Chem 2 Exam 1 Flashcards
What is an intramolecular force?
- Bonds within a molecule.
- Usually strong.
- Determine the chemical properties
What is an intermolecular force?
- Attraction between molecules.
- Usually weak.
- Determine the physical properties.
What are the types of intermolecular forces (IMFs)?
- London Dispersion Forces
- Dipole-Dipole Attraction
- Hydrogen Bonding
- Ion-Dipole Forces
What are London Dispersion Forces?
- Operate between all species (neutral, charged, polar, or nonpolar).
- Results from uneven distribution of electrons.
What do the strengths of London Dispersion Molecules depend on?
- Size of molecules (molar mass)
- Molecular shape (compact of elongated)
Effect of size on a large molecule (london dispersion)
Larger molecules —> more polarizable —> stronger london forces —> high MP, BP
Effect of size on small molecule (london dispersion)
Smaller molecules —> less polarizable —> weaker london forces —> low MP, BP
Compact molecular shape (london dispersion forces)
- more compact
- small area for interaction
- weaker london forces
- lower boiling point
Elongated molecular shape (london dispersion forces)
- less compact
- larger area for interaction
- stronger london forces
- higher boiling point
What is Dipole-Dipole Attraction?
- occur only in polar molecules, which contain permanent dipoles
- the positive end of one permanent dipole attracts the negative end of another through dipole-dipole forces
How to find polar molecules?
- different atoms asymmetrically attached to central atom
- only one lone pair on central atom
- lone pairs are asymmetrically placed around the central atom
What is Hydrogen Bonding?
- very strong special type of dipole-dipole interaction
- occurs between H and F, O, or N
What are Ion-Dipole Forces?
- Occurs when an ionic compound is mixed with a polar molecule
- ions are attached to the dipole of polar molecules
- higher the charge on ion, stronger ion-dipole interaction
- smaller size of ion, stronger ion-dipole interaction
IMFs from strongest to weakest?
- ion dipole forces
- hydrogen bonding
- dipole-dipole attraction
- london dispersion forces
What are the three properties that depend on the strengths of intermolecular forces?
- Viscosity
2 Surface Tension - Capillary Action
What is Viscosity?
measures a liquids resistance to flow
- ex. liquid with lower viscosity flow freely (water, gasoline,…) liquid with higher viscosity do not flow freely (honey, syrup…)
What factors affect viscosity and why
- Intermolecular Forces - stronger IMFs = higher viscosity
- Temperature - higher temp = lower viscosity
- Size and Shape of Molecule - large and complex structure = higher viscosity
What is Surface Tension?
The tendency of liquids to minimize their surface area.
- liquid beads to yield the minimum surface are (surface molecule interacts with 4 neighbors while interior molecule interacts with 6 neighbors)
What Factors Affect Surface Tension and Why
- Intermolecular Forces - stronger IMFs = higher surface tension
- Temperature - surface tension decreases as temp increases
What is Capillary Action?
The rise of liquid in a narrow tube (i.e.a capillary) immersed in the liquid
- due to attraction of the liquid molecules to the surface of the tube
- the attraction to the surface draw the liquid up tube
What is Solid to Gas Called and Vice Versa?
- Solid to gas = sublimation
- gas to solid = deposition
Vaporization
- liquid to gas
- endothermic process
- energy needed to overcome IMFs
- ∆Hvap always positive
What is ∆Hvap Heat of Vaporization?
the amount of heat required to vaporize one mole of a liquid to gas
Condensation
- gas to liquid
- exothermic process
- energy is released
- ∆Hcond always negative
∆Hcond = −∆Hvap
Rate of Vaporization Increases with….?
- Increasing Temp: average kinetic energy increases and more molecules have enough energy to over the IMFs
- Increasing Surface Area: the surface molecules are held less tightly, thus have greatest tendency to evaporate
- Decreasing Strength of IMFs: less attraction forces to hold molecules in liquid state
What is Dynamic Equilibrium?
Reciprocal processes are occurring at equal rates
- system at dynamic equilibrium: rate of forward reaction = rate of backward reaction
- occurs in closed systems where molecules cant escape
- the double arrow indicates dynamic equilibrium
What is Vapor Pressure?
pressure exerted by a vapor in equilibrium with a solid or a liquid at a given temperature in a closed system
What Affects Vapor Pressure of a liquid?
- Temperature
- IMFs
How does Temperature Affect Vapor Pressure?
At higher temps:
- molecules have higher thermal energy
- more molecules have enough energy to evaporate
- number of molecules in gas phase is higher
- vapor pressure is high
- INCREASING TEMPERATURE INCREASES VAPOR PRESSURE
How do IMFs Affect Vapor Pressure?
- Weaker IMFs —> high vapor pressure
- Stronger IMFs —> Low vapor pressure
What is Boiling Point?
Temperature at which liquids vapor pressure = the external pressure
- during boiling, temp is constant
- variations in atmospheric pressure will change boiling point (high altitude –> lower atmospheric pressure –> lower BP)
What is normal boiling point?
1 atm or 760 torr or 101.3 kPa
Effects of IMFs on Boiling Point
- weak IMF —> higher vapor pressure —> low BP
- strong IMF —> lower vapor pressure —> high BP
IMF, Rate of Vaporization, Vapor Pressure, and BP
- Weak IMF —> Higher rate of vaporization —> high vapor pressure —> low boiling point
- Strong IMF —> lower rate of vaporization —> low vapor pressure —> high boiling point
What does each symbol stand for in ln(P2/P1) = -∆𝐻vap/R (1/T2 - 1/T1) ?
- P1 = vapor pressure at temp. 1
- P2 = vapor pressure at temp. 2
- ∆𝐻vap = heat of vaporization (J/mol)
- R = gas constant, 8.314 J/mol x K
- T1 = temp. 1 in kelvin
T2 = temp. 2 in kelvin
What is a phase diagram?
Pressure(y) - temperature(x) graph
- shows the effects of both pressure and temp. on phase changes
- Three main regions: solid, liquid, gas
What is Triple Point (phase diagram)?
temp. and pressure where 3 phases coexist in equilibrium
What is Critical Point (phase diagram)?
highest temp. and pressure at which a pure material can exist in gas/liquid equilibrium
- CRITICAL POINT IS ALWAYS HIGHER THAN TRIPLE POINT
What is Supercritical Fluid?
substance at a temp. and pressure above its critical point and density near its liquid density
- have properties between those of gas and liquid
What is a solution?
homogenous mixture of two or more substances
- solution = solvent + solute
What is a solvent?
the component present in high concentration
- water is solvent —> aqueous solution
What is a solute?
the component present in low concentration