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Topic 9: Thermodynamics. Notes. This work by PMT Education is licensed under CC BY-NC-ND 4.0. 9 - Thermodynamics. 9.144 - Thermal energy transfer. You can measure the amount of energy required to change the temperature of a substance using the following formula: Δ E = m cΔθ. Where ΔE is energy required, m is the mass, c is the specific heat ...
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- What is true of Isothermal Process. (a) ΔT >0. (b) ΔU=0. (c) ΔQ=ΔW. (d) PV=constants. Solution. In an Isothermal Process. Temperature remains constant ΔT =0.
- Two absolute scales A and B have triple points of water defined as 200A and 350A. what is the relation between Tand T. Solution-2. Given that on absolute scale.
- A gas is contained in a cylinder with a moveable piston on which a heavy block is placed. Suppose the region outside the chamber is evacuated and the total mass of the block and the movable piston is 102 kg.
- At 27°C,two moles of an ideal monatomic gas occupy a volume V.The gas is adiabatically expanded to a volume 2V. (a)Calculate the ratio of final pressure to the initial pressure.
- 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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Typical examination questions (with answer notes) The following questions are adapted from previous class/degree examinations in this topic, comprising a mixture of long (15 mark) and shorter (5 mark) examples. Answer notes do not necessarily comprise the full solution, and are provided for your guidance only. You are strongly advised to ...
9.12: Entropy and the Second Law of Thermodynamics- Disorder and the Unavailability of Energy; 9.13: Statistical Interpretation of Entropy and the Second Law of Thermodynamics- The Underlying Explanation; Problems & Exercises. 9.1: Temperature; 9.2: The Ideal Gas Law; 9.10: Carnot’s Perfect Heat Engine- The Second Law of Thermodynamics Restated
Answer is (C). 7. Steam enters a turbine with a velocity of 40 m/s and an enthalpy of 3433.8 kJ/kg. At the outlet, 2 meters lower than the inlet, the velocity is 162 m/s, and the enthalpy is 2675.5 kJ/kg. A heat loss of 1 kJ/kg is experienced from the turbine casing. The work output per unit mass is closest to. 650 kJ/kg.
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First law of thermodynamics. When energy passes, as work, as heat, or with matter, into or out from a system, the system's internal energy changes in accord with the law of conservation of energy. This means that perpetual motion machines (of the first kind) are impossible. ΔU system = Q - W. where . Q = heat. W = work done on the system
