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CHEM 1001 > Short answer > Flashcards

Short answer Flashcards

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1
Q

Chemical nrg is stored in …

A

bonds

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2
Q

The ability to do work

A

energy

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3
Q

For any multi-step chemical change, the net enthalpy change = the sum of the changes in enthalpy values of the steps

A

Hess’s Law

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4
Q

The energy of motion of an object

A

kinetic energy

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5
Q

positive enthalpy

A

endothermic

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6
Q

Describe the difference between path function and state function

A

path function depends on how the change takes place

state function is irrelevant to the path taken from reactants to products

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7
Q

Used to measure heat flows during a chemical reaction

A

calorimetry

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8
Q

negative enthalpy

A

exothermic

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9
Q

The nrg required to break one particular chemical bond in a gaseous substance

A

bond energy

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10
Q

A form of potential nrg according to Einstein

A

mass

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11
Q

SI unit for energy

A

joule

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12
Q

the displacement of an object against an opposing force

A

work

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13
Q

type of energy described by k(q1 x q2)/r

A

electrical

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14
Q

the amount of energy transferred from a warmer object to a cooler one

A

heat

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15
Q

If a sample of gas is expanded and cooled, would the delta E be positive or negative?

A

Negative
Cooling - loses nrg as heat
Expanding - gas is pushing out on atmosphere, gas is doing work on surroundings, loses nrg

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16
Q

State the sequence of equations that lead to acid rain, beginning with NiS(s)

A

NiS(s) + 3/2 O2(g) –> NiO(s) + SO2(g)
SO2(g) + 1/2 Os(g) –> SO3(g)
SO3(g) + H2O(l) –> H2SO4(aq)

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17
Q

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?

A

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

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18
Q

What two properties of light are brought together by Planck’s equation E=hv?

A

Wave properties and particle properties

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19
Q

Explain the relationship between atomic radius and electronegativity

A

Atomic radius decreases as electronegativity increases bc electrons are pulled closer to the nucleus

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20
Q

Why are some electron configurations not as AFBAU predicts them?

A

Electrons move to fill or half fill sub shells so the atom is more stable

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21
Q

List the six intermolecular forces in order of increasing strength, including their approximate magnitudes

A

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

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22
Q

Why is hexane not soluble in water?

A

EN difference btw C-H is not enough to be polar so there is no attraction to polar water molecules

23
Q

What is the difference btw LUMO and HOMO molecular orbitals?

A

Lowest Unoccupied Molecular Orbital - lowest nrg orbital with no electrons
Highest Occupied Molecular Orbital - highest nrg orbital with an electron

24
Q

What is the difference btw conjugated and unconjugated bonds?

A

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

25
Q

Formal charge

A 
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
26
Q

What are the four properties of liquids?

A

Surface tension
Capillary
Viscosity
Vapour pressure

27
Q

What is the strongest type of intermolecular force between HCl and CCl4?

A

dipole - induced dipole
CCl4 non-polar bc it is symmetrical
HCl polar

28
Q

What kind of hybrid orbitals are used by central atom S in SF2?

A

AX2E2

sp3

29
Q

Why does Fe have two common ions, 2+ and 3+?

A

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)

30
Q

Why is BH3 not polar? Why is NH3 polar?

A

BH3 is symmetrical

NH3 is not symmetrical and so has a net dipole

31
Q

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?

A

bond length decreases => bond strength increases => bond order increases, therefore electron must have been removed from an anti bonding orbital

32
Q

Explain two reasons why gases do not obey the ideal gas law at high pressures

A

Molecules occupy volume => increases pressure above predicted
Molecules attract one another => reduces the pressure below predicted

33
Q

Why does the temperature of the atmosphere go through a max at an altitude of 30km?

A

Concentration of ozone is at a max at 30km. Ozone absorbs infrared radiation and causes warming

34
Q

Why does a constant pressure calorimeter not give a direct measurement of the internal energy change of a rxn?

A

Measurement at constant pressure yields enthalpy change of the system which differs from internal energy change by pV

35
Q

Why can an electron move from one lobe of an orbital to another without existing in the node?

A

Electrons can exist as waves, wave can have an amplitude of zero at the node

36
Q

Name four ways H can be stored for use as fuel in automobiles

A

Compressed gas
Liquid
Carbon nanotubes
In metal such as Palladium

37
Q

Write the four reactions of the Chapman cycle that explain the existence of ozone in the stratosphere

A

O2 + hv –> 2O
O + O2 –> O3
O3 + hv –> O + O2
O + O3 –> 2O2

38
Q

State Dalton’s law of partial pressures

A

The total pressure of a gas sample is equal to the sum of the partial pressures of the individual gases present

39
Q

Explain why delta E is more positive than delta H when there is a net increase in number of moles of a reaction

A

An increase in n means there is an increase in volume and

E = H + pV so E is more positive than H

40
Q

Why does Ne light only give photons of a few specific colours?

A

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

41
Q

Define enantiomers

A

Enantiomers are two molecules that are non-superimposable mirror images of one another

42
Q

Why is butanol less soluble in water than ethanol?

A

Butanol has a longer non-polar chain and is therefore less polar, so it with be less soluble in a polar molecule like water

43
Q

Graphite is the most stable phase of Carbon. Why does diamond not spontaneously turn into graphite?`

A

In fact it does, but the process is too slow to observe in our lifetime

44
Q

Molarity
Molality
wt%
Mole fraction

A

moles solute / volume solution
moles solute / Kg solvent
mass solute / mass solution
Moles solute / moles solution

45
Q

Why would the actual pressure (calculated by VdW’s eqn) be lower than the pressure calculated by the ideal gas las?
Higher?

A

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

46
Q

Why does ice float on water?

A

Strong H bonds hold water molecules in ice in an open, low density structure

47
Q

Why does solids hexane sink in liquid hexane?

A

Weak dispersion forces cannot hold molecules in an open structure and so the dense solid sinks in the liquid

48
Q

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

A

The average KE are the same because the two samples are at the same temperature

49
Q

State function and three examples

A

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

50
Q

Pauli exclusion principle

A

No two electrons in an atom have identical quantum numbers

51
Q

Name three physical properties of molecules predicted by MO theory not predicted by hybrid orbital theory

A

Magnetic properties
Bond length
Bond energy

52
Q

Why is diamond so much harder than graphite?

A

Diamond - sp3 hybridization results in strong 3D lattice

Graphite - sp2 with p-orbital left over, p overlap leads to weak bonds

53
Q

Why does CO2 evolve from solution when you leave an open carbonated beverage at room temperature?

A

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

CHEM 1001 (2 decks)

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