IMFS
Define London dispersion forces.
- present in all molecules and atoms
- important in non-polar molecules
- mostly among noble gas atoms and nonpolar molecules
- weakest IMF
What is a phase diagram?
Recognizes the physical states of a substance based on temperature and pressure
Define crystalline solids
A solid with particles are arranged in a regular, repeating pattern.
Ex. metals & ionic compunds
What role does electronegativity play in molecular polarity?
A higher electronegativity difference between atoms creates polar bonds. Small or no differences lead to nonpolar bonds.
How many grams of LiOH are needed to make 25 g of a 4.0 % solution?
0.04(25g) = 1.0 g
Whats weaker, IMFs or chemical bonds (intramolecular forces)?
IMFs
What is a triple point on phase diagram?
All 3 phases can coexist simultaneously
What typically makes a crystalline solid keep its shape?
The IMFs between the particles that make up the solid.
Is CH₄ (methane) polar or nonpolar?
Nonpolar, because even though C-H bonds are slightly polar, the tetrahedral symmetry cancels out dipoles.
0.100 mole of NaCl is dissolved into 100.0 grams of pure H2O. What is the mole fraction of NaCl?
100.0 g / 18.0 g mol¯1 = 5.56 mol of H2O
Add that to the 0.100 mol of NaCl = 5.56 + 0.100 = 5.66 mol total
Mole fraction of NaCl = 0.100 mol / 5.66 mol = 0.018
Name the 4 types of IMFs we discussed in class.
Ion-Ion, Hydrogen Bonding, Dipole-Dipole, London Forces
What is a change from a solid to a gas?
Sublimation
ex: dry ice
Describe ionic solids
- High melting points and boiling points due to strong forces
- Crystals are brittle and rigid
- Good conductors of electricity when dissolved in water, not as a solid
-Composed of positive & negative ions held together by electrostatic attractions
-Attractions between full charges are larger than partial charges
Why is NH₃ (ammonia) polar, but BF₃ (boron trifluoride) is nonpolar?
NH₃ is polar due to its trigonal pyramidal shape (lone pair on N). BF₃ is nonpolar because of its trigonal planar symmetry, which cancels dipoles.
A liquid solution contains 2.50 moles of glucose (C₆H₁₂O₆) dissolved in 750.0 g of water. Given that the vapor pressure of pure water at 25°C is 23.8 mmHg, calculate the boiling point elevation of the solution (Kb for water = 0.512°C·kg/mol).
Boiling point = 101.71°C
Explain surface tension and its relation to intermolecular forces.
The resistance of a liquid to increase its surface area. Liquids with high intermolecular forces (polar molecules) have a relatively high amount of this.
When does a supercritial liquid form?
When a substance is heated and pressurized beyond its critical point.
Describe metallic solids
- High melting and boiling points
- Malleable and Ductile
- Conduct electricity
- Structure often described as uniform with a sea of delocalized electrons
Would CO₂ or SO₂ be more soluble in water? Why?
SO₂ is more soluble, because it is polar, while CO₂ is nonpolar and does not interact strongly with water.
A gas has a solubility of 2.45 g/L at a pressure of 0.750 atm. What pressure would be required to produce an aqueous solution containing 6.25 g/L of this gas at constant temperature?
( 6.25 g/L x 0.750 atm )/2.45 g/L = 1.91 atm
Explain viscosity and its relation to intermolecular forces.
This is the measure of a liquid's resistance to flow. Liquids with large intermolecular forces are very highly this way.
What is a change from a gas to a solid?
Deposition
ex: snow forming in clouds
Differentiate between crystalline and amorphous solids.
Crystalline Solids
Amorphous Solids
Non-polar liquids are miscible in?
Non-polar liquids
Heating Curve of Water
Given Information:
- Mass of ice: 50.0 g
- Initial temperature: -10°C
- Final temperature: 120°C
- Specific heat capacities:
- Ice: c = 2.09 J/g°C
- Water: c = 4.18 J/g°C
- Steam: c = 2.01 J/g°C
- **Enthalpy of phase changes:**
- Fusion (ΔH_fus): 334 J/g
- Vaporization (ΔH_vap): 2260 J/g
Final Answer: 153.7 kJ
Q_total = 1045 + 16700 + 20900 + 113000 + 2010