# Ideal gas Assumptions 1.Particles that form the gas have no volume and consist of single atoms. 2.Intermolecular interactions are vanishingly small.

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Ideal gas Assumptions 1.Particles that form the gas have no volume and consist of single atoms. 2.Intermolecular interactions are vanishingly small.

Ideal gas Equations of state PV=NkT P= pressure V= volume N=number of particles of gas k= Boltzmann Constant= 1.38x10 -23 J/K K=Kelvin temperature

Ideal gas Equations of state PV=nRT P= pressure V= volume n=number of moles of gas R= Universal Gas Constant= K=Kelvin temperature

Ideal gas Relationship between Avogadro’s number, Universal Gas constant, and Boltzmann constant.

Kinetic –molecular theory 1.Many molecules are in a container and they behave like point particles.(No volume) 2.The molecules move around randomly, and obey Newton’s laws. 3.The only interactions that the molecules undergo are elastic collisions with each other and the walls of the container.

Kinetic –molecular theory Pressure is a result of the molecules colliding with the walls of the container. As the number of molecules or thir average speed increases, the pressure increases.

Kinetic –molecular theory Results of kinetic-molecular theory.

Kinetic –molecular theory Results of kinetic-molecular theory.

Kinetic –molecular theory Internal energy of an ideal monatomic gas..

Kinetic –molecular theory Other gas laws – the amount of gas does not change

Laws of Thermodynamics The first Law of Termodynamics – If U is the internal energy of a system, than  U=Q-W. If Q>0 System gains heat If Q<0 System loses heat If W>0 Work is done by the system If W<0 Work is done on the system

Laws of Thermodynamics The first Law of Thermodynamics – If U is the internal energy of a system, than  U=Q-W

Table 18-1 Signs of Q and W Q positiveSystem gains heat Q negativeSystem loses heat W positiveWork done by system W negativeWork done on system

Figure 18-1 The Internal Energy of a System

Figure 18-2 Work and Internal Energy

Laws of Thermodynamics At constant pressure, the work done by or on a system is W=PΔV The area under a PV curve represents work. If a process occurs at a constant volume, the work done during the process is 0.

Figure 18-5 A Constant-Pressure Process

Example 18-2 Work Area

Laws of Thermodynamics Isothermal processes – these are processes that take place at a constant temperature. PV=constant

Figure 18-8 Isotherms on a PV Plot

Laws of Thermodynamics Adiabatic processes – these are processes that take place without heat entering or leaving the system.

Figure 18-9 An Isothermal Expansion

Conceptual Checkpoint 18-2 Page 578 Which is the adiabatic curve?

Figure 18-14 A Comparison Between Isotherms and Adiabats

Laws of Thermodynamics A heat engine is a device that converts heat into work. It operates between at least two temperatures referred to as the hot reservoir and the cold reservoir. A classic example is a steam engine.

Example 18-6 Heat into Work

Laws of Thermodynamics Steam engine

Laws of Thermodynamics Sadi Carnot (1796-1832) developed a theorem that allows on to calculate the theoretical efficiency of a heat engine operating between two temperatures. He assumed that in an ideal engine all processes are reversible. If this were true, the engine would have maximum efficiency, and all ideal engines operating between those two temperatures would have the same efficiency.

Laws of Thermodynamics Maximum efficiency of a heat engine.

Laws of Thermodynamics This expression applies to ideal (Carnot) engines. The efficiency of a real engine will always be less. Under what conditions would a ideal engine have an efficiency of 1?

Active Example 18-2 Find the Temperature

Active Example 18-3 Find the Work

Laws of Thermodynamics Recollect – when two objects are in thermal contact heat can flow between them. The second law of thermodynamics. When two objects at different temperatures are brought into thermal contact, the spontaneous flow of heat is always from the high temperature object to the low temperature object.

Laws of Thermodynamics Entropy S is a thermodynamic quantity whose change defined as the heat transferred during a reversible process divided by the Kelvin temperature

Laws of Thermodynamics During an irreversible process the entropy of the universe is increased. During an ideal reversible process the entropy of the universe remains unchanged.

Laws of Thermodynamics Example: 0.125kg of ice melts at 0 o C. The heat absorbed during the process is 4.19x10 4 J. What is the entropy change for the process?

Example 18-9 Entropy Is Not Conserved! Calculate the entropy change for the process.

Laws of Thermodynamics For an irreversible process, entropy will always increase. Unlike energy, entropy is not conserved.

Laws of Thermodynamics Third Law of Thermodynamics It is impossible to lower the temperature of an object to absolute zero in a finite number of steps.

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