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Spring 2018 > chem170 ch9, 10, 11 > Flashcards

chem170 ch9, 10, 11 Flashcards

1
Q

Use the bond energies provided to estimate ΔH°rxn for the reaction below.

C2H4(g) + H2(g) → C2H6(g) ΔH°rxn = ?

Bond Bond Energy (kJ/mol)

C-C 347

C-H 414

C=C 611

C≡C 837

H-H 436

A

To determine the heat of reaction, subtract the total bond energy of the reactants from the bond energy of the product.

C2H4 is ethene. If you go to the website below, you can see the structure of this molecule.
http://en.wikipedia.org/wiki/Ethylene

It has 1 C=C and 4 C-H’s.
Total bond energy = 611 + 4 * 414 = 2267 kJ/mol

H2 = 436 kJ/mol
Total bond energy = 2703 kJ/mol

C2H6 is ethane.
If you go to the website below, you can see the structure of this molecule.
http://en.wikipedia.org/wiki/Ethane

It has 1 C-C and 6 C-H’s.
Bond energy = 347 + 6 * 414 = 2831 kJ/mol
Heat of reaction = 2831 – 2703 = 128 kJ/mol

If you go to the website below, you will see examples of this type of problem. As I look at this method, I realize that I worked this problem backwards. For C2H4 and H2 to react, the bonds must be broken. This requires 2703 kJ/mol of energy. As C2H6 is formed, bonds are made. As this happens 2831 kJ/mol of energy is released. To determine the heat of reaction, subtract the bond energy of the product from the sum of the bond energies of the reactants. The only difference is that the heat of reaction is negative instead of positive.

http://www.kentchemistry.com/links/Kinet…
ΔH°rxn = -128 kJ/mol

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2
Q

What is the formal charge of the C on CCl3+1 ?

A

+1

FC= element - bonds
FC= C(4e'-) - 3 (CL bonds)
FC= 1
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3
Q

Which of the following represents the Lewis structure for S (2⁻)?

A

S w/ 8 electrons

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4
Q

Give the number of valence electrons for ICl5.

A

42

cl(5)7=35
I(1)7=7
T=42

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5
Q 
Identify the compound with atoms that have an incomplete octet.
A) ICl5
B) CO2
C) BF3
D) Cl2
E) CO
A

BF3

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6
Q

Place the following elements in order of decreasing electronegativity.

        C         F          Sn
A

Selected Answer:
Correct
F > C > Sn

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7
Q

Identify the weakest bond.

single covalent bond
double covalent bond
Triple covalent bond

A

single covalent bond

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8
Q

Using periodic trends, place the following bonds in order of increasing ionic character.

       Si-P      Si-Cl     Si-S
A

Selected Answer:
Correct
Si-P < Si-S < Si-Cl

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9
Q

Choose the best Lewis structure for CH2Cl2.

A

single bonds with C in the center, 6 valence on each CL

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10
Q

Place the following in order of decreasing magnitude of lattice energy.

       NaF      RbBr     KCl
A

Selected Answer:
Correct
NaF > KCl > RbBr

The following two factors are important in determining the magnitude of the lattice energy.

1) The smaller the distance between the nuclei of the ions the greater is the attractive force.
2) The charge of the ions also is a factor, the greater the charge the greater is
the attractive force.

In this case all cations have the same charge and all the anions have the same charge.

RbBr largest cation and largest anion.
NaF smallest cation and smallest anion

Greatest lattice energy NaF > KCl > RbBr least

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11
Q

What is the molecular geometry of a molecule with 2 outer atoms and 2 lone pairs on the central atom?
What is its geometry?

A

Bent
(Think of the electron geometry 1st, then subtract the lone pairs to get the molecular geometry)

tetrahedral
The steric number is 4 because 2 outer atoms + 2 lone pairs = 4 regions of high electron density.

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12
Q

What is the molecular geometry of a molecule with 5 outer atoms and 1 lone pair on the central atom?

What is the electronic geometry of this molecule?

A

octahedral

The steric number is 6 because 5 outer atoms + 1 lone pair = 6 regions of high electron density.

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13
Q

What is the molecular geometry of PCl3?

What is the electronic geometry of PCl3?

A

trigonal pyramidal

Tetrahedral
3 groups + 1 lone pair

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14
Q

What is the molecular geometry of SCl2?

What is the electronic geometry of SCl2?

A

bent

tetrahedral
2 bonds 2 lone pairs

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15
Q

What is the value of the bond angles in SiH4?

How many electron regions are there around the central atom in SiH4?

Determine the electronic geometry

A

109.5*
For the molecules in which there are no lone pairs of electrons on the central atom the electronic geometry is the same as the molecular geometry. The molecular geometry of a molecule describes the three-dimensional shape of just the atoms.

How many electron regions are there around the central atom in SiH4?
4

Determine the electronic geometry
tetrahedral

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16
Q

What is the value of the smallest bond angle in XeF4?

What is the electronic geometry of this molecule?

What is the molecular geometry of this molecule?

A

90 degrees
For the molecules in which there are two lone pairs of electrons on the central atom the electronic geometry is different than the molecular geometry. The molecular geometry of a molecule describes the three-dimensional shape of just the atoms.

What is the electronic geometry of this molecule?
octahedral

What is the molecular geometry of this molecule?
square planar

17
Q

What is the value of the bond angles in BF3?

A

120 degrees
For the molecules in which there are no lone pairs of electrons on the central atom the electronic geometry is the same as the molecular geometry. The molecular geometry of a molecule describes the three-dimensional shape of just the atoms.

18
Q

What is the value of the bond angle in I3−?

A

180 degrees
For the molecules in which there are three lone pairs of electrons on the central atom the electronic geometry is different than the molecular geometry. The molecular geometry of a molecule describes the three-dimensional shape of just the atoms.

19
Q

What type of hybridization is exhibited by the central atom in CHClO?

A 
Relation between charge clouds and hybridization
Once the number of charge clouds around the central atom is determined, the hybridization can be specified by using the following table:
Clouds	Hybridization
2	sp linear
3	sp2 trigonal planar
4	sp3 tetrahedral
5	sp3d trigonal bipyramidau
6	sp3d2 octahedral
20
Q

Determine the electron geometry (eg) and molecular geometry (mg) of the underlined carbon in CH3F.

A

eg = tetrahedral, mg = tetrahedral

h3-c-f == 4 sides duh

21
Q

The bond angle in NBr3 is:

A

107°

22
Q

Describe a pi bond.

A

side to side overlap of p orbitals

23
Q

Give the hybridization for the C in HCN.

A

sp

24
Q

Give the approximate bond angle for a molecule with a tetrahedral shape.

A

109.5°

25
Q

A molecule containing a central atom with sp3d2 hybridization has a/(an) ________ electron geometry.

A

octahedral

26
Q

Identify the number of electron groups around a molecule with sp2 hybridization.

A

3

27
Q

Using the VSEPR model, the electron-domain geometry of the central atom in NO3- is

A

trigonal planar.

28
Q

How many sigma and pi bonds does contain the molecule CH2CHCH3?

A

8 sigma, 1 pi

double bonds = p

CH2CH-C = sp2

29
Q

Which molecule is polar?

A

SF2

30
Q

Calculate the total quantity of heat required to convert 25.0 g of liquid CCl4(l) from 30.0°C to gaseous CCl4 at 76.8°C (the normal boiling point for CCl4). The specific heat of CCl4(l) is 0.857 J/(g ∙ °C), its heat of fusion is 3.27 kJ/mol, and its heat of vaporization is 29.82 kJ/mol.

  1. 38 kJ
  2. 53 kJ
  3. 85 kJ
  4. 00 kJ
A

This question has two parts. First you have to figure out the amount of heat needed to get it to the boiliing point, and then calculate the heat to change it from liquid to gas at the bp.

25.0g(0.857J/gºC)(76.8-30ºC)= 1002.69J
change to kJ: 1.00269KJ

Since your vaporization heat is in kJ/mol, you have to figure out how many moles you have.
Molar mass of CCl4 is 12.00+4(35.453)=12.00+141.8= 153.8g/mol
You have 25.0g(1mole/153.8g)= 0.1625 moles
Heat to vaporize= 0.1625moles(29.82kJ/mole)= 4.85 kJ
Add this to heat needed to raise to bp:
4.85kJ + 1.00269kJ= 5.85264kJ

31
Q

A molecule contains hydrogen bonding if it contains hydrogen covalently bonded to

A

fluorine, oxygen, or nitrogen.

32
Q

The heat of vaporization of water at 100°C is 40.66 kJ/mol. Calculate the quantity of heat that is absorbed/released when 6.00 g of steam condenses to liquid water at 100°C.

A

13.5 kJ of heat are released.

6g * (1mole/ 18g/mole H2O) = .333
.333 * 40.66 = 13.5

33
Q

What type of intermolecular force causes the dissolution of CaCl2 in water?

A

ion-dipole force

34
Q

Choose the molecule or compound that exhibits dipole-dipole forces as its strongest intermolecular force.

A

SO2

35
Q

How much energy is required to vaporize 98.6 g of ethanol (C2H5OH) at its boiling point, if its ΔHvap is 40.5 kJ/mol?

A

86.7 kJ

36
Q

How much energy is required to heat 36.0 g H2O from a liquid at 65°C to a gas at 115°C? The following physical data may be useful.

ΔHvap = 40.7 kJ/mol

Cliq = 4.18 J/g∘C

Cgas = 2.01 J/g∘C

Csol = 2.09 J/g∘C

Tmelting = 0∘C

Tboiling = 100∘C

A

87.7 kJ

First, you need to heat the sample of water from 65C to the boiling point, 100C:
q = m c (T2-T1) = 36.0 g (4.18 J/gC) (100 - 65 C)
q = 5267 J

Next, you need to vaporize that sample at 100 C:
q = 36.0 g / 18.0 g/mol X 40.7 kJ/mol = 81.4 kJ

Finally, you need to heat the steam from 100C to 115C:
q = m c (T2-T1)
q = 36.0 g (2.01 J/gC)(115-100C) = 1085 J

Now, convert everything to kJ and add them together to get 87.8 kJ. So A is correct.

37
Q

Place the following substances in order of increasing vapor pressure at a given temperature.

        NF3        NH3       BCl3
A

NH3 < NF3 < BCl3

38
Q

What is VSEPR

A

Valence shell electron pair repulsion

VSEPR theory is used to predict the arrangement of electron pairs around non-hydrogen atoms in molecules, especially simple and symmetric molecules, where these key, central atoms participate in bonding to two or more other atoms; the geometry of these key atoms and their non-bonding electron pairs in turn determine the geometry of the larger whole.

39
Q

How much heat is released when 115 g of steam at 100.0°C is cooled to ice at -15.0°C? The enthalpy of vaporization of water is 40.67 kJ/mol, the enthalpy of fusion for water is 6.01 kJ/mol, the molar heat capacity of liquid water is 75.4 J/(mol ⋅ °C), and the molar heat capacity of ice is 36.4 J/(mol ⋅ °C).

Would someone be willing to show me the steps? I’m a little lost to this problem

A

Since all the given constants are in moles, convert the mass of water to moles:
(115 g) / (18.01532 g H2O/mol) = 6.3835 mol H2O

(40. 67 kJ/mol) x (6.3835 mol) = 259.617 kJ from condensing the steam
(75. 4 J/(mol⋅°C)) x (6.3835 mol) x (100 - 0) °C = 48132 J = 48.131 kJ from cooling the water to 0°C
(6. 01 kJ/mol) x (6.3835 mol) = 38.365 kJ from freezing the water
(36. 4 J/(mol⋅°C)) x (6.3835 mol) x (0 - (-15.0)) °C = 3485 J = 3.485 kJ from cooling the ice to -15°C
259. 617 kJ + 48.131 kJ + 38.365 kJ + 3.485 kJ = 350 kJ total

Spring 2018 (13 decks)

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