Presentation on theme: "Add a slide just before efficiency that explains why Qlow exhaust is necessary."— Presentation transcript:
Add a slide just before efficiency that explains why Qlow exhaust is necessary
Ch15 Thermodynamics Zeroth Law of Thermodynamics If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. First Law of Thermodynamics The Internal Energy of a closed system will be equal to the energy added to the system by heating minus the work done by the system to its surrounding Second Law of Thermodynamics Heat flows out from hot objects to cold; heat does NOT flow from cold to hot
Thermal Energy Thermal Energy: The total internal Energy Internal Energy: The sum of the kinetic and potential energies of the internal motion of particles that make up an object.
Internal Energy The sum of all the energy of all the molecules in an object (thermal energy) Internal Energy of an Ideal Gas Brass
Ch15 Thermodynamics Heat – Transfer of energy due to ΔT Work – Transfer of energy NOT due to ΔT Q – Heat W – Work –W done on the system is negative (Giancoli) –W done by the system is positive (AP WS) ΔU – Change in energy
Ch15 Thermodynamics First Law of Thermodynamics Heat added is + Heat lost is - Work on system is – Work by system is +
Ch15 Thermodynamics The distinction between work done on the gas and work done by the gas is one your equation sheet and book define differently The area under the P-V curve will always be the work done by the gas during the process
First Law of Thermodynamics 2500J of heat is added to a system, and 1800J of work is done on the system. What is the changed in internal energy of the system? (Q) 2500J of heat will increase the Internal Energy (W) 1800J of work done ON the system will … Is the work positive or negative? Why? Did the temperature increase or decrease?
Ch15 Thermodynamics Isothermal process: Constant temperature –The system is in contact with a heat reservoir –Change of phase The work done by the gas in an isothermal process equals the heat added to the gas
Isothermal process: Constant temperature, i.e. PV is constant Which Isothermal process is at a higher Temperature? Which Isothermal process does more work?
Adiabatic Adiabatic Process: No heat in or out of the system –Well insulated (like a thermos) –The process happens very quickly (firing of a car cylinder)
Work Given the following two processes: Isothermal and Adiabatic. Both processes start at 10Pa and end with a volume of 10m 3 During which process is more work done? Estimate the work done in each process.
Isovolumetric Isovolumetric: (Isochoric) No change in volume –Inside a ridged container
Isobaric Isobaric: No change in pressure –Movable piston
Internal Energy ΔU 1 mole of an ideal gas is brought from point a to point c by 3 different process paths. Which path has the highest change in internal energy? 1) 2) 3) 4) All the same 5) Unknown 10 20 30 40 50 60 100 400 300 200 a b c d Pressure (Pa) Volume (m 3 )
Work (W) 1 mole of an ideal gas is brought from point a to point c by 3 different process paths. During which path did the gas do the most work? 1) 2) 3) 4) All the same 5) Unknown 10 20 30 40 50 60 100 400 300 200 a b c d Pressure (Pa) Volume (m 3 )
Heat (Q) 1 mole of an ideal gas is brought from point a to point c by 3 different process paths. During which path was the most heat added? 1) 2) 3) 4) All the same 5) Unknown 10 20 30 40 50 60 100 400 300 200 a b c d Pressure (Pa) Volume (m 3 )
One mole of monatomic ideal gas is enclosed under a frictionless piston. A series of processes occur, and eventually the state of the gas returns to its initial state with a P-V diagram as shown below. Answer the following in terms of P 0, V 0, and R. Find the temperature at each vertex. Find the change in internal energy for each process. Find the work done by the gas for each process.
2 Volume m 3 10 An ideal gas is slowly compress at constant pressure (2.0 ATM) from 10.0L to 2.0L Heat is then added to the gas holding the volume constant and the pressure and temperate are allowed to rise until the temperature reaches its original value. a)Calculate the total work done by the gas b)Calculate the total heat flow into the gas Pressure Pa
In an engine 0.25 moles of an ideal gas in the cylinder expands rapidly against the piston. In this process, the temperature of the gas drops from 1150K to 400K. a)What type of process is this? b) How much work does the gas do? Is the work done by the gas positive or negative?
Efficiency Efficiency (e): the ratio of work W done by the system to the input heat Q H
An automobile engine has an efficiency of 20% and produces an average of 23,000J of mechanical work per second. a) How much input heat is required? b) How much heat is discharged as wasted per second? a) b)
When a gas is taken from a to c along the curved path shown, the work done by the gas is W = -35 J and the heat added to the gas is Q = -62 J. Along path abc, the work done is W = -51J. a) What is Q for path abc? b) If Pc = 1/2 Pb, what is W for path cda? c) What is Q for path cda? d) What is Ua - Uc? e) If Ud - Uc = 4 J, what is Q for path da?
When a gas is taken from a to c along the curved path in shown, the work done by the gas is W = -35 J and the heat added to the gas is Q = -62 J. Along path abc, the work done is W = -51J. a) What is Q for path abc? -78J b) If Pc = 1/2 Pb, what is W for path cda?25.5J c) What is Q for path cda? 52.5J d) What is Ua - Uc? 27J e) If Ud - Uc = 4 J, what is Q for path da? 23J
Is the car’s efficiency higher or lower as the car warms up?