gchem 2 Flashcards
What is convection?
fluid movement caused by hotter portions of a fluid rising and the cooler portions of the fluid sinking
What is radiation?
electromagnetic waves emitted from a hot body into the surrounding environment
What is a black body radiator?
theoretically perfect body that absorbs all energy incident upon it and emits 100% of this energy as electromagnetic radiation
What is conduction?
molecular collisions carry heat along a conduit
What is heat capacity?
the amount of energy a system must absorb to give a unit change in temperature (J/K or cal/degrees celcius)
What is the formula for heat capacity?
C = q/∆T
What is the formula for specific heat?
q=mc∆T
What is the specific heat of water?
1.0 cal/g ̊C
What is the purpose for calorimeters?
To calculate enthalpy change
How to solve coffee cup calorimeter problems
q=mc∆T
How to solve bomb calorimeter problem
q = C∆T
Which type of calorimeter provides constant pressure and which provides constant volume?
bomb -constant volume
coffee- constant pressure (atmospheric)
What is pressure - volume work?
change in volume at constant pressure
On a pressure vs. volume graph, what represents the pv work?
The area under the curve
What is the first law of thermodynamics?
energy can neither be created or destroyed
work done on the system is ___, work done by the system is ___
positive, negative
What is the second law of thermodynamics?
heat cannot be changed completely into work in a cyclical process
entropy in an isolated system can never decrease
What is the third law of thermodynamics?
pure crystalline substances at absolute zero have an entropy of zero
What is the zeroth law of thermodynamics?
everything tends to move toward thermal equilibrium with everything else. (2 objects in thermal equilibrium = same temperature)
What is the definition for temperature?
the average kinetic energy of molecules
What equation shows the direct relationship between temperature and kinetic energy?
KE = 3/2kBT (where kB is Boltzmann’s constant)
How to convert celcius to Kelvin
add 273.15 to celcius
What is enthalpy?
the energy contained within chemical bonds
What is standard state?
a set of specific conditions as the reference point for measuring and reporting enthalpy, entropy, and Gibbs free energy
How to calculate ΔHRXN Using Bond Energies
add up the bond energies of all of the products and reactants. If a bond is broken during the reaction, energy is required, so the bond energy should be given a positive sign. If a bond is formed, energy is released, so the bond energy should be given a negative sign. Once again, multiply all bond energy values by their coefficients in the balanced equation.
ΔHcombustion
A high heat of combustion is associated with an unstable molecule and a low heat of combustion with a stable molecule.
ΔHformation
The enthalpy value for the formation of a compound from its elements in their standard states. If the number is negative, formation is an exothermic process, if it is positive, the process is endothermic.
ΔHsolution
The enthalpy value associated with the dissolution of a species into solution. We’ll discuss this in more detail when we cover solution chemistry.
ΔHvaporization
The enthalpy value associated with the phase change from liquid to gas. The reverse process (condensation) simply interchanges products and reactants and thus the sign is just changed.
ΔHfusion
The enthalpy value associated with the phase change from liquid to solid. The sign changes for the reverse process (melting)
What is entropy?
a measure of randomness or disorder in a system
Entropy increases with 5 factors increasing?
number of items, volume, temperature, disorder, complexity
What is gibb’s free energy?
∆G = the amount of “free” or “useful” energy available to do work
What does isobaric mean?
constant pressure
What does isothermal mean?
no heat exchange
What is the fundamental thermodynamic relation?
∆G = ∆H - T∆S
If ∆H is positive and entropy change is negative, what will the sign of ∆G be?
positive
If the change in entropy is positive, and enthalpy is negative, the reaction is :
spontaneous
If a reactant is dissolved in a solution, causing the temp to increase, the ΔG for this reaction is __
negative
What equation relates Gibbs free energy to equilibrium?
∆G° = - RTlnKeq
Keq = e^ -ΔG/RT
Arrhenius acid/ base definition
acids- produce H+ ions in solution
base- produce OH- ions in solution
Bronsted Lowry acids/bases
acids - donate protons
bases - accept protons
Lewis acid/bases
acid - accept pair of electrons
base- donate pair of electrons
What is the definition of amphoteric ?
substances can act as either an acid or base
eg H2O
Calculate pH with H+ concentration
pH= -log (H+)
What is the equation for Kw?
Kw=[H3O+][OH-]=10^ -14
Formula for acid dissociation constant
Ka = [H+][A-]/[HA]
If Ka is greater than one, that means the acid is __
strong
What is the formula for base dissociation?
Kb = [OH-][HA]/[A-]
Smaller Kb indicates that an acid is __
strong
Addition of either an acid or base to water shifts the equilibrium for the ionization of water to which direction?
left
How to calculate the pH for weak acids
- write out balanced eq
- ICE table
- solve for x
- -log(H+)
all strong acids and bases dissociate __ percent in water
100
What are the strong acids?
HI, HBr, HCl, HNO3, HClO4, HClO3, H2SO4, h3O+
What are the strong bases?
Group 1A hydroxides, NH2-, H-, Ca(OH)2, Sr(OH)2, Ba(OH)2, Na2O, CaO
If an acid has a Ka less than 1, than it is __
weak
If a base has a Kb less than one, it is a ___ base
weak
What does the “salt of a weak acid” refer to?
conjugate base of the weak acid combined with a cation
What does the “salt of a weak base” refer to?
conjugate acid combined with an anion to form a salt
What does the term “equivalent” mean when it comes to titration?
the amount of acid or base necessary to produce or consume one mole of [H+] ions
On a titration curve, what is one the x-axis and what is on the y-axis?
x-axis - volume of titrant
y-axis - pH
What is the difference between an analyte and a titrant?
analyte - in beaker
titrate - added dropwise
For SA and SB, at the equivalence point, ____
[H+] = [OH-]
At the equivalent point/stoichiometric point, the [titrant]= __
[analyte]
What is the pH of the equivalent points for WB w SA, WA w SB, SA w SB, WA w WB?
For WB w/ SA: pH < 7
For WA w/ SB: pH > 7
For SA w/ SB: pH about 7
For WB w/ WA: pH about 7
half equivalence point = ____ on graph
midpoint of nearly horizontal section
at half equivalence point, [HA] ___
[HA] = [A-]
What are indicators?
weak acids that change color as they dissociate. To set up a titration, you should know the approx. pH of equivalence point to select an indicator that will change color at that pH
Difference between the end point and equivalence point?
end point - when indicator causes color change
equivalent - when [titrant] = [analyte]
Where is the buffer region?
nearly horizontal area surrounding the half-equivalence point
What is the Henderson -Hasselbalch equation?
pH = pKa + log[A-]/[HA]
