Thermodynamics- 2 Flashcards
can internal energy be calculated
the actual value of internal energy cannot be calculated as some of the properties involves in its calculation cannot be measured such as electronic energy, nuclear energy etc.
However, change in internal energy can be calculated when the state of system changes from one to another which isneeded.
what is internal energy
The energy stored within a system is called as its internal energy. It takes into considered various energy such as electronci energy, nuclear energy, chemical bond energy, kinetic energy etc and so on.
why is internal energy a state function
Becaue its value depends only upon the final and initial states of the system and does not depedn on the path/method by whcih the state has been attained.
For example, consider a system which has water places in a thermos flask or insulated beaker. The internal energy can be changed in two ways
- doing mechanic work- using rotating paddle
- doing electronic work- using an electric immersion rod
the amount of work done is the same irrespective of the method through which it was done and produces the same change in state.
Explain the sign of internal energy
dU will be +ve if energy is absorbed by the system
dU= U2-U1 ( U2>U1)
dU will be -ve if energy is released by the system
dU=U2-U1( U1<U2)
is internal energy extensive or intensive
it is an extensive property, it depends upon the quantity of substance.
what is dU in isothermal reactions
the dU in isothermal reactions is 0 beause U2-U1
what is the sign of work
Work done is +Ve if work is done on the system
Work done is -ve if work is done by the system
what is the sign of heat
sign of heat is +ve if heat is absorbed by the system
sign of heat is -ve if heat is lost by the system to the surroudnings
state 1st law of thermodynamics
The energy of an isolated system is constant. Energy is neither created nor destroyed it is only converted from one form to another.
are q and w state functions? what abt q+w?
For a given change in state, q and w can
vary depending on how the change is carried
out. However, q +w = ∆U will depend only on
initial and final state. It will be independent of
the way the change is carried out. If there is
no transfer of energy as heat or as work
(isolated system) i.e., if w = 0 and q = 0, then
∆ U = 0.
what is the internal energy for an ideal gas
internal energy of an ideal gas is a function of temperature. So an ideal gas, undergoing an isothermal change, dU=0
q+w=0
q= -w, the work done i,by ststem equal to the heat absorbed by the system
what is the dU for adiabatic change
q=0
dU= Wₐd
what is enthalpy
It is th eheat content of a system. Enthalpy change of a system is the heat absorbed or evolved in a system at constant pressure.
sum of increase in internal energy and pressure volume work done
another way of definign internal energy
change in internal energy is the heat absorbed or evolved at constant volume
what are the conditions where deltaH = deltaU
-if the ractions is carried out in a closed vessel and volume remains a contant
- if theere are no gaseous reactants or products, only solids and liquids
- if the moles of gaseuous reactnats and products are equal on both sides of the reaction
