Thermodynamics Flashcards
What happens when you add heat to a system?
Makes bonds easier to break, meaning they could change phases
At constant temperature theres a relationship between…
Volume and pressure, as volume decreases pressure increases.
pv=constant
At constant pressure theres a relationship between…
Volume and temperature, theyre directly proportional
v/t=constant
At constant volume theres a relationship between…
Pressure and temperature, theyre directly proportional
p/t=constant
Gasses with the same volume and pressure contain..
the same number of particles (avogradros law)
What is the energy of a gas stored as?
Random kinetic energy
How is kinetic energy calculated?
1/2mv2
How to calculate energy of a moles of gas?
3/2RT . Can use temperature since energy is related to temp
if you wanted per particle would use boltzmans instead of R
If you double the moles in a system what happens to pressure?
It doubles
What equation are all the gas laws linked by?
pv=nrt
The ideal gas equation…
pv=nrt
units of the ideal gas equation
pv=nrt
p= pascals v= m3 n= moles r= J.K. mol-1 t= Kelvin
in ideal gas equation what is pressure unit?
Pascals
In ideal gas law what is the unit for volume?
m3
how to convert from Celsius to kelvin?
+273.15
What are the assumptions of ideal gas law?
Atoms don’t interact with each other
Atoms are points and don’t have volume
Not a quantum system- they don’t have different shapes and sizes
Why does the ideal gas law only take into account moles of a gas not what type of gas?
Translational kinetic energy only depends on temperature
how do yo calculate total pressure?
The sum of all partial pressures
Why is pressure proportional to pressure?
The more particles colliding with the container the higher the pressure, all the collisions add together .
Why is deviation greater at higher pressures?
The atoms are closer together so they have more opportunity to interact
What is the absolute zero?
the temperature in which it could never get colder
where does the kelvin scale start?
At the absolute zero
What is a path function?
A value which depends on the route taken
What is a state function?
A value which doesn’t depend on the route only the current state
examples of path functions…
Heat, work
examples of state functions…
Temperature, pressure, Volume
Why are state functions important?
If we can prove something for a state function, it is always true for that state.
What is an extensive property?
Depends on the amount of thing (number of eggs needed to make a big or small cake) (if you add more iron to a clump volume will increase)
What is an intensive property?
Depends on the thing itself (ratio of eggs to flour, not the amount of eggs) (if you add more iron to a clump density stays the same)
What is energy?
the potential to do work. (the potential to cause change)
What is work?
Transfer of energy that causes directed motion against a force
What is heat?
Transfer of energy to cause random motion
What functions are work and heat?
Path functions
Equation for work/
w=F x dx
force(N) X direction (M)
Work (J)
Unit for work/
Joules (J)
unit for force
N
What is the system?
the bit of interest
What are the surroundings?
Everything else that isn’t system
What is the universe?
System+ surroundings
What are the four types of system?
Isolated, adiabatic, closed, open
In solids what motion do particles have?
Only vibrational
why are gasses compressible?
Most of a gas is empty space
As you increase pressure what happens to volume?
Decreases
How to convert litres to M3?
divide by 1000
How to convert cm3 to M3?
Divide by 1 X 10-6
What is an isolated system?
doesn’t interact with surroundings at all. neither energy nor matter
What is an adiabatic system?
One which can exchange energy through work, no matter exchanged
what is a closed system?
Can exchange energy in the form of heat or work, not matter
What is an open system?
Can exchange both energy and matter
What happens to internal energy (u) of an isolated system?
It remains constant (1st law)
what is internal energy (U)?
its the sum of many different energies within, eg translational, rotational, vibrational, electronic…
All these energies are intrinsic to the system no matter where it is or what its doing
Its a state function
What function is internal energy (U)?
State function, only depends on the state its in, not how it got there. All properties are intrinsic to the system, the don’t depend on where or what the thing is doing
What is U and is it measurable?
U= internal energy
No it isn’t measurable
What can we measure regarding U
the changes to U
What is the first law of thermos?
Internal energy of a system remains constant
Equation for change in internal energy in an isolated system?
dU= q+ W
q=heat
W= work
What is the only work an ideal gas can do?
Expansion work
How is the internal energy of an ideal gas stored?
in the motion of molecules (translational energy)
What do you measure to measure changes in U?
Changes in temperature
What does isothermal mean?
Constant temperature
For a gas to expand what does the pressure of the outside need to be?
Lower than inside
Equation for compression and expansion work of an irreversible, isothermal ideal gas at constant temp
w= Pexternal x (Vfinal-Vinitial)
For expansion work what is the sign?
Negative since the system does work
For compression of a gas what is the sign?
Positive since work is being done to the system
What does more expansion work, irreversible expansion or reversible expansion?
Reversible expansion
Equation for reversible isothermal expansion work of an ideal gas?
-nRT ln(Vfinal/Vinitial)
Differences between reversible and irreversible expansion work?
Reversible completes more work, reversible Pext is infinitesimally smaller than Pint whereas in irreversible Pext is constantly lower
If an ideal gas is kept at constant temperature what happens to dU?
= 0
since internal energy of an ideal gas only depends on translational energy which only depends on temp, so if this doesn’t change, neither will U
For an isothermal process what is dU?
0
No change in heat means no change in internal energy for an ideal gas (only has translational energy)
Equation for Enthalpy? (H)
H= U+ pV
what function is enthalpy?
A state function
What enthalpy is higher, to melt something or to boil it?
To boil it since you need to break all bonds, rather than some
When is more heat required to increase temp, at constant pressure or constant volume?
At constant pressure, since at constant volume the system if free to expand and do work
What is enthalpy called when you melt something?
Enthalpy of fusion
What is enthalpy called when you boil something?
Enthalpy of vaporisation
What is a negative enthalpy change?
Exothermic (system gives out heat)
What is a positive enthalpy change?
Endothermic (system takes in heat)
Is enthalpy positive or negative if endothermic?
positive (system takes in heat)
Is enthalpy positive or negative if exothermic?
Negative (system gives out heat)
For the same process running in opposite direction what is enthalpy?
Equal and opposite
