the Find following: 1) hybridization of each non-H atom 2) # of bonds 3) # of bonds sp3 sp sp H
sp2
N
N
O
2s & 2p
H
C H
C
H
5s & 1p
H
sp3
O
-2 sp2 sp3 O
H
C C
C
sp2
C C
H H
12s & 3p
C
sp2
O
3s & 1p
H
C
H
CHAPTER 7- STATES OF MATTER Three states: Molecular Speed Molecular Interaction Shape
Gas fast
low of container
Liquid medium
medium
Solid slow
high
bottom own shape of container
Condensed phases
Section 7.0
Pressure
barometermeasures atmospheric pressure
manometer-measures pressure of a gas in laboratory
Height in mm Hg 1 mm Hg = 1 torr
Converting between pressure units
1 atm (atmosphere) = 760 mm Hg = 760 torr 1 atm = 1.01105 Pa (pascal)
1 mm Hg = 1 torr Ex. 5.67 atm torr 5.67 atm 760 torr = 4,309 torr atm 1 atm = 0.0296 atm 760 mm Hg
Ex. 22.5 mm Hg atm 22.5 mm Hg
Ex. 22.5 mm Hg torr
22.5 mm Hg
1 torr = 22.5 torr 1 mm Hg
Section 7.1
Thermal Energy The average kinetic energy of the molecules in a system is the "thermal energy". thermal energy number
25 oC 50oC
speed/kinetic energy temperature, thermal energy molecules move faster!
Ethermal = ~RT = (8.3x10-3 KJ/molK)(T) Ex. Ethermal, 25C = (8.3x10-3 KJ/molK)(298 K) = 2.5 KJ/mol
Section 7.1
ABSOLUTE TEMPERATURE
Volume (L)
2 mol
1 mol 0.6 mol
32 212 F- Fahrenheit 0 100 C - Celsius 273 373 K - Kelvin
-273 -200 -100 "absolute 0 73 173
zero"
Temperature
water boils at 373 K and freezes at 273 K. No negative numbers! Use in calculations.
F = water boils at 212 and freezes at 32.
C = water boils at 100 and freezes at 0.
Converting between temperature units
K = C + 273.15
Ex. Room Temperature ~25 C K
25 C + 273.15 = 298.15 K
F = 9/5(C) + 32 C = 5/9(F - 32)
Ex. 79F C
5/9(79F - 32) = 5/9(47) = 26 C
Ex. -10C F 9/5(-10 C) + 32 = -18 + 32 = 14F
Section 7.1
GASES Gases adopt the shape and volume of a closed container. If the volume of the container is changed, the volume of the gas changes. Also the pressure increases!
V and P are "inversely proportional" Boyle's Law: PV = constant (if n and T are constant)
As volume , pressure
Section 7.1
1 P V
GASES
When a gas is heated, it expands. The molecules are moving faster and spread out more.
heat
cool As temperature , volume
T and V are "directly proportional"
Charles' Law: V/T = constant (n and P constant)
Section 7.1
GASES
Equal volumes of gases measured at the same temperature and pressure will contain the same number of molecules. n (# moles) V (volume) Avogadro's Law: n/V = constant (P and T constant)
n and V are As number of moles , volume "directly proportional"
Ex. 1 mol
Section 7.1
2 mol
THE IDEAL GAS LAW Put all the trends together: Boyle's Law: PV = constant (n and T constant) Charles' Law: V/T = constant (n and P constant) Avogadro's Law: n/V = constant (P and T constant)
PV/nT = constant The constant is R, the gas constant. R = 0.08206 (L atm/mol K)
PV = nRT
P in atm; V in L; T in K
Calculations with the Ideal Gas Law
Ex. Find P in torr if V = 3.2 L, n = 2.51 mol and T = 25C. P = nRT = (2.51 mol) 0.0821 Latm (273+25 K) V (3.2 L) mol K P = 19.9 atm 760 torr = 14,600 torr 1 atm
Ex. Find n in mol if V = 1.63 L, P = 1.5 atm and T = 29C.
n = PV = (1.5 atm) ( 1.63 L) = 0.0986 mol RT (0.0821 Latm/mol K) (273+29 K) If the gas is oxygen, O2, how many grams is this? 0.0986 mol (32 g O2/mol O2) = 3.16 g O2
Section 7.1
Mixtures of Gases
Dalton's Law- the total pressure is the sum of the pressures of the individual gases. Ptotal = Pi = P1 + P2 + P3 + ...
The individual pressures are called "partial pressures".
Section 7.1
So, in a mixture of N2, O2 and He, each gas has a partial pressure.
P PN 2 PO2 PHe Total
You can write the ideal gas law for each component of the mixture N2, O2 and He.
PN2V nN2 RT
PTotal nN 2
therefore
PN 2
nN 2 V
RT
nHe RT RT RT V V V
PN 2
PO2
PHe
nO2
Mixtures of gases are same throughout, or homogeneous Homogeneous mixtures are also called solutions Solutions are characterized by the concentrations of their components MOLAR CONCENTRATION (units of mol/L or mol L-1 or M)
nA Molar concentration of A [A] V
PTotal
nHe RT RT RT V V V
nN 2
nO2
Substituting molar concentrations into the above equation gives: Ptotal = [N2] RT + [O2] RT + [He] RT Ptotal =([N2]+[O2]+[He]) RT
Section 7.1
Calculations of Mixtures of Gases If 0.3 mol He and 0.6 mol of Ne are placed in a 2.0 L flask at 26C, what is the total pressure?
PTotal [ He]RT [ Ne ]RT ([He] [ Ne ]) RT PTotal (0.15M 0.3M ) (0.0821Latm / molK )(299K ) PTotal 11.04atm
Section 7.1
In-class practice: Calculate the Ptotal for a mixture with PHe = 0.78 atm, PO2 = 0.36 atm and PN2 = 0.02 atm. Ptotal = 0.78 + 0.36 + 0.02 = 1.16 atm
Calculate the volume and [CO2] if there is 44 g of CO2 at 25 C at 1 atm
44 g CO2 (mol/44 g) = 1 mol CO2 V = nRT = (1mol)(0.0821 Latm/molK)(298 K) = 24.47 L P (1 atm)
[CO2] = 1 mol/24.47 L = 0.041 mol/L
Intermolecular vs Intramolecular Forces Intermolecular forces are the forces between different molecules. Intramolecular forces are the forces within molecules.
Inter- holds different molecules together (weaker)
Intra- holds the molecule together (stronger)
Section 7.2
Intermolecular forces are more important in the condensed phases- liquids and solids.
Changes in State To change state (phase), a substance must make or break intermolecular forces.
Make intermolecular forces
Gas Liquid Solid freeze
condense
evaporate deposit sublime
melt
Break intermolecular forces
Section 7.5
Solid and Liquid Liquid freeze
Solid
At the melting/freezing point, the solid and the liquid coexist. Have equal rates of melting and freezing. "dynamic equilibrium" liquid solid
Add heat to break intermolecular forces. Heat of fusion (Hfus) - heat required to melt a substance.
Section 7.5.1
Heat of Fusion temperature liquid
solid
Hfus sl
heat added
Heat of fusion is heat needed to break intermolecular forces and make the solid a liquid.
No temperature change while this happens!
Section 7.5.1
Pressure Changes Pressure can also be used to change state but it takes a large pressure change.
Most substances, solid is more dense. Exception- WATER!
Solid more dense than liquid (most substances)
Liquid more dense than solid (water)
pressure
liquid
pressure
solid
liquid solid
temperature
temperature P liquid solid T solid liquid
P gas liquid T gas liquid
Liquid and Gas Gas Liquid
condense
At condensing/evaporation the point, the liquid and the gas coexist. Have equal rates of condensing and evaporation.
"dynamic equilibrium"
gas
liquid
Add heat to break remaining intermolecular forces. Heat of vaporization (Hvap) - heat required to evaporate a substance.
Heat of Vaporization gas
temperature
liquid
Hvap lg
heat added
Heat of vaporization is heat needed to break the remaining intermolecular forces and make the liquid a gas.
No temperature change while this happens!
All IM forces broken
temperature
gas
liquid
Hvap lg heat added
Vapor Pressure Vapor Pressure- the pressure of the gas when the liquid and vapor are in equilibrium at a given temperature. Pvapor T
Pvapor
liquid
liquid
temperature vapor pressure (more molecules escaping into vapor phase!) intermolecular forces vapor pressure (less molecules escaping into vapor phase!)
Boiling Point
Boiling Point- the temperature at which the vapor pressure equals the external pressure. pressure BP (ex. Water boils at 95 C in Denver) pressure BP (ex. Pressure cooker- use water to cook at >100 C ) intermolecular forces boiling point (harder to make molecules escape into vapor phase!)
In cartoon form:
Low pressure = easy escape from liquid phase
Molecules of the atmosphere (N2, O2, CO)
High pressure = difficult escape from liquid phase
Molecules of the liquid
Solid and Gas Gas deposit Solid
Sometimes the solid and the gas can coexist (no liquid!). Have equal rates of deposition and sublimation.
"dynamic equilibrium"
gas solid
Add heat to break intermolecular forces. Heat of sublimation (Hsub) - heat required to sublimate a substance.
Sublimation
pressure
solid gas temperature
P solid T gas
When you can "smell" a solid, it is subliming. You smell the gas phase molecules. Ex. Moth balls (naphthalene)
intermolecular forces sublimation (harder to make molecules escape into vapor phase!)
Phase Diagrams Put all of the transition diagrams together into one. WATER
Pressure (atm)
liquid solid gas triple pointall three phases in equilibrium
Temperature (C)
Using a phase diagram, you can predict the phase that will be present at any pressure/temperature combination.
Section 7.5.4
Phase Diagrams Can predict the boiling and freezing points at a given pressure. WATER
Pressure (atm)
1
solid
liquid
gas
normal freezing point
0
100
Temperature (C)
"normal" means at 1 atm
normal boiling point
Section 7.5.4
Phase Diagrams Can predict phase changes due to changes in temperature and pressure.
WATER
Pressure (atm)
A
solid
B
liquid D C
gas
Temperature (C) AB: Temperature- solid to liquid C D: Pressure- gas to liquid
Section 7.5.4
Intermolecular Forces Consider 3 types of intermolecular forces:
Occur in molecules containing
Dispersion Forces temporary dipoles (ALL molecules!) permanent dipoles H bound to N, O or F
Strength of forces
Weak
Dipole-Dipole Forces
Hydrogen Bonding
Medium Strong
Section 7.2
Dispersion Forces Induced Dipole- positive and negative regions in molecules caused by random electron motion.
neutral molecules
e randomly collect on one side and cause a dipole
e e
+ +
e e
induces a dipole in next molecule over
+
e e
Dispersion Force- the force of attraction between oppositely charged parts of atoms due to induced dipoles Can happen in ANY molecule. dispersion forces in larger molecules ( MW)
Dipole-Dipole Forces Permanent Dipole- a permanent asymmetric charge distribution.
+
H - Cl
+
H - Cl
+
H - Cl
Molecules with a permanent dipole are called "polar". The permanent dipoles align and are attracted to each other. dipole-dipole forces
Section 7.2.2
Dipole-Dipole Forces
Consider the polarity of each individual bond.
Sum is the net dipole!
Net dipole
H H
O
H H
O
O Water molecules will align according to the dipole.
H H
O
H H
Dipole Moments
H H
N
H
Net dipole
Ammonia is a polar molecule
Dipole Moments -Although individual bonds may have dipoles, the symmetrical arrangement of the atoms around the central atom cancels those dipoles and the molecule is non-polar.
O = C =O
CO2 is linear so the sum of the dipoles equals zero. Non-polar
Determining net dipole F B F trigonal planar
F The three F atoms are arranged symmetrically around the B, therefore the dipole moments cancel. Non-polar
F
Cl
B F
Although the 3 atoms are arranged symmetrically, they are not all the same. Polar
Determining net dipoles Cl
Cl Cl
Cl tetrahedral H
The 4 Cl atoms are arranged symmetrically around the C atom. Non-polar
H Cl
Cl
Although all 4 atoms are arranged symmetrically, they are not the same. Polar
H H
C C
F C C F
Determining net dipoles
C C
H
H
Dipoles are in equal and opposite directions and therefore cancel out. Non-polar
H H
C
C
H C C F
C C
F
H
F atoms are not arranged symetrically about the ring therefore there is a net dipole. Polar
6-membered ring is planar
Determining net dipoles
Cl Cl Cl
S
Cl
Cl Cl
All atoms are arranged symmetrically around the S therefore the dipole moments cancel. Non-polar
Cl
Cl Cl
S Cl
F F
Atoms are arranged symmetrically, however all the atoms are not the same. Polar
octahedral geometry
Hydrogen Bonding Occurs only in compounds with H-O, H-N and H-F bonds. The large EN difference between H and O, N or F leads to large partial charges on the atoms Result is a strong attraction between oppositely charged ends of two adjacent molecules
O
H H
hydrogen bond
O
H
O
H
H
H
Hydrogen bonding is VERY strong and causes BP's
Intermolecular Forces- Flow Chart Is the molecule polar?
no Nonpolar molecule dispersion forces only no
Polar molecule dispersion dipole-dipole
Section 7.2
yes Is there a H bound directly to a N, O or F?
yes
Polar molecule dispersion dipole-dipole hydrogen bonding
Which substance has the higher boiling point, A or B? H-bonding > dipole-dipole > dispersion
decreasing boiling point, decreasing strength of interaction
If both substances have dispersion and dipole-dipole interactions: if dispersion forces are similar (A and B have similar Mm) than the more polar substance will have higher bp if polarity is similar then the substance with the higher Mm will have the higher bp (more common situation) Ex. HCl and HI Polarity is similar so HI has higher boiling point due to stronger dispersion forces
Ch 7 Practice Problems
7, 9, 11, 13, 15, 25, 27, 29, 33, 35, 37, 39, 41, 43, 45, 49, 51