1. Unit 6: Part B PHYSICAL Behavior of Gases

2. X. Endothermic and exothermic (revisited)
Energy is either absorbed or released in chemical reactions
Remember:
- Breaking bonds is ____________________
- Heat is ___________ the reaction from the surroundings
- Ex) heat + Br2  Br + Br
- Creating bonds is _________________
- Ex) N+ N N2+ energy
ENDOTHERMIC
ENTERING
EXOTHERMIC
EXITING

3. X. Endothermic and exothermic (revisited)
Where does the heat come from (or go to)? ______________________
For exothermic reactions, heat (energy) leaves the reaction and moves __________________________. Therefore, making the surrounding temperature _________________
Exothermic Chemical Equation:
The surroundings
into the surroundings
warmer
Reactant(s)  Product(s) + HEAT

4. X. Endothermic and exothermic (revisited)
For endothermic reactions, heat (energy) leaves the surroundings and moves __________________________. Therefore, making the surrounding temperature _________________
Endothermic Chemical Equation:
Into the reaction
colder
Reactant(s) + HEAT  Product(s)
ENDOTHERMIC REACTION VIDEO

5. X. Endothermic and exothermic (revisited)
DISORDER
Entropy: Degree of ___________________ in a system
Entropy Increases, if
1) _________________________________________________
2) __________________________________________________
3) __________________________________________________
Substance goes from a s  l  g
More moles of gas are produced
Large molecule breaks up

6. X. Endothermic and exothermic (revisited)
Enthalpy: It is a measure of the heat released or absorbed in a reaction. If heat is released then the reaction is an exothermic reaction, heat will be on the products side and the ΔH will be negative. If heat is absorbed then the reaction is an endothermic reaction, heat will appear on the reactants side and the ΔH will be positive. (see Table ____ on Reference Tables).
Examples: Tell whether each of the following reactions are endothermic or exothermic (you may have to use table I). Then tell whether the temperature of the surroundings increases or decreases as a result.
Entropy Endo/Exothermic _______Surroundings
_____________________C6H12O O2  6CO H2O + heat _________ I
warmer ↑
Exo (-∆H)

7. X. Endothermic and exothermic (revisited)
Entropy Endo/Exothermic _______Surroundings
1. ___________________C6H12O6 (s) + 6O2(g)  6CO2 (g) + 6H2O (l)+ heat ____________
2. _________________ 2H2O kJ  2H2 (g) + O2 (g) __________
3. ____________________ N2 (g) + 3H2 (g)  2NH3 (g) ________
4. ______________________  NaOH(s)  Na+ (aq) + OH- (aq) _________
5. _____________________ C2H5OH(l) + 3O2 (g)  2CO2 (g) H2O(l) _____
6. ________________________2KClO3(s)  2KCl(s) + O2(g) + heat ________
7. ______________ _______H+(aq) + C2H3O2(aq) + heat  HC2H3O2(l) ______

8. XI. Kinetic Molecular Theory
DO NOT ACTUALLY EXIST
 Ideal Gas: A set of gases that ________________________________, but represents a standard that we can use to predict the behavior of gases.
Kinetic Molecular Theory of Ideal Gases tell how ideal gases behave:
1 . 2. 3. 4. 5.
 However, Real gases behave ideally under ________________ temperature and  ____________ pressure
Particles are small and spread far apart
Travel in constant, random, straight line motion
Can not happen in
real-world
Have no attractive forces (IMF’s)
Don’t lose energy when they collide, but they can transfer energy in the collision
Move faster when hotter
HIGH
LOW

9. XII. Vapor Pressure ______ VP = _________________________ Example:
______ VP = _________________________ Example:
Factors for Vapor Pressure 1. 2.
Pressure a liquid “feels” pushing it to evaporate (turn to gas)
HIGH
Evaporates easily
Ethanol has higher VP than H2O, so it evaporates more easily
Strength of intermolecular force: molecules held together by dipole-dipole (polar) have lower VP than Van der Waals (nonpolar)
(H2O does not evaporate as fast as methane (CH4))
Temperature/Pressure: increase temp., increase VP

10. XII. Vapor Pressure Vapor Pressure of Four Liquids (See Table _____)
Questions:
1. What is the vapor pressure of propanone at 35 oC? _______
2. What temperature does water boil at if the pressure is 70 kPa? ______
3. What is the normal boiling point of ethanoic acid? __________
Sublimation:
Example: “Dry Ice” CO2 (s)  CO2 (g) H
Measured in: kPa (101.3 kPa = 1 atm = 760 mmHg = 760 torr.)
48 kPa
90 degrees C
117 degrees C
Occurs because solids have very weak IMF (usually Van de Waals).
They go directly from s  g and have HIGH VP

11. Check for Understanding
How could you change the boiling point temperature of a substance without adding anything to the substance?
You spill a glass of water on the floor. How could you get the water to evaporate faster, without using a mop or something to soak it up?
Change your altitude (increase/decrease altitude (lower/higher pressure), lower/higher boiling point)
Increase/decrease the temperature of the room.
(increase/decrease surface area).

12. XIII. Evaporation vs. Boiling Point
Converting l  g at the surface of a liquid that is NOT BOILING (leaving clothing out to dry)
When the vapor pressure of liquid
= air pressure
Temperature when a liquid boils at standard pressure
(101.3 kPa or 1 atm = sea level)
Water = 100oC
1. Substance (strong IMF, slower evaporation)
2. Temperature (high temp., faster evaporation)
3. Surface area (increase, faster evaporation)
Water Boiling at 70.0oC Video

13. Check for Understanding
You move to Denver, CO, where the altitude is 5,183 feet above sea level (mile high city – approximately).
What would this high altitude due to the spacing of air particles?
Based on your answer to question 1, what would this do to the vapor pressure of water?
Based on your answer to question 2, what would this do to the boiling point temperature of water in Denver?
The air pressure would be lower/higher, so the particles would be more/less spread out.
The vapor pressure would be more/less (more/less pressure pushing on the water – approximately 90 kPa in Denver)
Boiling temperature would be higher/lower

14. XIV. Gas Laws A. Pressure and Volume (Boyle’s Law)
A. Pressure and Volume (Boyle’s Law)
As pressure _______________, volume ________________, and _____________ is constant
 Volume Relationship:
Pressure
increases
decreases
temperature
inverse
Equation: P1V1 = P2V2
Question: If the pressure on a gas is halved, under constant temperature, what will happen to the volume of the gas?
The volume will double

15. Think about this
You blow up a balloon and it expands each time you exhale into the balloon.
What happens to the number of gas particles you put in the balloon each exhale?
2. What happens to the pressure on the balloon?
It increases/decreases (more/less gas particles pushing against the wall of the balloon)
3. What is the relationship between gas particles and pressure
More/less gas particles, more/less pressure

16. XIV. Gas Laws B. Pressure and Number of Gas Particles
B. Pressure and Number of Gas Particles
As number of gas particles _______________, pressure ________________
 Pressure Relationship:
# of Gas Particles
increases
increases
Direct
Question: If the number of particles of a gas is tripled, under constant volume, what will happen to the pressure on the gas?
The pressure will triple

17. Think about this
You blow up a balloon inside the school and bring it outside (it is – 10oC out).
What would you see happen to the balloon as you stand outside?
The balloon would get bigger/smaller
2. Why would this occur?
The cold air would cool the gas inside, bringing the molecules farther/closer together
3. What would you see happen once you brought it back inside? Why?
It would expand/shrink. Warm air would warm the gas inside, causes the molecules to spread out (volume increases).

18. XIV. Gas Laws C. Temperature and Volume (Charles’s Law)
C. Temperature and Volume (Charles’s Law)
As temperature_______________, volume ________________ and ______________ is constant
 Volume Relationship:
Temperature
increases
increases
pressure
Direct
Equation: V 1 = V 2
T1 T2
Question: If the temperature of a gas is halved, under constant pressure, what will happen to the volume of the gas?
The volume will be halved

19. Think about this: Pressure and Temperature of A Gas
On cold days the sensor in my car says that my tires have lower than normal pressure.
Why would this happen?
The cold air makes the gas particles inside the tire slow down/speed up causing the tire pressure to be more/less
2. What two properties and being compared?
3. What is the relationship between these two properties
As temperature increases, pressure
Video Demonstration

20. XIV. Gas Laws D. Temperature and Pressure (Gay-Lussac’s Law)
D. Temperature and Pressure (Gay-Lussac’s Law)
As temperature_______________, pressure________________ and ______________ is constant
 Pressure Relationship:
Temperature
increases
increases
volume
Direct
Equation: P 1 = P 2
T1 T2
Question: If the temperature of a gas is tripled, under constant volume, what will happen to the pressure of the gas?
The pressure will triple

21. XV. Combined Gas Law Equation (See Table _____)
  The relationships among pressure, temperature, and volume can be mathematically represented by an equation known as the combined gas law.
Equation (See Table _____)
Important notes when using the equation: T
P 1 V1 = P 2 V2
T T2
1. Temperature must be in Kelvin, NOT Celsius
2. For pressure and volume, make sure the units of the initial and final are the same
3. If a variable remains constant, you can take it out of the equation

22. XV. Combined Gas Law
1. The pressure of a gas at 200. K is increased from 200. kPa to 305. kPa at a constant volume. What is the new temperature?
2. If a gas at 8.00 atm is cooled from 600. K to 150. K in a rigid container, what is the final pressure?
305 K
2.00 atm

23. XV. Combined Gas Law
3. If I have 2.90 L of gas at a pressure of 5.00 atm and a temperature of 320. K, what will be the temperature of the gas if I decrease the volume of the gas to 2.40 L and decrease the pressure to 3.00 atm?
4. If I initially have a gas at a pressure of 12 atm, a volume of 23 liters, and a temperature of 250 K, and then I raise the pressure to 14 atm and increase the temperature to 350 K, what is the new volume of the gas?
159 K
28 L