PHYSICAL EQUILIBRIA Flashcards
What type of reaction occurs going up a phase transition graph?
Endothermic
What is dH of an endothermic reaction?
dH > 0
What is an endothermic reaction?
Endothermic reactions gain heat through abdorption
What type of reaction occurs going down a phase transition graph?
Exothermic?
What is dH of an exothermic reaction?
dH < 0
What is an exothermic reaction?
Exothermic reactions become cooler through the release of heat
What is dH and dS of condensation?
Gas → liquid
dH < 0 ; dS < 0
What is dH and dS of vaporization?
Liquid → gas
dH > 0 ; dS > 0
What is dH and dS of freezing?
Liquid → solid
dH < 0 ; dS < 0
What is dH and dS of fusion?
Solid → liquid
dH > 0 ; dS > 0
What is dH and dS of deposition?
Gas → solid
dH < 0 ; dS < 0
What is dH and dS of sublimation?
Solid → gas
dH > 0 ; dS > 0
In what order does enthalpy (S) increase?
S(s) < S(l) < S(aq) < S(g)
Why does enthalpy increase going up a phase transition graph?
Enthalpy increases as attractive interactions between molecules decreases
In what order does entropy (H) increase?
H(s) < H(l) < H(aq) < H(g)
Why does entropy increase going up a phase transition graph?
Because there are more potential microstates for distributing the energy
What controls the balance between entropy (H) and enthalpy (S)?
Temperature
Which dominates at a lower temperature?
Enthalpy (S)
Which dominantes at a higher temperature?
Entropy (H)
At any given temperature, the most stable substance has the lowest ______?
Free energy
What do straight lines indicate on a phase transition graph?
Straight lines indicate a phase change (dG = 0; equilibrium)
How does temperature stay constant during a phase change?
Energy is able to flow in and increase the potential energy due to the formation of a new state after the breaking of IMFs, and NOT increase the kinetic energy
What do slopes indicate on a phase transition graph?
Slopes indicate that there is no phase change
What happens when there is no phase change?
Temperature increases because energy flows into the system as heat
How is the slope on a phase transition graph related to heat capacity?
Slope is inversely related to heat capacity
What is a phase diagram?
Phase diagrams show regions of stability of different phases as a function of temperature and pressure
What is triple point?
triple point is where all 3 phases are at equilibrium (dG = 0)
What is critical point?
Critical point is where both the liquid and gas phases of a substance have the same density and are therefore indistinguishable
What is vapor pressure?
Vapor pressure is the partial pressure of a substance at equilibrium with a condensed phase (liquid/solid)
What happens to molecules in an open container?
They diffuse into the room and out of the atmosphere, and eventually all will evaporate
What happens to molecules in a closed container?
Those that evaporate will diffuse around in the gas phase, but some will collide with liquids
What is the difference of kinetic energies between gas and liquid molecules?
Nothing, they have the same KEs because they share the same temperature
How is vapor pressure related to boiling point?
Vapor pressure is inversely related to boiling point
How is vapor pressure related to temperature?
Vapor pressure is directly related to temperature (exponentially)
What is the Clausius-Clapeyron Equation?
What is a solution?
A solution is a homogeneous mixture composed of a major component (solvent) and a minor component (solute)
Why are the IMFs of the solvent very similar to the pure substance?
Because each solvent molecule is surrounded bu other solvent molecules
Why are the IMFs of the solute very different to the pure substance?
Because the solute is completely surrounded by solvent
What is dG in a mixture?
dG < 0
Why is mixing 2 gases spontaneous?
Because either the enthalpy (S) goes down or entropy (H) goes up
What is dS in a mixture?
dS > 0
What is dH in a mixture?
dH is constant (dH = 0) because ideal gases have no IMFs, therefore no PE
What is dH for a solution?
How are interactions altered in a solution?
Solute-solute interactions are lost and solute-solvent interactions are gained
What is dH lattice energy usually described as?
A positive number because energy is inputed to pull solutes apart
What is dH solvation usually described as?
A negative number because E is released when the solute ineracts with the solvent
When will a substance dissolve?
When a solution is formed, dH solutions > 0 and dS solutions > 0
However, like dissolved like to minimize dH solutions, where TdS solutions > dH solution
What is Henry’s Law?
The mole fraction of the dissolved as in liquid is directly proportional to the pressure of the gas over the liquid; used to determine the solubility of a gas in a liquid
When is a solution more stable?
A solution is more stable over a wider temperature range
What are colligative properties?
Colligative properties are properties of a solution that depend on a particular solvent and the concentration, but they do not depend on the chemical nature of the solute
What are the 4 colligative properties?
- Vapor pressure lowering
- VP solution < VP pure substance
- Boiling point elevation
- BP solution > BP pure substance
- Freezing point depression
- FP solution < FR pure substance
- Osmosis
- Solvent moves to solution side because it is lower in free energu
What is the Van’t Hoff Factor (i) of a non-electrolyte (covalent bonds)?
1
What is the Van’t Hoff Factor (i) of a strong electrolyte (salts)?
Number of ions in the formula
What is the Van’t Hoff Factor (i) of a weak electrolyte?
More than 1 but less than 2
What is the main effect of vapor pressure lowering?
Entropy (H)
dS solution > dS pure substance ; dG solution < dG pure solvent
What is Raoult’s Law?
P° = VP of the pure solvent
Mole ratio = mole solvent / mole solution, where more moles of solute = smaller mole fraction = lower vapor pressure
What is the formula used for boiling point elevation?
m = total solute concentration in molality (moles solute / kg solvent)
What is the formula used for freezing point elevation?
m = (moles solute / kg solvent)
What does an increase in solution concentration do to free energy?
Decreases dG
What does an increase in solution pressure do to free energy?
Increases dG
What triggers the end of osmosis?
When dG on both sides are equal
How is osmotic pressure calculated?
What happens when the solute is a salt in a spontaneous dissolution?
dH = dH LE + dH solvation, where…
- dH LE > 0 and dH solvation < 0, so dH solution ~0
- dG < 0 because spontaneous
- dS > 0 because solid → aqueous species
- An increase in T increases solubility
What happens when the solute is a gas in a spontaneous dissolution?
dH solution = dH LE + dH solvation, where…
- dH LE = 0 and dH solvation < 0, so dH solution < 0
- dG <. 0 because spontaneous
- dS < 0 because gas → aqueous species
- An increase in temperature decreases solubility
What happens when the solute is a liquid in a spontaneous dissolution?
dH solution = dH LE + dH solvation, where…
Like dissolves like (dH~0)
What factors influence vapor pressure?
Temperature and identity
* Amount and volume don’t matter
How are vapor pressure and IMFs related?
VP and IMFs are inversely related
What do solid lines indicate on a phase diagram?
Similar free energies
What is dH when solute-solvent IMFs are stronger?
dH > 0 (endothermic)
What is dH when solute-solute IMFs are stronger?
dH < 0 (exothermic)
What happens when a solution is made?
- Entropy (S) increases
- Free energy (G) decreases
- More stable than corresponding liquid
How do you calculate molarity?
Molarity = moles solute / L solution
How do you calculate molality?
Molality = moles solute / kg solvent
How do you convert between molarity and molality?
Density
What are freezing point and boiling point dependent on?
The total number of solute particles (concentration x # particles), NOT the identity
