1. 1 st Law of Thermodynamics * Equation 2. Gases and Work *Equation 3. Efficiency *Equation 4. Entropy 5. 2 nd Law of Thermodynamics 6. Heat Death.

1. 1st Law of Thermodynamics *Equation

2. Gases and Work *Equation

3. Efficiency *Equation

4. Entropy5. 2nd Law of

Thermodynamics6. Heat Death

The change in the total internal energy (thermal energy) of a system is the sum of the work done on it or by it, and the quantity of heat that has been added to or removed from the system

∆U = Q + W∆U =

change in Total

Internal Energy

Q = net heat transferred (“gained”

or “lost”)

W = net work done on or by

the system

Heat (Q)Heat (Q)◦Removed from the system, Q is

negative

◦Added to the system, Q is positive

Work (W)Work (W)◦Done by the system, W is negative

◦Done on the system, W is positive

A beaker sitting on a hot plate receives 100 J A beaker sitting on a hot plate receives 100 J of heat (and does no work). By how much of heat (and does no work). By how much does the internal energy of the water does the internal energy of the water increase?increase?

If 10 J of energy is added to a system that If 10 J of energy is added to a system that does 4 J of external work, by how much will does 4 J of external work, by how much will the internal energy of that system be the internal energy of that system be raised?raised?

∆U = Q + W ∆U = (+100) + 0 = +100 J

∆U = Q + W ∆U = (+10) + (- 4 ) = + 6 J

500 Joules of work are done 500 Joules of work are done onon a system. In a system. In the process a small amount of heat, 25 J, is the process a small amount of heat, 25 J, is dissipated from the system. What is the dissipated from the system. What is the change in the total internal energy of the change in the total internal energy of the system?system?

∆U = Q + W ∆U = (-25) + (+500) = + 475 J

A system initially contains 27 J A system initially contains 27 J of internal energy. Heat is then of internal energy. Heat is then added to the system. If the added to the system. If the final internal energy is 34 J and final internal energy is 34 J and the system does 26 J of work, the system does 26 J of work, how much heat was added to how much heat was added to the system?the system?

∆U = Q + W ∆U = (+100) + 0 = +100 J

A 200 g quantity of water is A 200 g quantity of water is heated in a beaker and then is heated in a beaker and then is poured onto a thermos. The poured onto a thermos. The system’s internal energy system’s internal energy increases by 8.3x103 J of energy increases by 8.3x103 J of energy is transferred to the surrounding is transferred to the surrounding air. How much work is done on air. How much work is done on the thermos?the thermos?

Internal energy in a system can converted to mechanical energy (as well as other energy storage modes) to do work.HOW??Particles in warmer bodies move faster than particles in cooler bodies

◦higher temperature means more active particles (known as the

)Because of this, heating of a sealed Because of this, heating of a sealed pistol containing a gas will result in:pistol containing a gas will result in:particles moving fasterparticles moving fastervolume of the gas increasesvolume of the gas increasespressure inside the sealed container pressure inside the sealed container increasesincreases

When the volumevolume of a gas decreasesdecreases, it is because work has been done on the gas by the surrounding system (-W)(-W)◦Gas is Gas is

compressedcompressed◦Pressure Pressure

increasesincreasesWhen the volumevolume of a gas increasesincreases, the gas can do work on the surrounding system (+W)(+W)◦Gas expandsGas expands◦Pressure Pressure

decreasesdecreases

The air/gas inside the cylinder is compressed. Once ignited, it expands

rapidly to power the engine (does work).

W = P •ΔVW = net

work done on or by the gas

P = pressure inside of a closed system

“change in volume”

ΔV = Vf - Vi

The carbon dioxide in a fire extinguisher is at room temperature. But when the carbon dioxide is expelled through the nozzle, it can get cold enough to chill the water vapor in the air to snow.

How is this possible?How is this possible?

◦It is impossible to convert all internal energy into purely mechanical energy & work

◦Some heatheat (Q)(Q) is ALWAYS “lost” to the system, so as long as a machine has moving parts, it will never be 100% efficient.

% Efficiency = (Workout / Workin) x 100

A Rube Goldberg design…A Rube Goldberg design…In reality, this could never work!

• Entropy is a measure of disorderEntropy is a measure of disorder

One of the ideas involved in the concept One of the ideas involved in the concept of entropy is that nature tends from of entropy is that nature tends from

order to disorder in isolated systems. order to disorder in isolated systems. This tells us that the left hand box of This tells us that the left hand box of

molecules happened before the right. molecules happened before the right. 

You can observe that nature, from the largest system to the You can observe that nature, from the largest system to the smallest, tends to take things from order to disorder. It is a smallest, tends to take things from order to disorder. It is a part of our common experience. Spend hours cleaning your part of our common experience. Spend hours cleaning your desk, your basement, your attic, and it seems to desk, your basement, your attic, and it seems to spontaneously revert back to disorder and chaos before your spontaneously revert back to disorder and chaos before your eyes. eyes.

Most Probable = Least UsefulMost Probable = Least Useful Thermal energy Thermal energy at equilibrium is an example of ”at equilibrium is an example of ”less usefulless useful” ”

energy since the molecules are energy since the molecules are uniformly distributed in a uniformly distributed in a high entropy state.high entropy state.

If hot water is forcibly separated from cold water, heat will If hot water is forcibly separated from cold water, heat will flow & ‘useful’ work can be done.flow & ‘useful’ work can be done.

Natural and spontaneous processes will Natural and spontaneous processes will always move towards a state of greater always move towards a state of greater ENTROPYENTROPY (disorder)(disorder)

In order to prevent (or decrease) entropy, you must

inputinput energy into the system

• Staying ordered is difficultStaying ordered is difficult– Easy to disorder the tower Easy to disorder the tower

(knock it down)(knock it down)• Environment is full of random Environment is full of random

things that can destroy the things that can destroy the order of the towerorder of the tower

• Work and/or Energy are Work and/or Energy are necessary to keep the tower necessary to keep the tower from breaking downfrom breaking down– Systems need energy just Systems need energy just

to stay the sameto stay the same– Even more energy input is Even more energy input is

needed to build systemsneeded to build systems

The Heat Death of the universe refers to a time in the distant future when the whole universe:

a)Runs out of energy.b)Overheatsc)Freezesd)None of the above.

Many scientists believe that the ultimate fate of the universe is a “heat death” in which the whole

universe is at one uniform temp. This would represent maximum entropy. No life could exist,

since life requires energy uptake and expenditure.

The Heat Death refers to a time when the whole universe comes to the same temperature. It might be hot, or it might be cold, or it might be just right. It doesn’t matter what it is just as long as it is the same all over. The universe is not separated into hot and cold places. The starts are hot; the space between the stars is cold, but each day the stars get a little cooler as they radiate their energy—and each day the place the energy goes to gets warmer. Sooner or later the temperature difference must vanish.

After heat death the universe will still have energy, but the energy will be all the same temperature, which takes away it’s ability to do work. It has the potential to do work only if a cooler place can be found.