Statement Number Assessment Statement 1021 Deduce an expression for the work involved in a volume change of a gas at constant pressure 1022 State the first law of thermodynamics 1023 Identify the first law of thermodynamics as a statement of the principle of energy conservation ID: 783193
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Slide1
Thermodynamics
Topic 10
Sections 2 and 3
Slide2Statement Number
Assessment Statement
10.2.1Deduce an expression for the work involved in a volume change of a gas at constant pressure10.2.2State the first law of thermodynamics10.2.3Identify the first law of thermodynamics as a statement of the principle of energy conservation10.2.4Describe the isochoric (isovolumetric), isobaric, isothermal and adiabatic changes of state of an ideal gas10.2.5Draw and annotate thermodynamic processes and cycles on P-V diagrams10.2.6Calculate from a P-V diagram the work done in a thermodynamic cycle10.2.7Solve problems involving state changes of a gas
10.2 Processes
(The First law of Thermodynamics
)
Slide3By definition: The study of the conditions under which thermal energy can be transferred through performing mechanical work
Macroscopic Properties: Pressure, Volume and Temperature—all used to determine the amount of work that is/can be done by or to a sample of gas.
Thermodynamics
Slide4Internal Energy:
The sum of the total kinetic energy of the molecules in a sample of a gas and the potential energy associated with the intermolecular forces with that gas.
Ideal Gases: assume that the intermolecular forces are non-existent, so potential energy = 0Therefore the internal energy is solely related to the kinetic energy (which is random…each molecule is likely different)Average Kinetic Energy: Internal Energy
Slide5Internal energy of a fixed quantity of a gas (constant number of moles) will only depend on the
temperature
. It does NOT depend on volume or pressureFree-Expansion: when a gas is allowed to expand in a way that is not constricted—both the volume an pressure change in such a way that the temperature will remain constant (in an ideal gas)Thus—the internal energy is constant for a given temperature of ideal gas.Internal Energy
Slide6The complete set of objects being considered in a particular scenario/problem
Open System
Mass is free to enter and/or leave the systemClosed SystemMass is not free to enter and/or leave the system. The quantity of the gas will remain constantIsolated SystemNo energy in any form can enter or leave the systemSystems
Slide7The
State
of a system is known when particular quantifiable characteristics of the system are known, such as the following:PressureVolumeTemperatureInternal EnergyState Function: a characteristic of the system.If two gases, originally in different (thermodynamic) states, are brought to the same state, the gases will have the same internal energy—no matter how they got there.State of a System
Slide8Thermal Energy and
Work
Doing work, or adding or removing thermal energyRelated to a CHANGE in the state, not in the state itselfA gas does not “contain” thermal energy—it can transfer it when it changes stateA gas does not “contain” work—it has work done to it when compressed, or work done by it when expandedNon-state functions
Slide9Work Done by/to a Gas
Imagine a Piston—cross sectional area
AChange the position of the piston by applying a force to expand or compress the gas Volume changesW = P·ΔV
Slide10PV diagrams
Slide11PV Diagrams
Total work done by the gas as it expands (or to the gas as it’s compressed) = area under the curve
Closed loop? Total (net) work done to/by the system = enclosed area
Slide12Those processes in which the
pressure
of the system remains constant while the volume and temperature changeResults in a horizontal line on a PV diagram (Isobar)Isobaric Processes
Slide13Those processes in which the volume remains constant while the pressure and temperature change
Results in a vertical line on the PV diagram (an
Isochore)No work is done during an isochoric processIsochoric Processes
Slide14Those processes in which the temperature remains constant (and, as a result, the internal energy)
The pressure and volume will each change
Isothermal Process
Slide15Thermodynamic Processes are any processes that will result in the change of the state of a system
Heating a gas
Compressing the gas (doing work TO the gas)Expansion of the gas (work done BY the gas)