Shapes and Trends
This molecule shape has 5 regions of electron density, 3 bonded and 2 non-bonded (lone pairs)
T-Shaped
All molecules have these forces.
Temporary dipoles.
This law states that the total enthalpy change for a reaction is the same regardless of the number of steps it takes.
What is Hess's Law?
What are the two key ideas for the system entropy changes?
Number of moles in the reaction and the state changes.
How many cats does Whaea Jamie have?
3
What are the two key ideas for determining molecule polarity
- Bond dipoles (δ - and δ +)
- Symmetry of bond dipoles (do they cancel each other out)
Hydrogen bonded to either nitrogen, oxygen or fluorine, resutling in a very large bond dipole, creating a strong intermolecular force bewteen molecules.
If a reaction has a positive (ΔH = +) value, it is described as this.
What is endothermic?
In an exothermic reaction, what is the reason for a change in entropy of the surroundings?
Heat energy is displaced into the surroundings, resulting in surrounding particles gaining kinetic energy (moving faster), resutling in more disorder in the surroundings, so entropy increases.
Who is this years Bird of the Year?
Karure, the Chatham Islands black robin
Draw the lewis diagram for the following molecule and identify its shape:
ICl4-
Lewis diagram has I with 4 bonds and 2 lone pairs, do not forget the square brackets and negative charge!
Electron geometry = Octahedral
Molecule geometry = Square planar
Identify the intermolecular forces for the following molecule: CH3CH2OH (ethanol)
Temporary dipoles
Permanent dipoles
Write the reaction for ΔsubH (NH4Cl(s)) = 176 kJ/mol
NH4Cl(s) -> NH4Cl(g) ΔsubH = 176kJ/mol
For a reaction to be spontaneous, what must happen?
The overall entropy change must be positive, ΔS(total) = positive
Nominate someone from your group to come up to the front.
Draw a perfect circle:
https://neal.fun/perfect-circle/
XeF4 (xenon tetrafluoride) is a square planar molecule, it contains 4 bonds and 2 lone pairs. Identify the polarity of this molecule and explain why.
XeF4 is non-polar, due to the Xe-F bonds being spaced equally with the lonw pairs at the top and bottom of the Xe atom. This results in all dipoles cancelling each other out and resulting in a non-polar molecule.
If Mr Brown has seen it and thiks it is good, you get the points.
Using the formula: ΔrH = ∑n(products) - ∑n(reactants)
Calculate the enthalpt change for the following reaction:
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)
∆fH° (C2H5OH(l)) = –277 kJ/mol
∆fH° (CO2(g)) = −394 kJ/mol
∆fH° (H2O(l)) = −286 kJ/mol
ΔrH = ∑n(products) - ∑n(reactants)
= [(2 x -394) + (3 x -286)] - [-277]
= -1646 + 277
= -1370 kJ/mol (3 s.f.)
Identify the system entropy change for the following reaction:
Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)
Number of moles changes from 3 -> 2, which is becoming more organised, so negative entropy change.
A state change of solid to gas occurs, which is an increase in disorder, so positive entropy change.
Overall for the system is (possibly) netural change.
What are the two key ideas to explain for all periodic trends (radii, ionisation energy and electronegativity)?
- Number of energy levels (more electron shielding or repulsion)
- Number of protons (more means stronger nuclear charge and attractive force)
Explain the reason why non-polar molecules can have different boiling points?
As the molecule becomes larger, it has a larger electron cloud, resulting in stronger temporary dipoles forming, increasing the strength of the intermolecular forces and a higher boiling point.
The equation for the formation of Al2Cl6(s) is:
2Al(s) + 3Cl2(g) → Al2Cl6(s)
Calculate the enthalpy change, ∆rH°, for this reaction using the following data (Hess's Law):
2Al(s) + 6HCl(aq) → Al2Cl6(aq) + 3H2(g) ∆rH° = –1003 kJ/mol
H2(g) + Cl2(g) → 2HCl(g) ∆rH° = –184 kJ/mol
HCl(g) → HCl(aq) ∆rH° = –72.4 kJ/mol
Al2Cl6(s) → Al2Cl6(aq) ∆rH° = –643 kJ/mol
2Al(s) + 6HCl(aq) → Al2Cl6(aq) + 3H2(g) – 1003
3H2(g) + 3Cl2(g) → 6HCl(g) – 552
6HCl(g) → 6HCl(aq) – 434.4
Al2Cl6(aq) → Al2Cl6(s) + 643
2Al(s) + 3Cl2(g) → Al2Cl6(s) –1346.4 kJ/mol
∆rH° = –1350kJ/mol (3s.f.)
Wild spot (selecting group only) - Chose positive or negative
Postive - Give another group 500 points
Negative - Take away 500 points from a group
Group Challenge!
Countdown Numbers Game: https://incoherency.co.uk/countdown/game/numbers#google_vignette