chem2 - 3qpt

Upload: alyssa-jane-boller

Post on 04-Apr-2018

213 views

Category:

Documents


0 download

TRANSCRIPT

  • 7/30/2019 Chem2 - 3QPT

    1/5

    -aysa. 12

    Ways of Expressing Concentration

    1. Molarity: Mi.

    2. Percent Solutionsa. Percent by volume

    i. x 100%b. Percent by mass

    i.

    x 100%

    c. Percent mass over volumei.

    x 100%

    3. Molality (mol/kg): mi.

    4. Mol fractioni.

    XA =

    *ppm = 1g of solute for 106g solution

    Intermolecular Forces and Liquids and Solids

    1. Phase a homogenous part of the system incontact with other parts of the system but

    separated from them by a well-defined

    boundary.

    o Solid phase iceo Liquid phase water

    2. Intermolecular Forces attractive forcesbetween molecules. Generally much weaker

    than intramolecular forces

    o Ex. 41 kJ to vaporize 1 mole of watero Measured by:

    Boiling point Melting point Hvap Hfus Hsub

    3. Intramolecular Forces hold atoms together ina molecule

    o Ex. 930 kJ to break all O-H bonds in 1mol of water

    Intermolecular Forces

    1.

    Dipole-Dipole Forces attractive forcesbetween polar molecules

    2. Ion-Dipole Forces attractive forces betweenan ion and a polar molecule

    3. Dispersion Forces attractive forces that ariseas a result oftemporary dipoles induced in

    atoms or molecules; usually increase with molar

    mass

    a. Polarizabilityi. the ease with which the

    electron distribution in theatom or molecule can be

    distorted

    ii. increases with greater numberof electrons and more diffuse

    electron cloud

    4. Hydrogen Bond a special dipole-dipoleinteraction between the hydrogen atom in a

    polar N-H, O-H, F-H bond and an

    electronegative O, N, or F atom.

    5. Ionic Bonding attractive forces between ions6. Dipole-Induced Dipole attractive forces

    between polar and nonpolar molecules

    Properties of Liquids

    1. Surface Tension amount of energy required tostretch or increase the surface of a liquid by a

    unit area.

    (intermolecular forces = surface tension)2. Cohesion the intermolecular attraction

    between like molecules

    3. Adhesion attraction between unlike molecules4. Capillarity rising of liquid through a narrow

    space against the pull of gravity

    5. Viscositymeasure of a fluids resistance toflow

  • 7/30/2019 Chem2 - 3QPT

    2/5

    -aysa. 12

    Phase Changes

    Equilibrium Vapor Pressure the vaporpressure measured when a dynamic equilibrium

    exists between condensation and evaporation

    o Dynamic Equilibrium: Rate of condensation= rate of evaporation

    Molar heat of Evaporation (Hvap) the energyrequired to vaporize 1 mole of a liquid

    a. Clausius-Clapeyron Equation:P = -

    P = equilibrium vapor pressure

    T = temperature in K

    R = gas constant (8.314 J/K-mol)

    Boiling Point the temperature at which thevapor pressure of a liquid is equal to the

    external pressure

    Normal Boiling Point the temperature atwhich a liquid boils when the external pressure

    is 1 atm

    Critical Temperature (Tc) the temperatureabove which gas cannot be made to liquefy, no

    matter how great the applied pressue

    Critical Pressure (PC) the minimum pressurethat must be applied to bring about the

    liquefaction at the critical temperature

    Melting/Freezing Point the temperature atwhich the solid and liquid phases coexist in

    equilibrium Molar Heat of Fusion (Hfus) the energy

    required to melt 1 mole of a solid substance

    Molar Heat of Sublimation (Hsub) the energyrequired to sublime 1 mole of a solid

    Phase Diagram summarizes the conditions atwhich a substance exists as a solid, liquid, or gas

    Colligative Properties of Solution

    - Properties of solution which depends on thenumber of solute particles & not on their

    chemical identity

    o Vapor Pressure Loweringo Boiling Point Elevation

    o Freezing Point Depressiono Osmotic Pressure

    1. Vapor Pressure Loweringo The vapor pressure of a solution of

    nonvolatile nonelectrolyte is always

    lower than the vapor pressure of pure

    solid. *vapor pressure: pressure

    needed to evaporate

    o Raoults Law: the vapor pressure ofsolvent above solution (Psolvent) equals

    the mole fraction of solvent in the

    solution (Xsolvent) multiplied by the vapor

    pressure of the pure element (Psolvent)

    Psolvent = (Xsolvent) (Psolvent)

    P = (Xsolute) (Psolvent)

    2. Boiling Point Elevationo A solution boils at a higher temperature

    than the pure solvent

    o vapor pressure = higher externalpressure

    Tb = (Kb)(m)

    Tb = Tb(solution) Tb(solvent)

    Tb = boiling point Kb = molal boiling point

    elevation constant

    o H2O: 0.512 m = molality

    3. Freezing Point DepressionTf= (Kf)(m)

    Tf = Tf(solvent) Tf(solution)

    Tf= freezing point Kf= molal freezing point

    constant

    o H2O: 1.86 m = molality

    4. Osmotic Pressure = MRT

    = osmotic pressure M = molarity R = 0.08206 T = temperature in K

  • 7/30/2019 Chem2 - 3QPT

    3/5

    -aysa. 12

    initial state

    final state

    initial state

    final state

    Colligative Properties of Electrolyte Solutions

    Vant Hoff Factor (i) - One way to measure the extent

    to which electrolytes dissolve

    - Count the number of ions in the compound

    (e.g. K2SO4: i= 3)i =

    *applied for electrolytes P, Tb, Tf

    Thermochemistry

    - Energy flow to and from the system- A system can be:

    o Open Change in mass Exchange of heat

    o Closed No change in mass Exchange of heat

    o Isolated No change in mass No exchange of heat

    Internal Energy, E

    - The sum of energies for all the particles in thesystem (Kinetic and Potential)

    - Immeasurable- in internal energy is immeasurable- E = Efinal Einitial = Eproducts- Ereactants- Change in E of system is always accompanied by

    an opposite change in the energy of the

    surroundings

    Efinal < EinitialEXOTHERMIC

    Efinal > Einitial

    ENDOTHERMIC

    *y axis: Energy

    Forms of Energy Transfer

    1. Heat (q) energy transferred as a result oftemperature difference

    2. Work (w) other form of energy transferTotal charge in systems internal energy is

    E = q + w

    Energy transfer as heat onlyo Heat flowing out of the system

    q is negative E is negative

    o Heat flowing into the system q is positive E is positive

    Energy transfer as work onlyo Work done by the system

    wis negative E is negative

    o Work done on a system wis positive E is positive

    Law of energy conversion

    - the total energy of the universe is constant

    (First Law of Thermodynamics)

    Euniverse = Esystem + Esurroundings = 0

    Units of energy

    1 J = 1 kg m2/s2 1 cal = 4.184 J 1 J = 0.2390 cal

  • 7/30/2019 Chem2 - 3QPT

    4/5

    -aysa. 12

    State Functions & the Path of Interdependence of

    Energy Change

    Energy is a state function, independentfrom the path

    o Dependent only on the currentstate of the system, not on the path

    the system took to reach the stateo E, P, V are state functionso q and ware not state functions

    Enthalpy Change

    H, change in enthalpy heat lost or gained

    during chemical change or physical

    change

    - H: exothermic

    +H: endothermic

    *qp: heat measured at constant pressure

    E = q + w

    *w: chemical work

    1. electrical work2. work done by moving particles3. PV work, expanding gas

    a. w= -PVFor reactions at constant pressure

    H = E + PV

    H = E + PV

    E = q + w

    = q - PV

    qp= E + PV

    qp= H

    *to get H, get qpqreaction = -qsolution

    Comparing E & H

    - in most cases, E H for reactions with little

    change in PV

    Reactions that do not involve gases

    1. Neutralization Reaction (V = 0)2. Reaction in which the amount (mol) of

    gas does not change

    3. Qp is much larger than PV

    Some Important Types of Enthalpy Change

    1. Hcomb = heat of combustion- when one mole of substance

    combines with O2

    2. Hf= heat of formation3. Hfus = heat of fusion- when one mole of substance melts

    4. Hvap = heat of vaporization

    - when one mole of substance vaporizes

    Calorimetry

    Specific Heat amount of heat required to raise

    temperature of 1g of substance by 1C

    Heat Capacity amount of heat required to raise

    temperature of object by 1C

    Specific Heat Capacity

    q = mcT

    Molar heat capacity (c) the quantity of heat

    required to change the temperature of 1 mole

    of a substance by 1C

    c =

    Calorimeter used to measure the heat released or

    absorbed by a physical or chemical process

    - serves as the surrounding

    1. Constant pressure calorimeter(coffee-cup)

    2. Constant volume calorimeter (bombcalorimeter)

    1. Constant Pressure Calorimetera. Open to the atmosphereb. Determination of specific heatc. Determination of heat of reaction

    2. Constant Volume Calorimetera. Given heat capacity of the entire

    calorimeter

    b. Designed to measure very precisely theheat released in a combustion reaction

    Indirect Determination ofH: Hesss Law

  • 7/30/2019 Chem2 - 3QPT

    5/5

    -aysa. 12

    1. H is an extensive property2. H changes sign when a process is

    reversed

    3. Hesss Law of constant heatsummation

    4. BASTA YUNG CANCEL-CANCEL. =))Easiest topic so

    Standard Enthalpies of Formation

    - standard state of solid of liquid substance is

    the pure element or compound at 1atm

    pressure & at temperature of interest

    Standard Enthalpy of Reaction, Hrxn

    - enthalpy change for reaction in which

    reactants & products are at standard

    states

    Hf of formation of a pure element in its most

    stable form is zero

    + Hf: formed by endothermic reaction

    H = vpHf (product) - vpHf (reactants)