Short answer Flashcards
Chemical nrg is stored in …
bonds
The ability to do work
energy
For any multi-step chemical change, the net enthalpy change = the sum of the changes in enthalpy values of the steps
Hess’s Law
The energy of motion of an object
kinetic energy
positive enthalpy
endothermic
Describe the difference between path function and state function
path function depends on how the change takes place
state function is irrelevant to the path taken from reactants to products
Used to measure heat flows during a chemical reaction
calorimetry
negative enthalpy
exothermic
The nrg required to break one particular chemical bond in a gaseous substance
bond energy
A form of potential nrg according to Einstein
mass
SI unit for energy
joule
the displacement of an object against an opposing force
work
type of energy described by k(q1 x q2)/r
electrical
the amount of energy transferred from a warmer object to a cooler one
heat
If a sample of gas is expanded and cooled, would the delta E be positive or negative?
Negative
Cooling - loses nrg as heat
Expanding - gas is pushing out on atmosphere, gas is doing work on surroundings, loses nrg
State the sequence of equations that lead to acid rain, beginning with NiS(s)
NiS(s) + 3/2 O2(g) –> NiO(s) + SO2(g)
SO2(g) + 1/2 Os(g) –> SO3(g)
SO3(g) + H2O(l) –> H2SO4(aq)
When calculating pressure of a gas at high pressure, why are intermolecular forces important, and how are they taken into account in the VdW’s equation?
At high pressure, gas molecules are closer together and attract each other more. The lower the volume, the less ideal the gas bc intermolecular forces dominate
What two properties of light are brought together by Planck’s equation E=hv?
Wave properties and particle properties
Explain the relationship between atomic radius and electronegativity
Atomic radius decreases as electronegativity increases bc electrons are pulled closer to the nucleus
Why are some electron configurations not as AFBAU predicts them?
Electrons move to fill or half fill sub shells so the atom is more stable
List the six intermolecular forces in order of increasing strength, including their approximate magnitudes
1) ion - dipole 40-600 KJ/mol
2) dipole - dipole 5-25 KJ/mol
3) H bond 10-40 KJ/mol
4) ion - induced dipole 3-15 KJ/mol
5) dipole - induced dipole 2-10 KJ/mol
6) dispersion 0.05-40 KJ/mol
Why is hexane not soluble in water?
EN difference btw C-H is not enough to be polar so there is no attraction to polar water molecules
What is the difference btw LUMO and HOMO molecular orbitals?
Lowest Unoccupied Molecular Orbital - lowest nrg orbital with no electrons
Highest Occupied Molecular Orbital - highest nrg orbital with an electron
What is the difference btw conjugated and unconjugated bonds?
Conjugated - LUMO and HOMO are close in nrg, lower nrg photon required to move an electron from HOMO to LUMO, visible light
Unconjugated - high nrg, UV light
Formal charge
The bond arrangement that allows each atom to be assigned the closest number of electrons as its number of valence electrons # valence e- - # e- assigned to atom in configuration
What are the four properties of liquids?
Surface tension
Capillary
Viscosity
Vapour pressure
What is the strongest type of intermolecular force between HCl and CCl4?
dipole - induced dipole
CCl4 non-polar bc it is symmetrical
HCl polar
What kind of hybrid orbitals are used by central atom S in SF2?
AX2E2
sp3
Why does Fe have two common ions, 2+ and 3+?
Either the two 4s electrons are removed, or the two 4s electrons and one 3d electron are removed (half fulled sub shells are more stable)
Why is BH3 not polar? Why is NH3 polar?
BH3 is symmetrical
NH3 is not symmetrical and so has a net dipole
An electron is removed from a molecule and the bond length decreases. What can be concluded about the MO of the electron that was removed?
bond length decreases => bond strength increases => bond order increases, therefore electron must have been removed from an anti bonding orbital
Explain two reasons why gases do not obey the ideal gas law at high pressures
Molecules occupy volume => increases pressure above predicted
Molecules attract one another => reduces the pressure below predicted
Why does the temperature of the atmosphere go through a max at an altitude of 30km?
Concentration of ozone is at a max at 30km. Ozone absorbs infrared radiation and causes warming
Why does a constant pressure calorimeter not give a direct measurement of the internal energy change of a rxn?
Measurement at constant pressure yields enthalpy change of the system which differs from internal energy change by pV
Why can an electron move from one lobe of an orbital to another without existing in the node?
Electrons can exist as waves, wave can have an amplitude of zero at the node
Name four ways H can be stored for use as fuel in automobiles
Compressed gas
Liquid
Carbon nanotubes
In metal such as Palladium
Write the four reactions of the Chapman cycle that explain the existence of ozone in the stratosphere
O2 + hv –> 2O
O + O2 –> O3
O3 + hv –> O + O2
O + O3 –> 2O2
State Dalton’s law of partial pressures
The total pressure of a gas sample is equal to the sum of the partial pressures of the individual gases present
Explain why delta E is more positive than delta H when there is a net increase in number of moles of a reaction
An increase in n means there is an increase in volume and
E = H + pV so E is more positive than H
Why does Ne light only give photons of a few specific colours?
Photon nrg is equal to the difference between two electron nrg levels, so since e- nrg levels are quantized, photon nrg levels from an atomic light source must also be quantized
Define enantiomers
Enantiomers are two molecules that are non-superimposable mirror images of one another
Why is butanol less soluble in water than ethanol?
Butanol has a longer non-polar chain and is therefore less polar, so it with be less soluble in a polar molecule like water
Graphite is the most stable phase of Carbon. Why does diamond not spontaneously turn into graphite?`
In fact it does, but the process is too slow to observe in our lifetime
Molarity
Molality
wt%
Mole fraction
moles solute / volume solution
moles solute / Kg solvent
mass solute / mass solution
Moles solute / moles solution
Why would the actual pressure (calculated by VdW’s eqn) be lower than the pressure calculated by the ideal gas las?
Higher?
Lower than ideal pressures are caused by the attractive forces btw molecules
Higher pressures are caused by the unaccounted for fact that gas molecules have volume and occupy space
Why does ice float on water?
Strong H bonds hold water molecules in ice in an open, low density structure
Why does solids hexane sink in liquid hexane?
Weak dispersion forces cannot hold molecules in an open structure and so the dense solid sinks in the liquid
Compare the average molecular kinetic nrg of 1 mol of NH3 in 1L at 500 degrees C and 3.35 mol O2 in 25L at 500 degrees C
The average KE are the same because the two samples are at the same temperature
State function and three examples
A function whose value does not depend on the path taken from reactants to products nor on the reaction rate
Enthalpy (H), internal nrg (E), distance between two cities
Pauli exclusion principle
No two electrons in an atom have identical quantum numbers
Name three physical properties of molecules predicted by MO theory not predicted by hybrid orbital theory
Magnetic properties
Bond length
Bond energy
Why is diamond so much harder than graphite?
Diamond - sp3 hybridization results in strong 3D lattice
Graphite - sp2 with p-orbital left over, p overlap leads to weak bonds
Why does CO2 evolve from solution when you leave an open carbonated beverage at room temperature?
Opening the drink exposes the liquid to lower pressure (Henry’s law says lower pressure = lower solubility of the gas)
As the solution warms, gases become less soluble
