0th Law of ThermodynamicsIf system A is in thermal equilibrium with system B, andsystem B is in thermal equilibrium with system C, thensystem A must be in thermal equilibrium with system C.
1 Law of Thermodynamics stConservation of Energy for Heat!Involves three energies: Work, Heat, Internal Energy Internal energy = heat added to the system + the work done on the system. ∆U = Q + W Sign Conventions: Heat added + Work on system + Heat lost – Work by system –
U, Q, and WU = Internal energy depends on change in temperatureQ = Heat depends on transfer of heat energyW = Work W = F•d = P A d = P ∆V (P = F/A)
4 Different EventsIsobaric Constant PressureWork is done by expanding volume Example: ∆U = Q + W Brick on top of sealed ∆U = Q + P∆V canister. Same force over same area ∴ pressure doesn’t change.
Isochoric (isometric) Constant volumeAll heat changes intointernal energyIf ∆V = 0, then W = 0 ∆U = Q + W ∆U = Q + 0 Examples: Inside Pressure Cooker, ∆U = Q Mist above soda. Volume stays the same. Pressure rapidly decreases. Temperature rapidly decreases causing the gas to be pushed out
Isothermal Constant TemperatureHeat is converted tomechanical workIf ∆T = 0, then ∆U = 0 ∆U = Q + W Example: 0=Q+W Boiling Water Q = –W
Adiabatic (GreekAdiabatos: Impassable) No heat transferSystem is extremely wellinsulated or processhappens so fast that heatdoesn’t have time to flowin or outIf no heat transfer, Q = 0 Example: Stretching rubber band∆U = Q + W quickly – Not enough time∆U = 0 + W for heat transfer, so the∆U = W work done goes into internal energy.
Sample 2The internal energy of the gas in a gasolineengine’s cylinder decreases by 195 J. If 52.0 J ofwork is done by the gas, how much energy istransferred as heat? Is this energy added to orremoved from the gas?∆U = Q + W-195 = Q + -52.0Q = -143 J because it is negative it is removed
2nd Law of ThermodynamicsHigh Temp Engine WorkLow TempHeat Engines any device that changes heat energy to mechanical energy
Entropy (S) measure of the disorder of a systemEntropy of a system tends to increase. (Become moredisordered)Another statement of the 2nd Law Natural processes tend to move toward a state ofgreater entropy.R.J. Clausius (German physicist, 1822-1888)Said 2nd Law deals with the direction a process will goClausius’ Statement of 2nd Law of Thermo. Heat flows from hot cold
Most general form:Natural processes tend to have a preferred direction in which they tend to move. ie. An apple doesn’t jump up to a tree, hot water does not get cold over a fire, etc.3rd Law of ThermodynamicsIt is impossible to reach Absolute Zero.