Thermochemical Principles Flashcards
How many types of subshells are there?
4
What are the 4 subshells?
s, p, d, f
Each subshell contains orbitals that contain how many electrons?
2
How many orbitals does the S subshell have
1 orbital
How many orbitals does the P subshell have
3 orbitals
How many orbitals does the D subshell have
5 orbitals
What is the order that we fill up the subshells in?
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
so order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 5f
What are the 3 steps to fill electron configurations?
1) Fill up to minimize energy of an atom (Aufbau’s principal) - subshells must fill completely before next level is filled.
2) Each orbital can hold a max of 2 electrons in opposite spin (Pauli’s exclusion principal)
3) Each orbital is filled with 1 electron before any pair (Hunds rule)
What is the electron configuration for Br?
(Hint 35)
Br: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵
What is the electron configuration for V?
(Hint 23)
V: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d³
What is the electron configuration for Ni²⁺?
(Hint 26)
Ni²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸
What is the electron configuration for Sc?
(Hint 21)
Sc: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹
What is the electron configuration for Ga?
(Hint 31)
Ga: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹
What is the electron configuration for Fe³⁺?
(Hint 23)
Fe³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵
What is the electron configuration for S?
(Hint 16)
S: 1s² 2s² 2p⁶ 3s² 3p⁴
What is the electron configuration for Co?
(Hint 27)
Co: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷
What is the electron configuration for Cr³⁺?
(Hint 21)
Cr³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³
What is the 4s² rule for Transition Metals?
- Transition metals lie from Sc to Zn
- They form ions by losing 4s² electrons first
- They then lose a 3d electron if necessary
- 4s electrons are a lower energy level than 3d, so they are EASIER to remove (which is why they are removed first).
E.g
Ti: 1s² 2s² 2p⁶ 3s² 3p⁶ ‘4s²’ 3d² (22e⁻)
Ti⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ ‘ ‘ 3d² (20e⁻)
Atomic radius _____________ as you go across a period
decreases
Who has a bigger radius, Li or F?
Li and F are both in period 2 so they both have 2 electron shells. Li has 3+ protons and 3- electrons. F has 9+ protons and 9- electrons. They have the same amount of ‘shielding’ as both have 1 inner electron shell shielding the attractive force of the nucleus from the valence shell. However, F has a greater nuclear charge, because 9 protons are attracting the valence shell. As a result the valence shell of F is pulled in closer than that of Li. Hence F has a smaller radius.
Atomic radius _____________ as you go down a group
increases
Who has a bigger radius, Al or B?
B and Al are both in group 13. B has 5+ protons, 5- electrons and 2 electron shells. Al has 13+ protons, 13- electrons and 3 electron shells. Although Al has a ‘greater nuclear charge’ than B (so we might expect Al to pull valence in e- more strongly), Al has a larger radius than B. Al has ‘one more electron shell’ than B. This extra shell forces the radius of Al to be bigger because the valence shell is physically further from the nucleus. Further more, the 2 inner shells of Al act to ‘shield’ the valence shell from the pull of the nucleus resulting in a larger radius for Al.
As you go across a period, electronegativity _____________
increases
Electronegativity is the attraction an atom has for bonding e___________
electrons
Explain this data: Electronegativity O=3.5 B=2.0
O has 8+ protons, 8- electrons and has 2 electron shells. B has 5+ protons, 5- electrons and 2 electron shells. O and B both have 2 shells. However O has 3 more protons in its nucleus. This means it has ‘greater electrostatic attraction’ for electrons ‘in a bond’ and thus a greater ‘electronegativity’. Both have 2 shells, so they have the same amount of shielding.
What is electronegativity a measure of?
Electronegativity is a measure of attraction an atom has for electrons in a bond.
It is a number from 0-4 with no unit.
What atom is the most electronegative?
Fluorine
The ____________ an atom’s electronegativity value, the more strongly it _________ bonding electrons to itself.
higher
attracts
As you go _________ a group, electronegativity ______________.
down
decreases
What is ionisation energy?
The energy required to remove one MOLE of ELECTRONS from a MOLE of atoms in the GASEOUS STATE.
What units does ionisation energy have?
kJmol⁻¹
How would you write the equation for the Cl atom for ionisation energy?
Cl₍g₎ → Cl⁺₍g₎ + e⁻
The 1st ______________ energy is the energy required to __________ the 1st valence electron. We can also have 2nd, 3rd, 4th….. ionisation energies for removing successive electrons (with the energy required ______________ each time.
ionisation
remove
increasing
As you go _________ a period, Ionisation energy _____________.
across
increases
As you go ________ a group, ionisation energy _____________.
down
decreases
What are the 5 steps to drawing a Lewis diagram?
1) Count the total number of valence electrons
2) Draw central atom (electron positive) surrounded by outer atoms.
3) Place paired electrons in each bonding position
4) Distribute remaining electrons around OUTER atoms, than central atoms. (Octet rule)
5) Create double/triple bonds where needed (Octet rule).
Draw a Lewis diagram for H₂O using the 5 steps
Step 1:
H 1
H 1
O 6
______
= 8
Step 2:
H O H
Step 3:
H : O : H
Step 4
‥
H : O : H
‥
Draw a lewis diagram for BeH₂
H : Be : H
Draw a lewis diagram for N₂
: N : : : N :
What does INTERmolecular forces mean?
BETWEEN molecules
What does INTRAmolecular forces mean?
WITHIN a molecule/substance. E.g covalent bonds, ionic bonds, metallic bonds
How many types of attractive forces between molecules are there?
3
What attractive force between molecules is the strongest?
Hydrogen bond
What is the middle strongest/weakest attractive force between molecules?
Permanent dipole face
What is the weakest attractive force between molecules?
Temporary dipole face (also known as temporary dipole - dipole/induced dipole-dipole, London forces)
A Temporary Dipole Force is a very _____ bond/force __________ neighbouring molecules.
WEAK
BETWEEN
What is a Temporary Dipole Force caused by?
It is caused by an UNEVEN distribution of ELECTRONS in one end of a molecule.
What does an UNEVEN distribution of ELECTRONS in one end of a molecule cause? (Related to a temporary dipole force)
It causes electrons in the neighbouring molecule to be repelled, which creates a weak, TEMPORARY force of attraction between the 2 molecules. This continues like a wave from molecule to molecule… But as soon as it is formed it disappears again.
A Permanent Dipole Force is a ___________ type of intermolecular bond between neighbouring molecules (but is still ‘weak’).
STRONGER
What is a Permanent Dipole Force caused by?
It is caused by POLAR molecules with PERMANENT +/- DIPOLES being attracted to one another. Because the dipoles on a polar molecule never go away, this attraction is always maintained, hence the name ‘PERMANENT’
What is a Hydrogen Bond in relation to P.D.F’s?
A hydrogen bond is a special, strong type of Permanent Dipole Force (P.D.F).
Is the Hydrogen bond the strongest of intermolecular forces?
Yes
When can a Hydrogen bond occur?
Only in specific molecules: the molecule must have an H-F, H-O or H-N bond within it. E.g H₂O, NH₃, HF.
Which 3 elements are especially ELECTRONEGATIVE and thus form especially STRONG DIPOLES?
F, O, N
In a Hydrogen Bond neighbouring molecules are ________ attracted to each other at opposite dipoles. These molecules have a _________ BOILING POINT as it takes a lot of heat energy to break the hydrogen bond.
STRONGLY
HIGH
What does the abbreviation VSEPRT stand for in relation to identifying shapes from lewis diagrams?
Valence
Shell
Electron
Pair
Repulsion
Theory
What does the VSEPRT theory mean?
That electrons are negatively charged, so will REPEL and position themselves as FAR APART as possible around the central atom.
What are the 12 shapes of molecules?
1) Linear
2) Bent (3 regions)
3) Bent (4 regions)
4) Trigonal Planar
5) Trigonal Pyramidal
6) T-shaped
7) Tetrahedral
8) See-saw
9) Square Planar
10) Trigonal Bipyramidal
11) Square Pyramid
12) Octahedral
What does this indicate a bond is doing?
◄
The bond is ‘out of the page’
What does this indicate a bond is doing?
⋯
The bond is ‘into the page’
What is a linear shape and what is the bond angle?
Two regions of negative charge on central atom and no lone pairs.
Bond angle 180°
What is a Bent (3 regions) shape and what is the bond angle?
Three regions of negative charge - two bonding and one lone pair.
Bond angle 120°
What is a Bent (4 regions) shape and what is the bond angle?
Four regions of negative charge - two bonding and two lone pairs.
Bond angle 109°
What is a Trigonal Planar shape and what is the bond angle?
Three regions of negative charge on the central atom, all bonding and no lone pairs.
Bond angle 120°
What is a Trigonal Pyramidal shape and what is the bond angle?
Four regions of negative charge on the central atom, three bonding and one lone pair.
Bond angle 109°
What is a T-shaped shape and what is the bond angle?
Five regions of negative charge on the central atom, three bonding and two lone pairs.
Bond angle 90°
What is a linear shape and what is the bond angle?
What is a Tetrahedral shape and what is the bond angle?
Four regions of negative charge on the central atom, all are bonding with no lone pairs.
What is a See-saw shape and what is the bond angle?
Five regions of negative charge on the central atom, four bonding and one lone pair.
Bond angle 90° and 120°
What is a Square planar shape and what is the bond angle?
Six regions of negative charge on the central atom, four bonding and two lone pairs.
Bond angle 90°
What is a Trigonal Bipyramidal shape and what is the bond angle?
Five regions of negative charge around the central atom, five bonding and no lone pairs.
Bond angle 90° and 120°
What is a Square pyramid shape and what is the bond angle?
Six regions of negative charge around the central atom, five bonding and one lone pair.
Bond angle 90°
What is a Octahedral shape and what is the bond angle?
Six regions of negative charge around the central atom, six bonding and no lone pairs.
Bond angle 90°
What is a linear shape and what is the bond angle?
When does a polar bond occur?
When there is a difference in electronegativity
All matter contains __________ ENERGY & _____________ ENERGY. We call this combined energy ‘ENTHALPY’.
KINETIC
POTENTIAL
What is the symbol for Enthalpy?
H
What is the symbol for a ‘Change in Enthalpy’ in a reaction?
△H
What is the units for Enthalpy?
kJmol⁻¹
What is an EXOthermic reaction?
A reaction which transfers heat energy from the system TO the surroundings so the surroundings feel warmer to the touch.
What is an ENDOthermic reaction?
A reaction which takes heat energy FROM the surroundings into the system, so the surroundings feel cooler to the touch.
What is the symbol for the Standard Heat of Fusion?
△fusH°
What is the Standard Heat of Fusion?
The enthalpy change when 1 MOLE of substance is MELTED at its MELTING POINT.
H₂O₍ₛ₎ → H₂O₍ı₎
△fusH°= 6.0kJmol⁻¹
What is the symbol for the Standard Heat of Vaporisation?
△vapH°
What is the Standard Heat of Vaporisation?
The enthalpy change when 1 MOLE of substance is VAPORISED at its BOILING POINT.
H₂O₍ı₎ → H₂O₍g₎
△vapH°= 47.0kJmol⁻¹
What are the 5 different types of enthalpy?
1) △fusH°
2) △vapH°
3) △subH°
4) △fH°
5)△cH°
What is the symbol for the Standard Heat of Sublimation?
△subH°
What is the Standard Heat of Sublimation?
The enthalpy change when 1 MOLE of substance SUBLIMES at its sublimation point.
CO₂₍ₛ₎ → CO₂O₍g₎
△subH°= ~47.0kJmol⁻¹
What does the Heating Curve of Water show?
How the temperature of water changes as it is heated over time.
What is the Heating Curve of Water?
A series of climbs and vertical sections, representing changes in kinetic energy or potential energy of the water.
What does the Heating Curve of Water involve?
△fusH° and △vapH°
What does a slope on a graph of a heating curve represent?
Increasing temperature
When there is a slope on a heating curve graph that represents increasing temperature what does this mean?
When temperature increases, the kinetic energy of the water particles is increasing. This energy causes the particles to VIBRATE more quickly. NO state change occurs so SOLID STAYS SOLID and LIQUID STAYS LIQUID.
What does a flat line on a heating curve graph represent?
A change in state
When there is a flat line on a heating curve graph that represents a change in state what does this mean?
The water particles change state: solids turn to liquid, liquid turns to gas. There is NO temperature change at this point. Heat energy is used to BREAK the INTERMOLECULAR FORCES (IMF) between water molecules, and the potential energy of molecules increase. When solid changes to liquid SOME IMF BREAK, when liquid changes to gas, THE REMAINING IMF BREAK.
What is the symbol for the Standard Heat of Formation?
△fH°
What is the Standard Heat of Formation?
The enthalpy change when 1 MOLE of a substance is FORMED under standard conditions from its pure elements.
½N₂₍g₎ + 1½H₂₍g₎→ NH₃₍g₎
△fH°= -46.1kgmol⁻¹
All ____________ (e.g O₂, Cl₂, Fe, Mg) have a △fH° value of ___ because we can not write a △fH° equation for a single element.
ELEMENTS
0
What is the Formation equation for H₂O?
H₂₍g₎ + ½O₂₍g₎ → H₂O₍ı₎
△fH°= -241kJmol⁻¹
What is the Formation equation for NaCl?
Na₍ₛ₎ + ½Cl₂₍g₎ → NaCl₍ₛ₎
△fH°= -411kJmol⁻¹
What is the Formation equation for NCl₃?
½N₂₍g₎ + 1½Cl₂₍g₎ → NCl₃₍ₛ₎
△fH°= +230kJmol⁻¹
What is the symbol Standard Heat of Combustion?
△cH°
What is the Standard Heat of Combustion?
The enthalpy change when 1 MOLE of substance is COMBUSTED (burnt) in OXYGEN with all reactants & products in STANDARD STATES.
For the Standard Heat of Combustion, if the reactant has C and H in it, the products of combustion will be CO₂ & H₂O what would the equation be?
C₂H₆₍g₎ +3½O₂₍g₎ → 2CO₂₍g₎ + 3H₂O₍ı₎
△cH° = -1499kJmol⁻¹
For the Standard Heat of Combustion, if reactant contains no H, the product of combustion will be CO₂ (or if sulfur is being burnt it will be SO₂), what would the equation be?
C₍ₛ₎ + O₂₍g₎ → CO₂₍g₎
△cH° = -393kJmol⁻¹
S₍ₛ₎ + O₂₍g₎ → SO₂₍g₎
△cH° = -400kJmol⁻¹
For the Standard Heat of Combustion, if the reactant contains NO C, the production of combustion will be H₂O, what would the equation be?
H₂₍g₎ + ½O₂₍g₎ → H₂O₍ı₎
△cH° = -285kJmol⁻¹
At 25°C what will the following molecules form?
Cl₂
N₂
Na
H₂
O₂
Cl₂ = gas
N₂ = gas
Na = solid
H₂ = gas
O₂ = gas
What is Hess’s law?
If a reaction can be represented as a COMBINATION of other reactions, then the △H of the reaction is also as COMBINATION of the △H’s of the other reactions.
What may a Hess’s law problem format look like?
&
What are Equation 1, Equation 2 and Equation 3 in Hess’s law?
“Equation A” The equation you want to find △H for.
1, 2 and 3 are the feeder equations you will MANIPULATE (i.e multiply, divide, reverse) to calculate △rH for “Equation A”.
What are the 5 tips for Hess’s law?
1) Keep the STATE SYMBOL in equations.
2) If you need to REVERSE an equation, REVERSE the △H value too.
3) If you need to MULTIPLY an equation then MULTIPLY the △H value too.
4) Circle species you want to keep.
5) Cross out species you need to cancel (you can only cancel species that are on OPPOSITE sides of the arrow).
What are the 5 steps to using Hess’s law?
1) manipulate given equations to most closely resemble the equation of interest (perform same operation on △H as on the equations).
2) Add new reactions together.
3) Cancel out any compounds that are the same on opposite sides of a reaction arrow.
4) Write new equation and double check it matches the equation of interest.
5) Add H values together to get △H for the equation of interest.
Flip & Scale technique example: Calculate △rH
CO₍g₎ + ½O₂₍g₎ → CO₂₍g₎
- CO₂₍g₎ → C₍ₛ₎ _ O₂₍g₎
△H = 393kJmol⁻¹ - C₍ₛ₎ + ½O₂₍g₎ →CO₍g₎
△H = -111kJmol⁻¹
Flip & Scale:
Flipped: C₍ₛ₎ (✕’d out) + ½O₂₍g₎ → CO₂₍g₎
△H = -393kJmol⁻¹ (Reversed △)
Flipped: CO₍g₎ → C₍ₛ₎ (✕’d out) + ½O₂₍g₎ (✕’d out ½)
△H = +111kJmol⁻¹ (Reversed △)
△rH = -282kJmol⁻¹
1 carbon on the left & 1 on the right.
1 oxygen on the left & 1 on the right.
Answer: CO₍g₎ + ½O₂₍g₎ → CO₂₍g₎
△H = -282kJmol⁻¹
What are the 4 different ways of calculating △H° values?
1) Using heats of formation (△fH°).
2) Using Hess’s law.
3) Using experimental data
4) Change in Bond Energies.
How do you calculate △H using Heats of Formation?
If you are provided with a list of HEATS OF FORMATION values you can use the equation below to calculate △H. This equation is PROVIDED FOR US in the exam. Σ means ‘sum of’ so add the values together.
Equation:
△rH° = Σ△fH° (products) - Σ△fH° (reactants)
Example of what calculating △H using the Heats of Formation looks like:
CH₄₍g₎ + 2C₂₍g₎ →CO₂₍g₎ + 2H₂O₍g₎ △H=?
△fH° CH₄₍g₎ = -75kJmol⁻¹
△fH° H₂O₍g₎ = -285kJmol⁻¹
△fH° CO₂₍g₎ = -393kJmol⁻¹
△rH° = Σ△fH° (products) - Σ△fH° (reactants)
△rH° = Σ△fH°(CO₂ + 2 x H₂O) - Σ△fH°(CH₄ + 2 x O₂)
△rH° = Σ△fH°(-393 + 2 x -285) - (-75 + 2 x 0)
△rH° = -888kJmol⁻¹
If a question provides you with EXPIREMENTAL DATA in a calculating △H° what do you need to do?
Calculate using experimental data with this equation:
q=mc△T
What they mean:
q: Heat energy (J)
m: Mass of WATER (g) of mixture
c: Specific heat of capacity of WATER (4.18J°C⁻¹g⁻¹
△T: Change in temperature (C°0
What is Entropy?
ENTROPY (symbol s) is a measurement of the DISORDER of particles in a system. An increase in entropy occurs when particles become more DISORDED DURING A REACTION.
What rules do you need to follow when describing entropy?
- LOW entropy: Solid particles are ORDERED.
- HIGH entropy: Gas particles are DISORDED
Molecules:
* Low entropy: Have FEWER moles of gas.
*High entropy: Have MORE moles of gas.
State:
* Low entropy: Solid
- High entropy: Ions
Temperature:
* Low entropy: Cold particles (vibrate SLOWLY)
- High entropy: Warmer particle (vibrate FASTER).
The __________ particles move, the more likely they are to be _______________. Therefore, hotter particles have higher entropy.
FASTER
DISORDERED
What is a ‘spontaneous reaction’?
A reaction that occurs in a given set of conditions, without intervention.
What is the rule regarding Entropy and spontaneous reactions?
If ENTROPY of reaction increases… the reaction WILL BE spontaneous.
IN GENERAL: Spontaneous reactions are accompanied by an ____________ in ENTROPY. And are ________________ (release heat).
INCREASE
EXOTHERMIC
What needs to occur in order for an ENDOthermic reaction to be spontaneous?
There needs to have been an INCREASE IN ENTROPY in the REACTION (SYSTEM) which Is GREATER than the DEVCREASE IN ENTROPY of the surroundings.
