1. REGENTS CHEMISTRY
LETS REVIEW>>>>>> whispers from the past

2. Two hydrogen atoms form a hydrogen molecule when
REGENTS QUESTION
Two hydrogen atoms form a hydrogen molecule when
(1) one atom loses a valence electron to the other atom
(2) one atom shares four electrons with the other atom
(3) the two atoms collide and both atoms gain energy
(4) the two atoms collide with sufficient energy to form a bond

3. Which unit is used to express the pressure of a gas? (1) mole
REGENTS QUESTION
Which unit is used to express the pressure of a gas?
(1) mole
(2) kelvin
(3) joule
(4) pascal

4. REGENTS QUESTION
Which sample of matter sublimes at room temperature and standard pressure?
(1) Br2(ℓ)
(2) CO2(s)
(3) Cl2(g)
(4) SO2(aq)

5. REGENTS QUESTION Given the balanced equation representing a reaction:
H2 + energy → H+H
What occurs as bonds are broken in one mole of H2 molecules during this reaction?
(1) Energy is absorbed and one mole of unbonded hydrogen atoms is produced.
(2) Energy is absorbed and two moles of unbonded hydrogen atoms are produced.
(3) Energy is released and one mole of unbonded hydrogen atoms is produced.
(4) Energy is released and two moles of unbonded hydrogen atoms are produced.

6. Properties of Gases (Review)
No definite shape
No definite volume
compressible

7. The Behavior of Gases

8. Entropy is a measure of the (1) acidity of a sample
REGENTS QUESTION
Entropy is a measure of the
(1) acidity of a sample
(2) disorder of a system
(3) concentration of a solution
(4) chemical activity of an
element

9. Which element is a gas at STP? (1) sulfur (2) potassium
REGENTS QUESTION
Which element is a gas at STP?
(1) sulfur (2) potassium
(3) xenon (4) phosphorus

10. Which element is least likely to undergo a chemical reaction?
REGENTS QUESTION
Which element is least likely to undergo a chemical reaction?
(1) lithium
(2) fluorine
(3) carbon
(4) neon

11. Kinetic Molecular Theory
moving
molecules
well supported ideas

12. Basic Kinetic Theory of Gases
Composed of particles like atoms
(ex: He) or molecules like (O2 and CO2)
There are no attractive/repulsive forces.
Lots of empty space!!

13. Basic Kinetic Theory of Gases
2. Particles move in random, constant, straight-line motion.
Move independently of each other.

14. Basic Kinetic Theory of Gases
3. All collisions are elastic meaning that KE is transferred without loss of energy.
No change in kinetic energy.
Gases tend to diffuse towards areas of lower concentration.

15. REGENTS QUESTION
According to the kinetic molecular theory, which statement describes the particles of an ideal gas?
(1) The gas particles are arranged in a regular pattern.
(2) The force of attraction between the gas particles is strong.
(3) The gas particles are hard spheres in continuous circular motion.
(4) The collisions of the gas particles may result in the transfer of energy

16. REGENTS QUESTION:
Which statement describes particles of an ideal gas, based on the kinetic molecular theory?
(1) Gas particles are separated by distances smaller than the size of the gas particles.
(2) Gas particles do not transfer energy to each other when they collide.
(3) Gas particles have no attractive forces between them.
(4) Gas particles move in predictable, circular motion.

17. What is the gram formula mass of H2O? H 2 X 1= 2 O 1 X 16= 16
MENTAL PIT STOP
formula mass
What is the gram formula mass of H2O?
H 2 X 1= 2
O 1 X 16= 16
18 amu or g

18. What is the gram formula mass of LiF? Li 1 X 7= 7 F 1 X 19= 19
MENTAL PIT STOP
What is the gram formula mass of LiF?
Li 1 X 7= 7
F 1 X 19= 19
26 amu or g

19. Gas Pressure
Pressure- force exerted on container walls by particles in a gas
Units used- kPa, atm, Torr, mmHg
STP (Standard Temperature and Pressure) Table A
273 K or 0°C and
101.3 kPa = 1 atm = 760 Torr (mmHg)

20. Factors Affecting Pressure
Amount of Gas (number of moles)
Increasing amount will increase P (and vice versa)
Ex: bicycle tires, car tires
Temperature
Increasing temp. will increase P (and vice versa)
Ex: Tires deflate in winter
Volume
Decreasing volume will increase P, increasing volume decreases P
Ex: press down on a balloon and it pops

21. P1V1=P2V2
Pressure and volume have an inverse relationship, if temperature remains constant.
If volume is increased, pressure is decreased by the same factor.

22. Mathematically, the product of PV is constant or PV = k (where k is some constant).
Boyle’ Law
P1 V1 = P2 V2 = P3 V3…

23. Summary

24. GRAPH #1 REGENTS QUESTION
A rigid cylinder with a movable piston contains a sample of helium gas. The temperature of the gas is held constant as the piston is pulled outward. Which graph represents the relationship between the volume of the gas and the pressure of the gas?
GRAPH #1

26. Given the balanced equation representing a reaction:
MENTAL PIT STOP
Given the balanced equation representing a reaction:
2NO + O2 → 2NO energy
The mole ratio of NO to NO2 is
1 to (2) 3 to 2
(3 ) 2 to (4) 5 to 2

27. Determine the percent composition by mass of oxygen in the CaCO3.
MENTAL PIT STOP
Determine the percent composition
by mass of oxygen in the CaCO3.
Ca 1 X 40= 40
C 1 X 12=12
O 3 X 16 =48
48/100 X 100% = 48 %

28. Volume vs. Temperature V1/T1 =V2/T2
Volume and temperature have a direct relationship, if pressure is held constant.
If temperature (K) is increased, volume is increased by the same factor.

29. Mathematically, the relationship of volume divided by Kelvin temperature is constant or V/T = k.
Charles’ Law
V1 /T1 = V2 /T2 = V3 /T3 …

30. Summary

31. Pressure vs. Temperature P1/T1 =P2/T2
Pressure and temperature have a direct relationship, if volume remains constant.
If temperature (K) is increased, pressure will be increased by the same factor.

32. Mathematically, the relationship of volume divided by Kelvin temperature is constant or P/T = k.
Gay-Lussac’s Law
P1 /T1 = P2 /T2 = P3 /T3 …
Pressure

33. Pressure/Temperature relationship
Pressure increases, Temp. increases

34. Combined Gas Law Equation
P1 V1 = P2 V2
T T2

35. Which sample of matter is a mixture?
MENTAL PIT STOP
Which sample of matter is a mixture?
(1) Br2(ℓ) (2) KBr(s)
(3) K(s) (4) KBr(aq)

36. MENTAL PIT STOP
According to kinetic molecular theory, collisions between gas particles in a sample of an ideal gas
(1) increase the energy content of the gas sample
(2) produce strong attractive forces between the gas particles
(3) result in a net loss of energy by the gas sample
(4) transfer energy between the gas particles

37. Combined Gas Law Equation
Steps:
Determine which variable (if any) is kept constant.
Cancel those terms and remove them from the equation (Ex: If the question says that temperature remains constant the new equation becomes P1V1 = P2V2).
Plug in values that are given.
Solve for the unknown.
Be sure to always use temperature in Kelvins.

38. Ideal Gases vs. Real Gases
“Ideal gases” behave as predicted by Kinetic Molecular Theory.
Examples: H2 and He
Gases are most ideal at high temperature and low pressure (also have low mass and low polarity).

39. “Real gases” deviate from ideal behavior.
Why?
At low temps, gas particles become attracted to each other (KMT says they are not).
Under high pressure, gases occupy a specific volume (KMT says they don’t).

40. (1) low pressure and low temperature
REGENTS QUESTION
A sample of hydrogen gas will behave most like an ideal gas under the conditions of
(1) low pressure and low temperature
(2) low pressure and high temperature
(3) high pressure and low temperature
(4) high pressure and high temperature

41. Avogadro’s Law Avogadro’s number: 6.02 x 1023
Simply refers to the quantity of particles found in a mole.
At STP, 6.02 x 1023 particles of a gas occupies 22.4 L.
At STP, 3.01 x 1023 particles of a gas occupies 11.2 L.

42. Avogadro’s Law
Avogadro also hypothesized that equal volumes of different gases at the same temperature and pressure contain equal number of particles (or equal moles).

43. REGENTS QUESTION 6/2013 #60-62
Cylinder A has a movable piston and contains hydrogen gas. An identical cylinder, B, contains methane gas. The diagram below represents these cylinders and the conditions of pressure, volume, and temperature of the gas in each cylinder. *

44. *Compare the total number of gas molecules in cylinder A to the total number of gas molecules in cylinder B. [1] same volume means same number of molecules
State a change in temperature and a change in pressure that will cause the gas in cylinder A to behave more like an ideal gas. [1] high temperature low pressure
*In the space in your answer booklet, show a numerical setup for calculating the volume of the gas in cylinder B at STP. [1] (1.2) ( 1.25) = (1) (x)

45. MENTAL PIT STOP
Under which conditions of temperature and pressure does a real gas behave most like an ideal gas?
(1) 37 K and 1 atm
(2) 347 K and 1 atm
(3) 37 K and 8 atm
(4) 347 K and 8 atm

46. MENTAL PIT STOP
The diagram and data below represent a gas and the conditions of pressure, volume, and temperature of the gas in a rigid cylinder with a moveable piston.
Determine the volume of the gas in the cylinder at STP.
(1) (2.5) = (1) (x)
State one change in temperature and one change in pressure that will cause the gas in the cylinder to behave more like an ideal gas.
Temp higher than 298 K, Pressure lower than 1.0 atm

47. Vapor Pressure
In a sealed container, vapor pressure can be measured above a liquid.
Evaporation occurs when some particles from the surface of a liquid escape causing pressure to build up above the liquid (not to be confused with boiling).

48. Vapor pressure illustrated

49. Factors that Increase the Rate of Evaporation
Heating a liquid (not to boiling point)
Increasing surface area
Create air currents
(blow across the surface)

50. Liquid-Vapor Equilibrium
Some of the gas particles condense and then we find both evaporating and condensing occurs at the same rate.
Rate of Evaporation = Rate of Condensation

51. Related to Boiling
Boiling occurs when the vapor pressure becomes equal to the external pressure.
At normal atmospheric pressure, we call this normal boiling point.

52. Boiling and Attractive (Intermolecular Forces)
Boiling occurs when heat energy overcomes attractive forces between molecules.
The stronger the intermolecular forces, the higher the boiling point.
The weaker the intermolecular forces, the lower the boiling point.

53. Table H Notice, increasing temperature increases vapor pressure.
Line drawn at kPa corresponds to normal boiling point.

54. REGENTS QUESTION
Rubbing alcohol is a product available at most pharmacies and supermarkets. One rubbing alcohol solution contains 2-propanol and water. The boiling point of 2-propanol is 82.3°C at standard pressure.
Determine the vapor pressure of water at a temperature equal to the boiling point of the 2- propanol. [1]
>  Table H...a pressure between 48kPa and 52kPa