Intro to Biochemistry
Intermolecular Forces Homework
Due 1/15/2015
Intermolecular Forces
1.
a. Draw each bond dipole moment on the molecules shown
b. Write the order of increasing net dipole moment? (1-4)
CH3F
BrI
CH3Cl
CCl4
Br-I
2.
List the type(s) of intermolecular forces these molecules can have with water H2O
:
3. List all of the intermolecular forces that would occur in a liquid sample of the following substances (a-e)
a. H2O
b.
Neon
c.
C2H6O
d.
PH3
e. C2H6
4. Place the molecules in the above question in order of increasing boiling points (a-e)
5.
a. List the major intermolecular forces involved in each liquid substance given below
b. Place the substances in order of increasing boiling point (1-4)
6. Which molecule will have a larger boiling point: octane (C8H18) or pentane (C5H12) and why?
7. Draw two different ways ammonia (NH3) and water (H2O) can hydrogen bond to each other (showing each molecules
giving and then accepting Hydrogen)
______8
______9
______10
______11
______12
______13
______14
______15
______16
______17
Dipole-Dipole
Electrostatic
Hydrogen Bond
Intermolecular Forces
Intramolecular Forces
Ion-dipole force example
London-Dispersion
Polarizability
van der Waal's Force
Viscosity
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
The force acting between polar molecules
The resistance of a fluid to flow
The ease in changing electron distributions to induce a dipole
The weakest intermolecular force
Intermolecular forces that exclude charge-charge interactions
Requires the presence of N- O- or F-H bonds
The forces that act between molecules
The forces that hold atoms together to form molecules
Dissolving ionic compounds in water
Attractive interaction between oppositely charged ions
Thermochemistry (Entropy and Free Energy)
1. If the 2nd Law of thermodynamics says entropy must always increase, then how can solid ice form
from liquid water (which increases order)?
2. Bond disruption is associated with a negative ΔH and Bond formation is associated with a
positive ΔH. A) True
B) False
3. Which of these species would you expect to have the lowest standard entropy (S°)?
A) Br2(l)
B) Cl2(g)
C) F2(g)
D) H2(g)
E) I2(s)
4. Which of these species has the highest entropy (S°) at 25°C?
A) CH3OH(l) B) CO(g)
C) MgCO3(s) D) H2O(l)
E) Ni(s)
5. Arrange these processes according to increasing S.
1) H2O(g) H2O(l)
2) 2NO(g) N2(g) + O2(g)
3) MgCO3(s) MgO(s) + CO2(g)
6. The thermodynamic equation for Gibb's free energy, G = H - TS, combines two thermodynamic factors along
with available thermal energy (temp) to determine whether or not a reaction will be spontaneous.
Give a summary over each factor and what the three possible values (>, <, or = 0) of G denote.


H
S
G
7. With respect to the system only, a reaction with H > 0 and S < 0 is predicted to be:
A) Spontaneous at all temperatures
C) Spontaneous at low temperatures only
B) Spontaneous at high temperatures only
D) Nonspontaneous at all temperatures
8. Explain the significance of temperature in regards to thermodynamics and how it affects one of the factors in the
Gibbs equation.
9. Many biological reactions are thermodynamically unfavorable with positive H and negative S values. How then
does the body make these reactions go forward?
10. Polar solvents like water can dissolve small non-polar molecules by clathrate formation. Explain why
this is unfavorable and what normally occurs with larger non-polar molecules.