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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
This is a device that uses work to transfer heat from a low temperature reservoir to a high temperature one. ⌅ Example 5.2 In a household refrigerator, work is done by an electrical compressor which transfers heat from the food storage compartment (cold reservoir) to the kitchen (hot reservoir). ⌅.
- 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
- 273KB
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3. The first law of Thermodynamics With the previous definitions in hand, we are now equipped to tackle the first law of thermodynamics. 3.1 Thermodynamical change Because thermodynamical systems are generally in mechanical and/or thermal contact with their surroundings, nothing really happens until there is a change in external factors.
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the 1st Law of Thermodynamics. Coherent energy Internal energy: random Kinetic and potential motion of small stuff we don’t want to talk about. E = KE + PE + U. int. ΔE = Δ(KE) + Δ(PE) + ΔU. int. Thermal energy Energy of System Entering system (not moving coherently) Work done on system. ΔU = Q. int.
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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Figure 2: The zeroth law of thermodynamics: System A and system B can exchange energy (represented by the two arrows in opposite directions) and are in thermal equilibrium. The zeroth law presents the existence of thermal equilibrium as a transitive property in which if system with system C, then system A is in thermal equilibrium with system.
