First law

Processes

isobaric

isochoric (isovolumetric)

isothermol

adiabatic (isentropic)

Work and Heat in a process

Heat Engines/ Refrigerators

efficiency

Ideal

Second law

entropy

1st Law

Internal energy is the motion of particles.

two things can happen.

Work (positive or negative)

Heat 'flow' (in or out)

Here Q is positive if heat is being added

TO the system

Q is negative if heat is being taken FROM

the system

Also W is positive if it is work done BY the

system on the environment

It is negative if the environment does

work ON it.

S

Processes

There are many ways this internal energy can change. Each doing a different amount of work, and heat flow

Often Ideal gas law helps with this.

We will look at cases where each term is held constant

Main processes

Isobaric

Isochoric

Isothermal

adiabatic

no heat flow

constant temperature

constant pressure

constant volume

Main Processes

It is helpful to do this pictorially on a Pressure Volume graph

Graph

Temperature increase up and right

Area under process is Work done by engine

Increases in volume are positive work

Decreases are negative work

Generally increases in temperature are positive Q,

decreases in temp. are negative Q. (adiabatic is the exception)

Best summed up with a table

This is not all inclusive.

but it is what you 'need' - also use Ideal gas law

example isobaric work:

**An adiabatic process is one where :**

A. Pressure is constant

B. Volume is constant

C. Temperature is constant

D. No heat is exchanged.

A. Pressure is constant

B. Volume is constant

C. Temperature is constant

D. No heat is exchanged.

**In Isochoric processes:**

A. No heat is exchanged

B. The temperature is constant

C. No work is done

D. The pressure is constant

A. No heat is exchanged

B. The temperature is constant

C. No work is done

D. The pressure is constant

Thermodynamics

Linking thermodynamical processes via reversible/nonreversible processes will result in a some work being done for some heat used.

This is the idea of a heat pump, Engine, or Refrigerator.

(TABLE)

Diagram of 1st law

Cyclic - note the 'red' line returns cyclically to the same temperature, so no change in internal energy

Efficiency

We note that the Heat from the higher temperature

is not destroyed but transferred to work and heat low

Solving for efficiency, we want the most going to work

The most efficient cycle is a Carnot engine

It is a set of isothermal and adiabatic steps.

This is because no heat flows in an adiabatic

process, and in isothermal the heat gets

changed to work.

**If 50 J of Heat is**

taken from a hot source

and 20 J of work are produces

what is the efficiency of this

engine

A. 20%

B. 40 %

C. 60 %

D. 250 %

taken from a hot source

and 20 J of work are produces

what is the efficiency of this

engine

A. 20%

B. 40 %

C. 60 %

D. 250 %

**If the temperature range**

that is available for an

engine to perform goes

from 300 - 400 degrees

what is the maximum efficiency

possible

A. 25 %

B. 33 %

C. 75 %

D. 133%

that is available for an

engine to perform goes

from 300 - 400 degrees

what is the maximum efficiency

possible

A. 25 %

B. 33 %

C. 75 %

D. 133%

A Refrigerator is just an engine running backwards.

Instead of taking heat from a High source and changing it to work,

we put work in and take heat from a Low source effectively making it even lower.

Refrigerators also have efficiencies

The text uses a horrible term COP

for coefficient of performance to describe

this efficiency of refrigeration.

Ideally this is:

**2nd law of thermodynamics**

Total entropy of a system plus that of its environment increases as a result of any natural process

corollaries

heat flows from hot to cold spontaneously

any natural process leads to a greater state of disorder

Entropy is calculated by the Heat that flows

over a fixed temperature

This is in practice generally not feasible to use

in an equation, because when heat flows, the

temperature changes.

If looked over little tiny steps, the temperature

would be fixed, while the heat is flowing, and then

you would just add them all up.

In practice this is done by taking the average temperature

**Say I raised the the temperature of 500 g of water from**

22 - 24 degrees Celsius.

the average temperature is 23 or 296

and the heat flow is Q=mcT = 4186

This gives

22 - 24 degrees Celsius.

the average temperature is 23 or 296

and the heat flow is Q=mcT = 4186

This gives

**Entropy is a state variable, yet it can be used to describe microscopic terms to.**

Orderliness

or

probability

Orderliness

or

probability

This then is another version of the 2nd law of

thermodynamics

Because entropy increase, we can say

Natural process tend to move toward a state of greater disorder.

This one might be the most familiar of the different

versions of the 2nd law of thermodynamics

Entropy always increases, disorder always increases, for natural processes.

"I need some clarity on what each law of thermodynamics entails."

"Why are work and heat not state variables?"

"Could you go over the processes of the first law of thermodynamics?"

"Can you go over state variables just a little review?"

"Can you explain the different thermodynamic processes? "

"I have trouble keeping the laws of thermodynamics straight and when to use them. Is there a way to remember when to best apply each one?"

"Can I get a breakdown of the equation to solve for entropy"

"What is an example of a process that is reversible? Irreversible?"