Gases - Saint Joseph High School
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Transcript Gases - Saint Joseph High School
Bell Work
Find the ΔH for the reaction below,
given the following reactions and
subsequent ΔH values:
2 SO2(g) + 2 P(s) + 5 Cl2(g) 2 SOCl2(l) + 2
POCl3(l)
SOCl2(l) + H2O(l) SO2(g) + 2 HCl(g)
ΔHo/kJ = +10.3
PCl3(l) + 1/2 O2(g) POCl3(l)
ΔHo/kJ = -325.7
P(s) + 3/2 Cl2(g) PCl3(l)
ΔHo/kJ = -306.7
4 HCl(g) + O2(g) 2 Cl2(g) + 2 H2O(l)
ΔHo/kJ = -202.6
What is the change in
temperature, if 3450J of heat
are added to a 23.4 gram
sample of Fe. (Specific heat of
iron is 0.444 J/g0C
Gases
Chapter 13
Properties
Uniformly fills a container
Easy to compress
Mixes completely with other gases
Exerts pressure on surroundings
Atmospheric pressure results from the mass of the
air being pulled toward the center of the earth by
gravity---weight of the air.
Units of pressure
mmHg (millimeters of mercury)
Torr
Torr and mmHg can be used interchangeably
Atm (standard atmosphere)
Pascal
Kinetic-Molecular theory
Gases can be compressed easily, but liquids and
solids cannot be compressed because particles are
already close together
The intermolecular forces between gases are weak.
Gas particles move until a collision alters their
course
Energy added into the system increases the kinetic
energy of the particles, which translates to an
increase in temperature of the gas.
Relationship between
pressure and volume
Boyle’s law- pressure times volume equals a
constant
P1V1=P2V2
Example of Boyle’s Law
A container holds 500. mL of CO2 at 20.° C and 742
torr. What will be the volume of the CO2 if the
pressure is increased to 795 torr?
V1=500mL
P1=742 torr
V2= x
P2=795 torr
(500mL)(742Torr)=(x)(795Torr)
X=470mL
Practice Problem
A gas tank holds 2785 L of propane, C3H8, at 830.
mm Hg. What is the volume of the propane at
standard pressure, 760mmHg?
V1P1 = V2P2
(2785L)(830mmHg)=(x)(760mmHg)
3042L
Relationship between
volume and temperature
Charles’s Law-gas volume is directly proportional
to the temperature
V1 = V2
T1 T 2
Temperature is in Kelvin (+273)
Example of Charles’s Law
A container holds 50.0 mL of nitrogen at 25° C and
a pressure of 736 mm Hg. What will its volume be,
if the temperature increases by 35° C?
V1 = V2
T1 T2
50mL = x
298K
333K
x= 56mL
Practice problem
A sample of helium has a volume of 521 dm3 at a
pressure of 75 cm Hg and a temperature of 18° C.
When the temperature is increased to 23° C, what
is the volume of the helium?
V1 = V2
T1 T2
521dm3 = x
291K
296K
=530dm3
Combined gas Law
P1V1 = P2V2
T1
T2
The combined gas law is a mix between Charles’s,
Boyle’s, and Gay-Lussac’s Laws
Example
A sample of argon has a volume of 5.0 dm3 and the
pressure is 0.92 atm. If the final temperature is 30.°
C, the final volume is 5.7 L, and the final pressure
is 800. mm Hg, what was the initial temperature of
the argon?
P1V1 = P2V2
T1
T2
(5.0dm3)(0.92atm) = (5.7L)(1.05atm)
x
303K
=233K
Practice problem
A sample of sulfur dioxide occupies a volume of
652 mL at 40.° C and 720 mm Hg. What volume
will the sulfur dioxide occupy at STP?
P1V1 = P2V2
T1
T2
(652mL)(720mmHg) = (x)(760mmHg)
313K
273K
539mL
Avogadro’s Law
States that the volume of gas is proportional to the
number of gas particles at constant temperature and
pressure.
I.E. A volume occupied by one mole of gas is 22.4L
when the temperature of the gas is at 0oC and its
pressure is at 1atm.
These conditions are referred to as standard
temperature and pressure (STP)
STP conditions
standards listed below
22.4 Liters
1 atm=760mmHg or Torr
273 K
Example of STP
Calculate the number of moles of nitrogen gas
produced and grams of sodium azide consumed if
115L of N2 results from a sodium azide explosion.
115L x 1mol
22.4L
=5.13 moles
Ideal gas Law
PV=nRT
P-pressure(atm)
V-volume(L)
n-number of moles (mol)
R-constant (0.0821L*atm/mol *K)
T-temperature (Kelvin)
Example
A reaction yields 3.75 L of nitrogen monoxide. The
volume is measured at 19°C and at a pressure of 1.10
atm. What mass of NO was produced by the reaction?
PV=nRT
(1.10atm)(3.75L) =x(0.0821L*atm/mol*K)(292K)
0.17moles
0.17mol x 30g/mol
5.1 g
Practice problem
What is the pressure inside a tank that has a
volume of 1.20 x 103 L and contains 12.0 kg of HCl
gas at a temperature of 18°C?
PV=nRT
(x)(1.20x103L)=(329mol)(0.0821L*atm/mol*K)(291K)
6.6atm