contained in 6.41 L of CO2 at STP?
Ch. 11.4 Ideal Gas Law
Warm Up:
The reaction shown represents the oxidation of ammonia (NH3).
4NH3 + 5 O24NO+ 6H2O
1. How many moles of water will be formed from 34 grams of ammonia?
2. What volume, in liters, will 75.4 grams of O2 occupy at STP?
Ideal Gas Law
•
Ideal gas law: mathematical relationship among pressure, volume, temperature, and number of
moles of a gas.
PV = nRT
•
R is known as the ideal gas constant.
R = 0.0821 L atm/mol K
*Be sure to match the units of the known quantities and the units of R*
Sample Problems
1.
25°?
What is the pressure exerted by a 0.475 mol sample of nitrogen gas in a 10.0 L container at
2.
Calculate the mass of 675 mL of NH3 at 725 mm Hg at 27°C.
Comparing the Volumes of Reacting Gases
• In the early 1800s, Gay-Lussac observed that when gases reacted, they did so in _____________
and ________________ volume proportions.
• Example: hydrogen gas + oxygen gas → water vapor
2 L (2 volumes) +1 L (1 volume) 2 L (2 volumes)
• Gay-Lussac’s law of combining volumes of gases states that at constant temperature and pressure,
the volumes of gaseous reactants and products can be expressed as ratios of small whole numbers.
• The coefficients in chemical equations of gas reactions reflect not only molar ratios, but also
________________ ________________.
– Example:
2CO(g) + O2(g) → 2CO2(g)
2 mole + 1 mole  2 mole or 2 volumes + 1 volume  2 volumes
Sample Problem
The complete combustion of propane, C3H8, occurs according to the following balanced equation.
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
How many liters of oxygen (O2) will be required for the complete combustion of 0.350 L of propane?
Ch. 11.5 Gas Stoichiometry
The industrial production of ammonia (NH3) proceeds according to the following equation:
N2(g) + 3H2(g) → 2 NH3(g)
If 20.0 mol of nitrogen (N2) is available, how many liters of NH3 can be produced at STP?
EOC Sample Question
The equation represents the breakdown of potassium chlorate (KClO3)
2KClO3 2KCl + 3O2
What volume of oxygen gas (O2) does 20.0 grams of potassium chlorate (KClO3) produce at STP
based on the equation shown?
A. 5.48 L
B. 7.80 L
C. 67.3 L
D. 72.9 L