chapter 61 properties of gases expand to completely fill their container take the shape of their...
TRANSCRIPT
Chapter 6 1
Properties of Gases• Expand to completely fill their container• Take the shape of their container• Low density
– Much less than solid or liquid state
• Compressible• Mixtures of gases are always homogeneous• Fluid
Chapter 6 2
Gas Laws – Kinetic Molecular Theory
1. All matter is composed of tiny discrete particles called molecules
2. Molecules in a gas are in rapid constant motion and move in straight lines
3. Molecules of a gas are tiny compared with distances between gas molecules
4. There is little attraction between molecules of a gas
Chapter 6 3
5. Molecules collide with each other, with energy being conserved in the collision
6. Temperature (T) is a measure of the average kinetic energy of the gas molecules
Chapter 6 4
Pressure and Temperature (cont.)
Chapter 6 5
Volume Relationships• Law of combining volumes – when all
measurements are made at same temperature and pressure, volumes of gaseous reactants and products are in small whole-number ratio
Chapter 6 6
• Avogadro’s hypothesis – equal volumes of gases at constant pressure and temperature have the same number of molecules
Chapter 6 7
UNITS
• Pressure
• Temperature
Chapter 6 8
Molar Volume• Volume occupied by 1 mol of gas
• Standard temperature and pressure (STP)– 1 atm pressure and 0°C– 1 mole of gas has volume of 22.4 L
Chapter 6 9
Talk about Density
• This is at STP
Chapter 6 10
Boyle’s Law• PV=PV
Chapter 6 11
Talk about Lungs
A gas is enclosed in a cylinder fitted with a piston. The volume of the gas is 2.00 L at 0.524 atm. The piston is moved to increase the gas pressure to 5.15 atm. Which of the following is a reasonable value for the volume of the gas at the greater pressure?
0.20 L 0.40 L 1.00 L 16.0 L
A gas is enclosed in a 10.2-L tank at 1208 mmHg. (The mmHg is a pressure unit; 760 mmHg = 1 atm.) Which of the following is a reasonable value for the pressure when the gas is transferred to a 30.0-L tank?
300 mmHg 400 mmHg 3,600 mmHg12,000 mmHg
Exercise
EXAMPLE Boyle's Law: Pressure-Volume Relationships
A cylinder of oxygen has a volume of 2.25 L. The pressure of the gas is 1470 pounds per square inch (psi) at 20 °C. What volume will the oxygen occupy at standard atmospheric pressure (14.7 psi) assuming no temperature change?
EXAMPLE Boyle’s Law: Pressure-Volume Relationships
Chapter 6 14
EXAMPLE Boyle’s Law: Pressure-Volume Relationshipscontinued
A sample of air occupies 73.3 mL at 98.7 atm and 0 ºC. What volume will the air occupy at 4.02 atm and 0 ºC?
Exercise 2
A sample of helium occupies 535 mL at 988 mmHg and 25 °C. If the sample is transferred to a 1.05-L flask at 25 °C, what will be the gas pressure in the flask?
Exercise 3
Chapter 6 15
Charles’s Law
Chapter 6 16
Charles' Law• V/T = V/T
A balloon indoors, where the temperature is 27 °C, has a volume of 2.00 L. What would its volume be (a) in a hot room where the temperature is 47 °C, and (b) outdoors, where the temperature is –23 ºC? (Assume no change in pressure in either case.)
EXAMPLE 6.15 Charles’s Law: Temperature-Volume Relationships
Chapter 6 18
a. A sample of oxygen gas occupies a volume of 2.10 L at 25 °C. What volume will this sample occupy at 150 °C? (Assume no change in pressure.)
b. A sample of hydrogen occupies 692 L at 602 °C. If the pressure is held constant, what volume will the gas occupy after being cooled to 23 °C?
Exercise 6.15A
At what Celsius temperature will the initial volume of oxygen in Exercise 6.15A occupy 0.750 L? (Assume no change in pressure.)
Exercise 6.15B
EXAMPLE 6.15Charles’s Law: Temperature-Volume Relationships continued
Chapter 6 19
Ideal Gas Law
PV = nRT
• P = pressure
• V = volume
• n = number of moles
• R = gas constant = 0.0821 L atm/mol K
• T = absolute temperature
EXAMPLE 6.16 Ideal Gas Law
Use the ideal gas law to calculate (a) the volume occupied by 2.00 mol of nitrogen gas at 244 K and .9500 atm pressure, and (b) the pressure exerted by 0.500 mol of oxygen in a 15.0-L container at 303 K.
Determine (a) the pressure exerted by 0.0330 mol of oxygen in an 18.0-L container at 313 K, and (b) the volume occupied by 0.200 mol of nitrogen gas at 298 K and 0.980 atm.
Exercise 6.16A
Chapter 6 21
Determine the volume of nitrogen gas produced from the decomposition of 130 g sodium azide (about the amount in a typical automobile airbag) at 25 °C and 1 atm.
Exercise 6.16B
EXAMPLE 6.16 Ideal Gas Law continued