Bonding, Intermolecular Forces, and Thermodynamics Flashcards
How do you calculate formal charges?
FC = (valence e- in neutral atom) - dots - sticks
Breaking a bond is always an _____ process
endothermic
Metallic bonds are formed between atoms with _____ electronegativity (metals with metals)
low
In metallic bonds, e- are _____ among all the atoms
delocalized
Compounds with metallic bonds are _____ (insulators or conductors) while the compounds with covalent bonds are ______ (insulators or conductors)
1) conductors 2) insulators
What are coordinate covalent bonds?
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
What is bond dissociation energy?
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
What is homolytic bond cleavage?
refers to the type of bond breaking where one e- goes to each fragment of the molecule, creating 2 radicals
What is heterolytic bond cleavage?
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
What is dissociation of a molecule?
refers to heterolytic cleavage of that molecule
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 ______
conductor
Ion-dipole forces are produced between ___ and ____ molecules
ions and polar molecules
dipole-dipole forces are produced between ____ molecules
polar
dipole-induced dipole forces are produces between ____ and _____ molecules
polar and nonpolar molecules
What are London dispersion forces?
induced dipole-induced dipole forces
What are the relative strengths of the different types of intermolecular forces from greatest to lowest strength?
ion-dipole (i.e. Na+ in H2O), H-bond, dipole-dipole, London dispersion forces
Where is enthalpy stored?
stored within chemical bonds are any attractive force
How can you calculate the enthalpy change of a reaction?
total enthalpy required can be estimated by: sum of bonds broken minus sum of bonds formed
What’s the difference between the temperature in standard conditions and standard temperature and pressure?
temp in standard conditions = 298K (25ºC)
in standard temp and pressure (STP), temp = 0ºC
Reaction: 2H2O2 → 2H2O + O2
How many H-O, O-O, and O=O bonds are being broken and formed?
Bonds broken = 4 H-O bonds and 2 O-O bonds
Bonds formed = 4 H-O bonds and 1 O=O bond
How do you calculate enthalpies of formation for an overall reaction?
Σ(n•deltaHºf of products) - Σ(n•deltaHºf of reactants)
n = the stoichiometry coefficent of each reagent/product
Example of calculating deltaH: 2NH3 + CO2 → CO(NH2)2 + H2O
((1 x deltaHºf of CO) + (1 x deltaHºf of H2O)) - ((2x deltaHºf of NH3) + (1 x deltaHºf of CO2))
What is Hess’s Law?
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.
What are 2 important rules to following when applying Hess’s Law?
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
Entropy is the measurement of disorder. In other words, it measures potential ________
randomness
Increasing the number of particles ______ (increases or decreases) entropy
increases
Does changing from a solid to a liquid to a gas increases or decrease entropy?
increases (because you are increasing the potential randomness of the molecules)
2NH3 → N2 + 3H2
Is this equation expressing an increase or decrease in entropy and why?
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.
increasing temperature _____ entropy
increases
True or false: Combustion is spontaneous at all temperatures
True
In Gibbs free energy equation, if delta H is negative and TdeltaS is positive, what will delta G always be?
In these conditions, delta G will always be negative and therefore the rxn is always spontaneous regardless of temperature
Is freezing water (going from liquid to solid) yield a positive or negative deltaS value?
negative (because this is not a spontaneous process)
Do spontaneous processes have a positive or negative deltaS value?
positive value
Do nonspontaneous processes have a positive or negative deltaS value?
negative
When freezing water, what will the value of deltaH be and why?
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.
Freezing water is an exothermic process, therefore deltaH is negative. Is freezing water always a spontaneous process? Explain.
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
Will dephosphorylation of ATP yield a positive or negative value for deltaH? deltaS?
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
Is dephosphorylation of ATP spontaneous?
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)
Which 2 diatomic molecules in their standard state are not found in the gas phase? What phase are they in?
Iodine: I2 is found as a solid in its standard state
Bromine: Br2 is found as a liquid in its standard state
What does sublime mean?
to volatize from liquid to gas
What does anhydrous mean?
means without the presence of water: “an” = without, “hydrous” = water
What is heat of fusion?
the energy needed for one gram of a solid to melt without any change in temperature
What is heat of vaporization?
The energy needed for one gram of a liquid to vaporize (boil) without a change in pressure
Out of N2, Br2, Hg, and Al, which should have the highest enthalpy of vaporization? Explain.
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.
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?
According to Hess’s Law, sublimation of 1 mole of water is 6 + 40.7 = 46.7kJ/mol
What is the heat of formation of any element in its naturally occuring form?
zero i.e. the heat of formation of O2 gas is zero
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 = B
The reason A and D are wrong is because they are talking about kinetics. The question is asking about thermodynamic principles.
Rxns with a positive H and negative S are always ______
spontaneous (because a negative minus a negative will always create a more negative value)
If H is positive and S is negative, the rxn will always be ______
nonspontaneous (because a positive minus a negative is really adding the two values together, which will always produce a positive integer)
isoelectronic species have the same ______
electronic configurations (and hence the same amount of e-)
The dissolution of NaCl is an endothermic process. Why?
because breaking bonds is an endothermic process
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?
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.
The greater the value of Ksp, the more soluble a compound is.
deltaGºdiss= -RTlnKsp
Will the greatest or the smallest value of Ksp give you the smallest deltaG value?
The greater the Ksp value, the smaller the deltaG value will be.
Ksp > 1 will yield a negative delta G value
Ksp < 1 will yield a positive delta G value
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 deltaHºdiss 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 = 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+
Which have shorter bonds, single or double bonds?
double bonds are shorter than single
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
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
How many e- are found in pi bonds in acetylene (C2H2)?
4
