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2. The zeroth law of Thermodynamics 2.1 Thermodynamical systems Before we embark on deriving the laws of thermodynamics, it is necessary to define the main vocabulary we will be using throughout these lectures. Definition 2.1.1 — ‘Thermodynamical system’ (or ‘system’). Whatever “macroscopic” part of the Universe we select for study.
into doing work. This statement of energy conservation is the first law of thermodynamics, which is defined more formally below. Related End-of-Chapter Exercises: 1 and 13. The first law of thermodynamics is a statement of energy conservation as it relates to a thermodynamic system. Heat, which is energy transferred into or out of a system, can be
- Last time: The First Law of Thermodynamics
- = Q - W
- C ~ α Substances with more internal
- ACT 1
- ACT 1: Solution
- Work Done by a Gas
- V V V
- Constant-Pressure Heat Capacity of an Ideal Gas
- U = -W by.
- Four Thermodynamic Processes of Particular Interest to Us
- f dV
- Example: Escape Velocity
- Next Week
Energy is conserved !!! change in total internal energy heat added to system work done on the system alternatively:
by Note: For the rest of the course, unless explicitly stated, we will ignore KE CM, and only consider internal energy that does not contribute to the motion of the system as a whole.
V degrees of freedom require more energy to produce the same temperature increase: Why? Because some of the energy has to go into “heating up” those other degrees of freedom! The energy is “partitioned equally” “equipartition”
Consider the two systems shown to the right. In Case I, the gas is heated at constant volume; in Case II, the gas is heated at constant pressure. Compare Q , the amount of heat needed to
Consider the two systems shown to the right. In Case I, the gas is heated at constant volume; in Case II, the gas is heated at constant pressure. Compare Q , the amount of heat needed to
When a Consider a cylinder filled with gas. For a small displacement gas expands, it does work on its environment. A dx, the work done by the gas is dW by = F dx = pA dx = p (Adx)= p dV
The amount of work performed while going from one state to another is not unique! It depends on the path taken, i.e., at what stages heat is added or removed. That’s why W is called a process variable. because T varies differently along the paths. (Heat is added at different times.)
Add heat to an ideal gas at constant pressure, allowing it to expand. We saw in the Act that more heat is required than in the constant volume case, because some of the energy goes into work: work W by
α Nk U = − T = − W by p = V − NkT V V T α = − V dT dV → α ∫ = − ∫ T V α ln ( T ) = − ln ( V ) + constant ln ( T α ) + ln ( V ) = ln ( T α V ) = constant V α T = constant Using pV = NkT, we can also write this in the form: pV γ = constant Note that pV is not constant. The temperature is changing.
Isochoric (constant volume) Isobaric (constant pressure)
Isothermal process - ideal gas. FLT Definition of work then use ideal gas law Integral of dV/V Note that the heat added is negative - heat actually must be removed from the system during the compression to keep the temperature constant.
How much kinetic energy must a nitrogen molecule have in order to escape from the Earth’s gravity, starting at the surface? Ignore collisions with other air molecules. How about a helium atom? At what temperatures will the average molecule of each kind have enough energy to escape?
Heat capacity of solids & liquids Thermal conductivity Irreversibility
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2. The zeroth law of Thermodynamics 2.1 Thermodynamical systems Before we embark on deriving the laws of thermodynamics, it is necessary to define the main vocabulary we will be using throughout these lectures. Definition 2.1.1 — ‘Thermodynamical system’ (or ‘system’). Whatever “macroscopic” part of the Universe we select for study.
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1 Introduction. Thermodynamics is the study of heat and temperature. One thing that makes thermodynamics hard (and generally unpopular) is all the damn variables. Everything is related and it's often tough to keep straight what is an independent and what is a dependent variable.
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0) (Hook′s law for rubber). (I.9) The ideal gas temperature scale: As the above example indicates, the zeroth law merely states the presence of isotherms. In order to set up a practical temperature scale at this stage, a reference system is necessary. The ideal gasoccupies an important place in thermodynamics and provides the necessary reference.
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1st law: In an arbitrary TD transformation, let Q = net amount of heat absorbed by the system, and W = net amount of work done on the system. The 1st law states ∆E = Q +W (1) is the same for all transformations leading form a given initial state to a final state (Joule’s law), where E is the total energy (or internal energy, or just
