Thermo 2 Energy

Question 1

What are the forms of energy

Answer 1

Heat

Kinetic

Gravitational

Electrical

Chemical

Question 2

Explain the story of energy

Answer 2

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

Question 3

Explain the energy conservation equation and what it tells us

Answer 3

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

Question 4

What is Q

What is W

Answer 4

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

Question 5

What are the three types of systems

What do they mean

Answer 5

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

Question 6

Explain the equilibrium conditions

Answer 6

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)

Question 7

Explain the basic formula of thermodynamics

Answer 7

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

Question 8

Explain

+Q
-Q
+W
-W

Answer 8

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

Question 9

What is the equation for work

Explain when negative and positive

Answer 9

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

Question 10

What is the equation for pressure work

If we had the force but it was not over a distance what does this mean

Answer 10

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

Question 11

What are the pressure (expansion) work approximations

Answer 11

Expansion against a vacuum

Constant external pressure

Varying external pressure (isothermal, reversible)

Question 12

Explain the expansion against a vacuum assumption the pressure work

Answer 12

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

Question 13

Explain the constant external pressure assumption for pressure work

Answer 13

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

Question 14

Explain the varying external pressure assumption for pressure work

Answer 14

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

Question 15

What are isotherms and adiabats assumptions

Give example

Answer 15

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)

Question 16

Explain doing a reaction in a calorimeter and the calorimeter gets cold

Answer 16

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

Question 17

Explain heat capacity and the assumptions

If you increase the energy and have small heat capacity what does this mean

Answer 17

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)

Question 18

Whag does it mean for work if you have a constant volume

Answer 18

No work is being done

Since delta W = -P delta V

No change in volume, no change in work

Question 19

In a calorimeter If you have constant volume what does this mean for heat capacity

Answer 19

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)

Question 20

What is included in heat capacity

Answer 20

Eqiupartition

Question 21

What is equipartition

Answer 21

When energy goes into a material , It’s equally broken down into different ways of storing that energy

Question 22

What are the three equations for
Translational (kinetic)
Rotational
Spring energy

Answer 22

1/2mv^2

1/2 Iw^2

1/2 Kx^2

Question 23

What forms of energy present in

Solid

Liquid

Gas

Answer 23

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

Question 24

What does the fact that solids have the vibrational energy as:

1/2 mv^2 + 1/2 kx^2

Tell us about equipartion

Answer 24

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

Question 25

Explain how E=3 kbT aA d Cv = 3R for a solid

Answer 25

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

Question 26

What is energy for a solid in equipartions and heat capacity

Answer 26

E = 3 KbT

Cv = 3R

Kb is basically R

Question 27

Slode 22 taking about energy levels also some slides in next lecture

Answer 27

Idk