Chapter 2: The First Law Flashcards
The total energy of a system is..
constant
open system
matter can be transferd
can exchange energy
closed system
matter can not be transfered through a boundary
can exchange energy
can transfer energy to the surrounding if they are at a lower temptaure
isolated system
neither energy ot matter can be transfered
energy trasnfer making use of thermal motion in the surrounding
work
is done to achive motion aginst an opposing force
the transfer of energy that makes use of orgainzed motion in the surroundings
energy
the capacity to do work ,if you are able to move against an opposing force then you can do work
compression in creases the capacity to do work , i.e. the energy of the system is increased . i.e work is done on the system
when work is done on the system the energy of the system increases and its capacity to do work is increased
when the system does work , the energy of the system decreases and the systems capacity to do work is decreased
heat
when the energy of a system changes as a result of temperature difference between the system and its surrounding, the energy has been transfered as heat
heat is a process ( the transfer of energy as a result of temperature difference ) , not an entity
diathermic
boundaries that permit the transfer of heat as energy
exothermic process
releases hate to the surrounding
▲H<0
adiabatic
boundaries that do not permit the transfer of energy as heat
endothermic process
energy is aquired from the surrounding as heat
energy is tranferd as heat to the system from the surroundings
▲H > 0
thermal motion
the disorderly motion of molecules
heating is the transfer of energy that makes us of disorderly, random, molecuar motion in the surroundings
internal energy
total energy of a system ( kinetic + potential energy)
∆U = Uf -Ui
dU = dq + dwexp + dwe
state function
depend only on the curren state of the systen and is independt of how that state has been prepared
path indepedent
extensive property( depends on the amount of substance
measure in joule: 1 J = kg m2 s-2
molar internal energy (Um = U/n) is an intensive(indepednt of amount) property
First Law of thermaldynamics (2A.2)
▲U = q +w
expansion work (2A.5a) (2A.6)
work arising from change in volume
neg cahnges in volume (compression)
dw = -pex dV
Pa m3
w = -pex▲V (constant pressure)
free expansion
expanson against zero opposing force
pex = 0
w = 0
vacuum
reversible expansion (2A.8a)
dw = - pex dV = - pdV
calorimetry
the study of the energy tranfer as heart during physical and chemical processes
calorimeter
a device used to energy transfer as heat
adiabatic bomb calorimeter
qv is measued
q = C▲T
where C is the calorimeter constant
heat capacity (2A.14)
slope of internal energy vs, tmeperature
Cv = (∂U/∂T)v
molalr heat capacity Cv,m = Cv /n
specifit heat capacity Cv,s = Cv/m
where m is mass
Cp = (∂H/∂T)p
enthalpy
H = U + pV
state function
increase with temp
▲H = qp = Cp▲T
perfect gas: H = U + pv = U + nRT
perfect gas , isothermal:▲H = ▲U + ▲ngRT
standard state
of a substance at aspecified temperature is its pure form at 1 bar
standard enthalpy of transition of vaporixation
standard enthalpy of fusion
Born-Haber Cycle
thermochemical equation
standard reaction enthalpy
▲rH⦵ =Σ vHm⦵-ΣvHm⦵
Hess’s Law
the standard enrhalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which a reaction may be divded
Standard Enthalpy of Formation
Mean bond enthalpies
Path Function
isenthalpic
internal pressure
Joule-Thomson effect
a process does work if ….
in principle it can be harnessed to rise a weight someeher in the surrounding
ex. expansion of a gas , the motion of the pistion be used to raise a weight
an endothermic process in a diathermic contaniner
(a boundary that does perrmit the tranfer of energy as hate)results in energy flowing into the system as heat to restore the temperature to that of the surrounding
a,) energy enters as heat from the surrounfoundings , and the system remains at the same temp(isothermal)
an exorhernic process in a diathermic container results in
a release of energy as heat to the surroundings
energy leaves as hate and the process os isothermal
exothermic process in a adiabatic container
the rise in temp
endothemic process in a adiabatic system
the temperature falls
why is the distincation of work and heat made in the surrounding
it is a refercne point
compression : the order atom of the weight(surroundings) creates random motion in the system( an increased in thermal motion)
we observe, the orderly decent of atoms and report that work is being done even though it is stimulating thermal motion
What are the modes of motion
tanslational
rotate
vibrate
equipartition theorem
can be used to predict the contribution of each mode of motion of a molecule to the total energy of a collection of non interacting molecules
translational and rotational modes of motion are porpportional to temperature
i.e internal energy incres with temp
the internal energy of a perfect gas is
independent of the volume it occupies
i.e. there aare no intermoleacular interactions in a perfect gas, so the distance between the molceules has no effect on the energy
heat and work are equalent was of
transering internal energy
in an isolated system intenal energy is (first law of thermodynamic )
constant
▲U = q + w
q- energy transfered as heat =0
w-work =0
the change in internal energy is equal to the energy that passes throught its boundary as heat or work
sign of ▲U
pos if heat or work enter the system
neg, if energy is transferd out aas heat or work
isothermal expanson of a perfect gas
w = -nRT dV/V = -nRTlnVf/Vi
Heat transfered at constant volume
dU = dq
no expansion work
▲U = qv
internal energy at constant volume
▲U = qv = Cv ▲T
a change in enthalpy is equal to
the energy transfered as heat as constant pressure
relation between heat capacties
Cp - Cv = nR
