CHEM 1C Final

Joseph S25

G

Gibbs Free Energy

∆G is positive

the reaction is nonspontaneous

the system gained energy to use

∆G is negative

the reaction is spontaneous

the system used its own free energy to do the reaction

S

entropy, measure of disorder or randomness within a system

∆S is positive

increase in disorder

ex: liquid to gas, the molecules are less structured

∆S is negative

decrease in disorder

ex: liquid to solid, the molecules become more structured

H

enthalpy, the internal energy of a system

∆H is positive

endothermic reaction, the system absorbed heat

∆H is negative

exothermic reaction, the system released heat

When is ∆G ALWAYS negative? (Spontaneous)

∆H = -

∆S = +

When is ∆G SOMETIMES negative? (spontaneous)

When ∆H and ∆S have the same sign

When is ∆G ALWAYS positive? (non spontaneous)

∆H = +

∆S = -

E_a

activation energy, the threshold energy that must be overcome to produce chemical reaction

Factors that affect rate

1. Nature of reactions

2. Reactant concentration/surface area

3. Temperature

4. Catalyst

rate equation

∆ concentration/time

units of rate

M/s or mol/L•s

rate law

rate = k[A]ⁿ

Differential rate law

based on concentration

Integral rate law

based on time

Pseudo order

where one reactant is at a much higher concentration than the other

Intermediate

a species that is produced in the reaction and then consumed

Collision theory

molecules must collide to react

Arrhenius equation slope

E_a/R

Arrhenius equation y-intercept

lnA

Homogeneous catalyst

present in the same phase as the reaction molecules

Heterogeneous

exists in a different phase as the reacting molecules

IMFs v. Boiling Point

direct relationship between the two; as IMFs become stronger, boiling point becomes higher

LDF and molecule/atom size

More electrons = greater LDF

Longer molecule = greater LDF

Capillary action

rising of liquid in a narrow tube

Cohesive force

attraction of molecules to each other

ex: H₂O molecules in water

Adhesive force

attraction of molecules to the walls of the capillary

ex: H₂O molecules sticking to the glass of a test tube

Why do liquids form spheres?

minimizes surface area:volume ratio because molecules at the surface don’t have as many interactions

Viscosity

resistance to flow because of strong IMFs and the largeness of molecules

Vaporization

liquid to gas

Condensation

gas to liquid

Melting

solid to liquid

Freezing

liquid to solid

Sublimation

solid to gas

Deposition

gas to solid

Do phase transitions occur at constant temperature or during temperature changes?

At constant temperature

Vapor pressure

partial pressure of evaportaed material

Relationship between vapor pressure and boiling point

High vapor pressure = low boiling point

more particles were able to evaporate because IMFs are strong (low boiling point)

Pressure v. Boiling Point

Higher pressure = higher boiling point

need more energy to overcome the force pushing down on liquid

Pressure and Volume

increasing P decreases volume

Triple Point

point on a phase change diagram where solid, liquid, and gas all coexist

Critical point

temperature and pressure above a certain point where it cannot be classified as a gas or liquid

Normal boiling point

temperature at 1 atm

What unit cell has cubic closest packing structure (ccp)?

Face centered cell (fcc)

What unit cell has hexagonal closest packing structure (hcp)?

Body centered cell (bcc)

Which is more dense when the slope between solid and liquid on the phase diagram is positive?

Solid

Solute

substance that is being dissolved

Solvent

the medium that the solute is dissolving in

Molality

moles of solute / kg of solvent

Solubility between “like” molecules

Very good

ex: polar solutes in polar solvents

Is a non-polar molecule soluble in water?

No it is not because water is polar. Like dissolves like alot better than polar and non polar.

Pressure v. Solubility

Increasing external pressure increases solubility

forces gas particles into solution

Temperature v. solubility for gas

Increasing temperature decreases solubility

Temperature v. Solubility for solids

increasing temperature increases solubility

Nonvolatile solutes and its effects on vapor pressure

adding nonvolatile solute lowers vapor pressure

blocks the way of solution evaporating

Vapor Pressure v. Boiling Point

High vapor pressure = lower boiling point

high vapor pressure means more things were evaporated, meaning lower boiling point

Negative Deviation

• Strong interactions between solute and solvent

  • Negative ∆Hsolution

• Psolution lower than expected

• mixture of like molecules

Positive Deviation

• weak interactions between solute and solvent

• P solution was higher than expected

• mixture of non-like molecules

Boiling Point Elevation

Boiling point increasing when a nonvolatile solute is added because it lowers vapor pressure

Freezing Point Depression

Freezing point decreases when a nonvolatile solute is added

Osmosis

semi-permeable membrane allows solvent to pass but not the solute particles to equilibrate concentrations

Osmotic Pressure

additional pressure that is needed to keep solution and pure solvent levels equal

a.k.a. prevents osmosis from happening

Hypertonic Solution

The solution that has a higher concentration of the solute

• water will flow towards the hypertonic solution

Hypotonic Solution

The solution that has a lower concentration of the solute

• water will flow out the hypotonic solution

What affects vapor pressure?

Temperature and the nature of the substance