GChem: Bonding and Intermolecular Forces and Thermodynamics Flashcards

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1
Q

The more S character the _____ shorter/longer the bond

A

The shorter the bond (stronger the bond)

BUT only when comparing the same types of bonds (ex. compare C-O bonds to each other)

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2
Q

Coordinate covalent bond and body example

A

B/w atoms with lone pair and e- deficient species (lewis acid/electrophile)
Lewis acids: B, (transition) metal cation, BF3 = lewis acid b/c wanted a complete octet
When one atom donates BOTH of the shared e- in the bond
Between lewis base/ligand/nuecleophile and lewis acid/electrophile
A lewis base is a molecule or ion that donates a pair of nonbonding electrons so it must have them in the first place
Ex. In hemoglobin, ligand chelate and O2 binds Fe2+
BH4- CANNOT behave like lewis base

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3
Q

Ionic bonds - the strength of the bond is proportional to… and decrease as ions get closer/farther apart

A

The strength of the bond is proportional to the charges of the ions and decrease as ions get farther apart
Ex. MgS vs NaCl
MgS - Mg2+ S2-
NaCl - Na1- Cl1-
so MgS “bond” expected to be four times stronger than NaCl bond

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4
Q

Orbital geometry/molecular geometry (state bond angle for each) vs shape of molecule

A

Orbital geometry/molecular geometry = linear (180º), trigonal planar (120º), or tetrahedral (109.5º)

Shape: bent, trigonal pyramidal

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5
Q

How many sigma and pi bonds are in a triple bond?

A

one sigma, two pi

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6
Q

List the strengths of IMFs - there are 5

A
H-bonds
Ion-dipole
dipole-dipole
dipole -induced dipole 
london dispersion
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7
Q

For IMFs, a _____ more/less polar molecule generates a stronger force and a molecule with ______ more/less e- and ____ larger/smaller size generates a stronger force bc it’s _____ more/less polarized

A

Pretty sure the polarized rule works for all IMFs
more
more
larger
more
Ex. F2 and Cl2 exist as gases and but Br2 is liquid and I2 is solid bc strength of dispersion forces increase as atomic size increases.

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8
Q

In order to have a hydrogen bonding, you need…

A

Bond between H and N,O, or F and another molecule must have a lone pair of e-s on an N,O, or F atom.
Ex. water to other waters

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9
Q
Substances with stronger IMF have:
\_\_\_\_bp
\_\_\_\_mp
\_\_\_\_viscosities
\_\_\_\_vapor pressure
A

greater bp and mp
greater viscosity
lower vapor pressure (more easily it evaporates and liquids with high vapor pressures are volatile)

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10
Q

*Ionic Solids

What 2 factors influence its strength?

A

Electrostatic attraction between cations and anions in a lattice structure (most solid at room temp)
The intermolecular bonds are the same as the intramolecular bonds! All ionic
Magnitude of ion charges (biggest effect)
Size (the smaller the ions, the more attracted to each other)

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11
Q

(I skipped)

Network Solids

A

Connected in lattice of covalent bonds - super strong
tend to be hard solids at room temp
Ex. diamond and quartz

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12
Q

Metallic solids

conduction electrons

A

A sample of metal can be thought of as a covalently bound lattice of nuclei and their inner shell electrons surrounded by sea/cloud of electrons Freely moving electrons called conduction electrons
SO EXCELLENT CONDUCTORS OF ELECTRICITY, MALLEABLE, DUCTILE
Almost all solid at room temp
vary in strength

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13
Q

I skipped

Molecular solids

A

Particles at the lattice points of crystals of molecular solid are molecules held together by one of three types of intermolecular interactions - hydrogen bonds, dipole-dipole forces, or london dispersion so typically has lower mp and bp
often liquids and gases at room temp and start to be more solid as strength of their intermolecular forces increase

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14
Q
Rank the following from highest to lowest bp:
I  H2SO4
II NH3
III CO2
IV H20

I>IV>II>III
II>I>IV>III
I>III>IV>II
IV>III>I>II

A

A is the answer
I and IV are liquids at room temp and II and III are already gases!

H2SO4 and H20 have hydrogen bonding but H2SO4 is larger (can have greater polarity) and more sites to accept H-bonds from surrounding molecules

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15
Q

When energy flows into a system from the surroundings, the energy of the system _____ increases/decreases and the energy of the surroundings ____increases/decreases

A

increases

decreases

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16
Q

Enthalpy

What is the sign when a bond is formed? When broken?

A

heat energy that is releases or absorbed when bonds are broken and formed during a reaction that’s run at constant pressure. The symbol is H
When a bond is formed, energy is released ∆H<0 (heat flow out of the system
Energy must be put into a bond in order to break it ∆H>0 (heat flows into the system)

17
Q

Heat of reaction

A

Enthalpy change ∆H

18
Q

How much heat is produced when 16 g of oxygen gas reacts with excess methanol?
2CH3OH + 3O2 -> 2CO2 + 4H2O ∆H = -1352 kJ

A

First have to convert 16g of O2 to moles BUT for moles calculation must remember to do 16g/2(16) have to multiply 16 by 2 bc have to do this when see subscript
then continue with calc
solution page 125 of GChem
225kJ

19
Q

Standard conditions vs standard temperature and pressure (STP)

A

Standard conditions (like room temp) are 298ºF/25ºC, 1 M solution, 1 atm

STP - 0ºC
1 atm (pressure)
1 mole of gas will take up 22.4 L of the volume of the container.

20
Q

Equation for heat of formation

A

∆Hºrxn = (Σn × ∆Hºf,products) -

Σn × ∆Hºf,reactants

21
Q

∆Hºf is 0 for elements in their natural state -> natural phase and diatomic at standard conditions
Name diatomic elements and phase at standard temp

A
Have Hydrogen (gas)
No     Nitrogen (gas)
Fear  Fluorine  (gas) 
Of      Oxygen  (gas)
Ice     Iodine (gas) 
Cold  Chlorine (gas)
Beer  Bromine  (LIQUID)
22
Q

Hess’s Law 2 things to remember when adding enthalpies up

A

Basically add two chemical equations to get the right one
If a rxn is reverse, sign of ∆H is reversed
If an equation is multiplied by a coefficient, then ∆H must be multiplied by that same value

23
Q

Equation for ∆Hrxn? (third reaction)

A

∆Hrxn = Σ(BDE bonds broken) - Σ(BDE bonds bonds formed)
so if stronger bonds are being formed than those being broken, then ∆Hrxn will be neg - more E is released than supplied and rxn is exothermic

24
Q

Equation for ∆Hrxn? (third reaction)

A

BDG -> bond dissociation energy
∆Hrxn = Σ(BDE bonds broken) - Σ(BDE bonds bonds formed)
so if stronger bonds are being formed than those being broken, then ∆Hrxn will be neg - more E is released than supplied and rxn is exothermic

25
Q

∆S =

What factors influence ∆S?

A

∆S = Sproduct - Sreactants
In terms of who has more entropy:
Gases>Liquids>solids
Particles in solution have more entropy than undissolved solids
Two moles of substance have more entropy than one mole
The value of ∆S for a reverse rxn has the same

26
Q

Equation for ∆G

What does it mean when ∆G is pos, 0, neg?

A

∆G = ∆H -T∆S
pos -> nonspontaneous
0 -> at equilibrium
neg -> spontaneous

27
Q

The differencen between exothermic/endothermic vs exergonic/endergonic

A

exothermic/endothermic for ∆H

exergonic/endergonic for ∆G and when looking at graphs to see if prod are lower than reactants etc

28
Q

Ea

A

Ea is the extra E the reactants required to overcome the activation barrier, and determines the kinetics of the reaction
The higher the barrier, the slower the reaction proceeds to equilibrium

29
Q

What happens to ∆G, ∆H, and ∆S for the reverse rxn?

A

Same magnitude, opposite sign

30
Q

Heat(enthalpy) of vaporization

A

Heat to evoke evaporation phase change

31
Q

sublime

A

convert a solid to a vapor

32
Q

Heat of fusion?

A

When a solid undergoes melting or freezing

Conversion between liquid and solid

33
Q

What is greater, the heat of fusion or heat of vaporization?

A

For all substances, the heat of vaporization is substantially higher than the heat of fusion. Much more energy is required to change the state from a liquid to a gas than from a solid to a liquid.

34
Q

*What are units for mass of a solvent? (technically two different units mean the same thing)

A

1 mL = 1 g

35
Q

Amphiphilic (amphiphatic)

A

A molecule having both hydrophobic (nonpolar) and hydrophilic (polar) regions

36
Q

Urea -> what does it do?

A

Based on its structure, urea, CO(NH2)2, will interact with the polar moieties of a protein via hydrogen bonding, which include the peptide backbone and polar residues (charged or uncharged). By disabling intramolecular hydrogen bonding urea is capable of stabilizing the denatured state of a protein