Bonding, Intermolecular Forces, and Thermodynamics

Question 1

How do you calculate formal charges?

Answer 1

FC = (valence e- in neutral atom) - dots - sticks

Question 2

Breaking a bond is always an _____ process

Answer 2

endothermic

Question 3

Metallic bonds are formed between atoms with _____ electronegativity (metals with metals)

Answer 3

low

Question 4

In metallic bonds, e- are _____ among all the atoms

Answer 4

delocalized

Question 5

Compounds with metallic bonds are _____ (insulators or conductors) while the compounds with covalent bonds are ______ (insulators or conductors)

Answer 5

1) conductors 2) insulators

Question 6

What are coordinate covalent bonds?

Answer 6

Refers to when one atom will donate both of the shared e- in a bond Coordinate covalent bonds are formed between atoms with lone pairs and e- deficient species i.e. the lone e- pair on N from NH3 is donated to the B in BF3 because B is considered e- deficient

Question 7

What is bond dissociation energy?

Answer 7

the energy required to break a bond homolytically (one e- of the bond being broken goes to each fragment of the molecule). This process creates 2 radicals

Question 8

What is homolytic bond cleavage?

Answer 8

refers to the type of bond breaking where one e- goes to each fragment of the molecule, creating 2 radicals

Question 9

What is heterolytic bond cleavage?

Answer 9

aka dissociation: refers to the type of bond breaking where both e- of the e- pair that make up the bond go to one fragment of the molecule, creating an anion and a cation

Question 10

What is dissociation of a molecule?

Answer 10

refers to heterolytic cleavage of that molecule

Question 11

Compounds with ionic bonds are insulators and are brittle, but when ions dissociate in aqueous solution as an electrolyte, the aqueous solution can function as a ______

Answer 11

conductor

Question 12

Ion-dipole forces are produced between ___ and ____ molecules

Answer 12

ions and polar molecules

Question 13

dipole-dipole forces are produced between ____ molecules

Answer 13

polar

Question 14

dipole-induced dipole forces are produces between ____ and _____ molecules

Answer 14

polar and nonpolar molecules

Question 15

What are London dispersion forces?

Answer 15

induced dipole-induced dipole forces

Question 16

What are the relative strengths of the different types of intermolecular forces from greatest to lowest strength?

Answer 16

ion-dipole (i.e. Na+ in H2O), H-bond, dipole-dipole, London dispersion forces

Question 17

Where is enthalpy stored?

Answer 17

stored within chemical bonds are any attractive force

Question 18

How can you calculate the enthalpy change of a reaction?

Answer 18

total enthalpy required can be estimated by: sum of bonds broken minus sum of bonds formed

Question 19

What’s the difference between the temperature in standard conditions and standard temperature and pressure?

Answer 19

temp in standard conditions = 298K (25ºC)

in standard temp and pressure (STP), temp = 0ºC

Question 20

Reaction: 2H₂O₂ → 2H₂O + O₂

How many H-O, O-O, and O=O bonds are being broken and formed?

Answer 20

Bonds broken = 4 H-O bonds and 2 O-O bonds

Bonds formed = 4 H-O bonds and 1 O=O bond

Question 21

How do you calculate enthalpies of formation for an overall reaction?

Answer 21

Σ(n•deltaHº_f of products) - Σ(n•deltaHº_f of reactants)

n = the stoichiometry coefficent of each reagent/product

Example of calculating deltaH: 2NH₃ + CO₂ → CO(NH₂)₂ + H₂O

((1 x deltaHº_f of CO) + (1 x deltaHº_f of H₂O)) - ((2x deltaHº_f of NH₃) + (1 x deltaHº_f of CO₂))

Question 22

What is Hess’s Law?

Answer 22

Hess’s Law states that if a rxn occurs in several steps, then the sum of the energies absorbed or given off in all the steps will be the same as that for the overall rxn.

Question 23

What are 2 important rules to following when applying Hess’s Law?

Answer 23

1) if a rxn is reversed, the sign of deltaH is reversed too
2) if an equation is multiplied by a coefficient, the deltaH must be multiplied by the same value

Question 24

Entropy is the measurement of disorder. In other words, it measures potential ________

Answer 24

randomness

Question 25

Increasing the number of particles ______ (increases or decreases) entropy

Answer 25

increases

Question 26

Does changing from a solid to a liquid to a gas increases or decrease entropy?

Answer 26

increases (because you are increasing the potential randomness of the molecules)

Question 27

2NH₃ → N₂ + 3H₂

Is this equation expressing an increase or decrease in entropy and why?

Answer 27

increase in entropy because you are starting with 2 moles of reagent and ending up with 2 moles of product, which is essentially increasing the number of particles.

Question 28

increasing temperature _____ entropy

Answer 28

increases

Question 29

True or false: Combustion is spontaneous at all temperatures

Answer 29

True

Question 30

In Gibbs free energy equation, if delta H is negative and TdeltaS is positive, what will delta G always be?

Answer 30

In these conditions, delta G will always be negative and therefore the rxn is always spontaneous regardless of temperature

Question 31

Is freezing water (going from liquid to solid) yield a positive or negative deltaS value?

Answer 31

negative (because this is not a spontaneous process)

Question 32

Do spontaneous processes have a positive or negative deltaS value?

Answer 32

positive value

Question 33

Do nonspontaneous processes have a positive or negative deltaS value?

Answer 33

negative

Question 34

When freezing water, what will the value of deltaH be and why?

Answer 34

When you freeze water, the value of deltaH will be negative, which means this is an exothermic process. Freezing water is an exothermic process because when water is froze, it is creating hydrogren bonds, and creating bonds is ALWAYS an exothermic process.

Question 35

Freezing water is an exothermic process, therefore deltaH is negative. Is freezing water always a spontaneous process? Explain.

Answer 35

Freezing is spontaneous at low temperatures, but is nonspontaneous at high temperatures. Ultimately, the spontaneity This is because deltaS is a negative number, which means it is added to the delta H value instead of subtracted. If temperature is great enough, it will make the S value large enough to where delta G becomes a positive number, and therefore the rxn becomes nonspontaneous

deltaG = deltaH - TdeltaS

Question 36

Will dephosphorylation of ATP yield a positive or negative value for deltaH? deltaS?

Answer 36

dephosphorylation of ATP involves breaking bonds, and breaking bonds is always an exothermic process; therefore deltaH will have a positive value

dephosphorylation increases entropy because you are increasing particles: ATP becomes ADP and P

Question 37

Is dephosphorylation of ATP spontaneous?

Answer 37

deltaH and deltaS are both positive, which means that dephosphorylation of ATP is spontaneous at high temps, but nonspontaneous at low temps

(Note this is the opposite of water freezing)

Question 38

Which 2 diatomic molecules in their standard state are not found in the gas phase? What phase are they in?

Answer 38

Iodine: I₂ is found as a solid in its standard state

Bromine: Br₂ is found as a liquid in its standard state

Question 39

What does sublime mean?

Answer 39

to volatize from liquid to gas

Question 40

What does anhydrous mean?

Answer 40

means without the presence of water: “an” = without, “hydrous” = water

Question 41

What is heat of fusion?

Answer 41

the energy needed for one gram of a solid to melt without any change in temperature

Question 42

What is heat of vaporization?

Answer 42

The energy needed for one gram of a liquid to vaporize (boil) without a change in pressure

Question 43

Out of N₂, Br₂, Hg, and Al, which should have the highest enthalpy of vaporization? Explain.

Answer 43

Enthalpy of vaporization is the energy required to convert 1 mole of something from liquid phase to gas phase. Therefore, Al should have the highest enthalpy of vaporization because it is the only molecule listed that is in solid form at standard conditions. Br₂ and Hg are in liquid form at standard conditions, while N₂ is a gas at standard conditions.

Question 44

If the heat of fusion of water is 6kJ/mol and the heat of vaporization of water is 40.7kJ/mol, how much energy is required for to sublime 1 mole of water?

Answer 44

According to Hess’s Law, sublimation of 1 mole of water is 6 + 40.7 = 46.7kJ/mol

Question 45

What is the heat of formation of any element in its naturally occuring form?

Answer 45

zero i.e. the heat of formation of O₂ gas is zero

Question 46

The citric acid cycle consists of rxns that break down acetate into CO₂. Given that some steps are thermodynamically unfavorable, why does the cycle proceed in the forward direction overall?

A) the rate constant for the unfavorable rxn is very large

B) the cycle contains exergonic rxns that drive the energonic rxns forward

C) the activation energies of the unfavorable rxns are lowered by catalysts

Answer 46

Answer = B

The reason A and D are wrong is because they are talking about kinetics. The question is asking about thermodynamic principles.

Question 47

Rxns with a positive H and negative S are always ______

Answer 47

spontaneous (because a negative minus a negative will always create a more negative value)

Question 48

If H is positive and S is negative, the rxn will always be ______

Answer 48

nonspontaneous (because a positive minus a negative is really adding the two values together, which will always produce a positive integer)

Question 49

isoelectronic species have the same ______

Answer 49

electronic configurations (and hence the same amount of e-)

Question 50

The dissolution of NaCl is an endothermic process. Why?

Answer 50

because breaking bonds is an endothermic process

Question 51

The dissoultion of NaCl is an endothermic process and therefore has a positive delta H value. Why does the dissolution of salt occur in waterat room temperature?

Answer 51

because the entropy value of salt dissoultion is positive, and at room temperature this value outweighs the positive deltaH value, thus giving a negative delta G value.

Question 52

The greater the value of K_sp, the more soluble a compound is.

deltaGº_diss= -RTlnK_sp

Will the greatest or the smallest value of K_sp give you the smallest deltaG value?

Answer 52

The greater the K_sp value, the smaller the deltaG value will be.

K_sp > 1 will yield a negative delta G value

K_sp ​< 1 will yield a positive delta G value

Question 53

The deltaH dissociation value for LiCl is negative, while the deltaH dissociation value for NaCl is positive. Which of the following is consistent with the differences in deltaHº_diss for LiCl and NaCl?

A) the electrostatic forces in solid LiCl are much stronger than in solid NaCl, while coordination of water is equivalent for both salts

B) the electrostatic forces in the two solids are appprox equivalent, while water molecules coordinate much more effectively to Na+ than Li+

C) The electrostatic forces in solid LiCl are weaker than in solid NaCl, while water cannot effectively coordinate to the very small Li+ cation

D) the electrostatic forces in solid NaCl are slightly weaker than in solid LiCl, while water far more efficiently coordinates Li+ than Na+

Answer 53

Answer = D

Effective dissolution involves the endothermic step of overcoming the electrostatic charges holding the salts together and the exothermic step of coordinating solvents to the separated ions. Choice A and B would lead to a more negative deltaH for NaCl. Choice C is incorrect because a large negative value of deltaH would be difficult to achieve if water were unable to coordinate Li+. Choice D inc a viable combination of slightly weaker attractive forces in NaCl but much better solvation for Li+

Question 54

Which have shorter bonds, single or double bonds?

Answer 54

double bonds are shorter than single

Question 55

How many of which type of orbitals are used to create the hybrid orbitals on carbon in a molecule of ethylene (C2H4)?

A) 1 s and 1 p

B) 2 s and 2 p

C) 1 s and 3 p

D) 1 s and 2 p

Answer 55

D) 1 s and 2 p orbitals

the C are sp2 hybridized and therefore have 1 s atomic orbital and 2 p atomic orbitals that form the hybrid orbitals

Question 56

How many e- are found in pi bonds in acetylene (C2H2)?

Answer 56

4