chem II partial 2 Quiz 3 Flashcards
Thermal dynamics
1st law conservation of energy: The more heat the more internal energy the more energy change
Energy is never lost it only transforms.
2nd law hess’s law: the overall enthalpy change of a reaction is equal to the sum of enthalpy changes for individual steps in the process
Calculating heat
.Equals molar heat capacity/specific heat times change of temperature times moles
If heat is positive the it is endothermic and if it’s negative it is Exothermic
Molar heat capacity
How much energy you must add to increase one mol (joules/mol times kelvin)
Different from specific heat
When there’s no interaction it depends in the #of particles, it’s about them and not about the substance
Enthalpy and where dos it come from
All energy available to be released as heat or absorbed
Change of internal energy(U) equals heat plus work which then elaborates all the way to heat equals (final internal energy plus final pressure times volume) [this is enthalpy ] minus (all in first
parenthesis but starting)
We can’t know the enthalpy of a substance at any point, there are two values but I don’t know their magnitude and if there is no work all energy will be transferred as work. If no work (compression and expansion of gases) then the
change of enthalpy equals the
heat. Calorimeter measures the heat transferred.
What affects enthalpy?? And standard thermal conditions
Pressure temperature and amount
1 atmosphere of pressure, 25 degrees Celsius and one mol
Different symbols of enthalpy changes
H with accent of house: molar enthalpy change: energy (molar heat capacity times temperature) difference for only one mol
H with nothing: total enthalpy change for cooling/hearing: energy difference of a pure substance when cooled or heated (heat formula)
H with reaction: total enthalpy change of the reaction: energy difference between the reactants and the products
H with degree and reaction: standard enthalpy change of the reaction: when TD conditions are met and under supposed state
H with degree and c: standard enthalpy change if combustion: same as above but for only combustion
H with degree and f: standard enthalpy of formation: when one mole of any substance is made through pure elements. And it’s the energy difference too.
The enthalpy of formation sum method
Hess law
Standard Change of enthalpy of reaction=enthalpy product minus enthalpy reactant. When you have a pure element that meets the state condition then it’s enthalpy is zero.
Sum of reaction(enthalpies summed for final enthalpy)
Lots of enthalpies to get to the final enthalpy
You can invert and multiply the reaction but also the enthalpy.
And make sure it is the equation you want
Chemical kinetics
You calculate the rates and speeds with time, heat, stoichiometry, etc. it involves almost everything a rate most of the time is something per time. In a graph of moles over time, the reactants decrease and the products increase. Not linear rates, only in a specific time.
Formula for the rate of reactants
-1( change of reactant on moles/change in time)
Formula for the rate of products
change of products on moles/change in time
Formula
For the overall rate of a reaction
Same formula only dividing by coefficient also
change of reactant on moles/change in time times coefficient
-1( change of reactant on moles/change in time times coefficient)
Factors that affect rate
Catalyzer(1), if yes then faster if no then normal
Temperature, surface area, concentration(2) and pressure(2) if they there is more if them then the reaction is faster if there is less then it’s slower
Although pressure is mainly for reactions with gases
What is pressure?
Pressure is force per unit area, newtons per cubic centimeter. It is a vector, it is a magnitude and it has a direction.
Weight is a force and it’s proportional to the mass.
What is atmospheric pressure? And experiment of barometer
The atmospheric pressure is maximum at sea level. The pressure the atmosphere applies to everything.
What pressures mercury to go up? Well the atmospheric pressure of course! And if you go further away from sea level, the less pressure the less mercury is pulled up.
Pressure units all of them
Pa pascals n/cm^3
Psi pounds per square inch for tires
ATM atmospheric or meteorological pressure
Mm hg or Torricelli(torr) for chemistry and blood pressure
Bar which is barometers
Law of Dalton’s partial pressure
The identity of the particle of the gas doesn’t matter and hence we can add the pressure of different gases to get the total pressure.
Collecting gas of a reaction in water
We have a mixture of that gas and water vapor. We know the total pressure and the pressure of water vapor at a certain temperature we can get the pressure of that gas o:
Standard temperature of pressures of standard things for a measuring a gas
1 ATM of pressure and 0 degrees Celsius
Gas properties (5…6)
•Gases exert pressure( they apply force because they crash into things)
•Gases completely fill a container, they diffuse( they distribute through the container because they move everywhere in chaos and randomly)
•compressibility, they are compressible( their volume can be reduced, lots of distance between them)
•low density(little mass of large volume, lots of distance again)
•gases are fluids( whatever shape you give them they can flow through it, move around objects and take various shapes because there’s enough space between then and nothing to stop them)
And maybe… They have indefinite shape
Boyle’s law
If there’s an increase in the force there’s an increase of pressure. PV=k
When pressure increases the volume is less and when pressure decrease the volume is more they are inversely proportional. And Boyle’s law says that P1V1=P2V2 only if the temperature is the same
Charles’s law
Relationship between V and T is linear or proportional when you have a constant pressure. And since V/T=k then, V1/T1=V2/T2
And the operation is always done in kelvin
Gay-lussac’s law
More T , more P in a closed space which means that volume is constant. They are directly proportional. P1/T1=P2/T2
Temperature
Average kinetic energy in particles
Heat
The transfer of kinetic energy
