Thermo 2 Energy Flashcards
What are the forms of energy
Heat
Kinetic
Gravitational
Electrical
Chemical
Explain the story of energy
Toddler had 10 block and the blocks can’t leave the room
Go in the room only find 9 blocks
Has a bucket of water and you feel the block sliding inside it
Can tell where the block went
Energy is our way of keeping track of something, if it goes missing we can figure out where it went and change it back into something else
Explain the energy conservation equation and what it tells us
Tells us that energy is conserved
Delta U = Q + W
The change it the internal energy of the system = the heat and the work
In heat and work we look at how energy is transferred between the two
What is Q
What is W
Heat
When there is energy transfer between the system and the surroundings as a result of temp difference
Work
Can be mechanical chemical or electrical
Happens when a force acts over a distance against an opposing force
What are the three types of systems
What do they mean
Isolated
Can’t exchange particles or energy with anything else
Closed
Can exchange energy but not particles, so no mass transfer
Open
Can exhange energy and particles
Explain the equilibrium conditions
Have two materials and a moveable or immovable wall between them
If immovable and we allow heat transfer, the temperature will reach equilibrium
If moveable and we allow heat transfer, the pressure and the temp will reach equilibrium (wall will move until the pressure is the same in bother materials)
If the wall is porous, the temp, pressure, and chemical potential will reach equilibrium (chemical potential means the two material with exhange their inherent energies to be equal)
Explain the basic formula of thermodynamics
dE= TdS- PdV+ mewdN
An infinitesimal chuck of energy
Mew is chemical potential
N is number
So how much energy is associated with a thing and N is how many things you have
Explain
+Q
-Q
+W
-W
Heat in, endothermic, needs heat from surroundings
Heat out, exothermic, released heat to surroundings
Work in, work done on the system
Work out, work done on the surroundings
What is the equation for work
Explain when negative and positive
W = F • x
If the force and x are in opposite directions, work is negative
If the force and x in same directions, work is postive
Force is acting over a distance which causes Work
What is the equation for pressure work
If we had the force but it was not over a distance what does this mean
W= -PdV
For example if we just had pressure but there was no movement in the column (no change in V) there is no work
What are the pressure (expansion) work approximations
Expansion against a vacuum
Constant external pressure
Varying external pressure (isothermal, reversible)
Explain the expansion against a vacuum assumption the pressure work
If you have a vaccum, it has no external pressure
This means there is no force acting on the gas in the vacuum
dW= -P ext dV = 0
Example
if you let a gas freely expand in the vaccum, there is no external pressure on it, no resistance to overcome, it’s not doing work to expand, its energy isn’t changing
Zero work since the force is zero and there is no change in the energy of the gas
Explain the constant external pressure assumption for pressure work
We would use the assumption that the external pressure is constant in every situation
Because your doing a reaction for example isn’t likely to change the pressure around you
W= -Pext (Vf - Vi)
Since only thing changing is the volume
Explain the varying external pressure assumption for pressure work
If the system is completely sealed and nothing could escape, we say that the external pressure is non constant
So now the P is a function of the Volume
Now need to do integral equation since now pressure changes based on the volume changing
Formula on sheet
What are isotherms and adiabats assumptions
Give example
isotherm: constant temp, slow
reaction is slow so there is enough time for heat transfer between the system and surrounding, meaning the temperature doesn’t change due to equilibriating
Adiabatic: no heat exchange, fast
very isolated, the reaction would be so fast that there is no time to exchange the heat to or from the surroundings
To use these assumptions you need to determine if the system is close enough to the assumption (ie. fast or slow)
Explain doing a reaction in a calorimeter and the calorimeter gets cold
In calorimeter, Heat can’t escape
Endothermic reaction
If machine gets cold, that means energy from inside the calorimeter got absorbed to be used in the reaction
Means that energy may have gone into making a bond
Explain heat capacity and the assumptions
If you increase the energy and have small heat capacity what does this mean
If doing a reaction in a calorimeter
Heat capacity (C) = delta energy/ delta temp
Meaning delta E= heat capacity x delta temp
Can assume we either have constant volume or constant pressure
Means you need higher temp (more E, less C, more T)
Whag does it mean for work if you have a constant volume
No work is being done
Since delta W = -P delta V
No change in volume, no change in work
In a calorimeter If you have constant volume what does this mean for heat capacity
There is no work being done (since constant volume)
Since no work, the energy is just coming from heat (Q)
Means that during constant volume, instead of finding energy we are finding heat
So delta Q = Delta E (at constant volume)
What is included in heat capacity
Eqiupartition
What is equipartition
When energy goes into a material , It’s equally broken down into different ways of storing that energy
What are the three equations for
Translational (kinetic)
Rotational
Spring energy
1/2mv^2
1/2 Iw^2
1/2 Kx^2
What forms of energy present in
Solid
Liquid
Gas
Solid:
Al together has vibrational energy: 1/2 mv^2 + 1/2 kx^2
Which takes into account both the fact at some point molecule in the solid can move and move the one next to it, but that if one molecule pushes, the other pushes back like a spring
(at some point in between the pushing and pulling in the lattice, one molecule is moving, giving the translation part)
So both translation and spring to make vibrational energy
Not rotational (because of try to spin in the lattice, the structure will break, no more solid)
Liquid:
Kinetic
Spring
Rotational
Gas:
Kinetic
Rotational
spring, multiple of them don’t have intermolecular interactions to do the push and pull between each other, one single atom can vibrate though
What does the fact that solids have the vibrational energy as:
1/2 mv^2 + 1/2 kx^2
Tell us about equipartion
1/2 mv^2 + 1/2 kx^2
Can be split into x y and z directions because the forces can happen in each direction
So vx vy vz,
kx , ky, kz
In equipartition, for every squared degree of freedom, you can store energy of 1/2kbT
So 1/2 mv^2 + 1/2 kx^2
Turns to
1/2kbT + 1/2kbT = kbT (x direction)
Since In x y and z direction
E = 3 kbT
Or Cv = 1/2 (R) so Cv=3R
For a 3D solid
Explain how E=3 kbT aA d Cv = 3R for a solid
Since Cv = 3R describes temperature
Where R is avogadro x Kb
If you multiply Cv by T (since delta E= Cv delta T)
You get E= 3 KbT explains the energy
Heat capacity times temp gives energy
What is energy for a solid in equipartions and heat capacity
E = 3 KbT
Cv = 3R
Kb is basically R
Slode 22 taking about energy levels also some slides in next lecture
Idk
