### 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
 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
 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
```