KIMIA LINGKUNGAN

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KIMIA LINGKUNGAN

• BAGIAN 2 TERMODINAMIKA

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PREVIEW

• In this third part of the course we     
• define and apply a number of thermodynamic ideas
  and concepts
• become familiar with and apply the 1st and 2nd
  law of thermodynamics
• discuss several thermodynamic processes with the
  aid of pressure-volume (pV) diagrams
• define and discuss the concept of entropy
• apply the laws of thermodynamics to discuss heat
  engines, refrigerators and heat pumps
• introduce parameters to quantify the efficiency
  at which thermodynamic devices operate
• learn about the Carnot cycle and its relation to
  the concept of an 'ideal' engine

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Thermodynamic Systems, States and Processes

• Objectives are to
• define thermodynamics systems and states of
  systems
• explain how processes affect such systems
• apply the above thermodynamic terms and ideas to
  the laws of thermodynamics

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Thermodynamic Systems

• A thermodynamic system is a collection of matter
  which has distinct boundaries.ORA real or
  imaginary portion of universe whish has distinct
  boundaries is called system.ORA thermodynamic
  system is that part of universe which is under
  thermodynamic study.

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1. 1st Law of Thermodynamics

• statement of energy conservation for a
  thermodynamic system
• internal energy U is a state variable
• W, Q process dependent

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Isoprocesses

• apply 1st law of thermodynamics to closed system
  of an ideal gas
• isoprocess is one in which one of the
  thermodynamic (state) variables are kept constant
• use pV diagram to visualise process

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Isobaric Process

• process in which pressure is kept constant

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Isochoric Process

• process in which volume is kept constant

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Isothermal Process

• process in which temperature is held constant

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Adiabatic Process

• process in which no heat transfer takes place

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2. Second Law of Thermodynamics and Entropy

• Objectives are to
• state and explain the second law of
  thermodynamics
• explain the concept of entropy

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2nd Law of Thermodynamics

• states in which direction a process can take
  place
• heat does not flow spontaneously from a cold to a
  hot body
• heat cannot be transformed completely into
  mechanical work
• it is impossible to construct an operational
  perpetual motion machine
• introduces concept of entropy

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Entropy

• property that indicates the direction of a
  process
• entropy is a measure of disorder
• entropy is a measure of a systems ability to do
  useful work
• entropy determines direction of time
• the entropy of an isolated system increases

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2nd Law of Thermodynamics entropy
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2nd Law example
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3. Heat Engines and Heat Pumps

• Objectives are to
• explain what a heat engine is, and compute its
  thermal efficiency
• explain what a heat pump is, and compute its
  coefficient of performance

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Diagram of a Heat Engine
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Heat Engine
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Heat Engine

• A heat engine is a cyclic device that converts
  thermal energy into work output
• It is a device that takes heat from a high-T
  reservoir, converts some of to (useful) work, and
  transfers the rest to the surroundings (a low-T
  reservoir)
• Examples steam engines internal combustion
  engines (car engines)
• Thermal efficiency (what you get out/what you
  put in)
• No heat engine operating in a cycle can convert
  all of its heat input completely to work

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Heat Pump
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Heat Pump

• A heat pump is a (cyclic) device that transfers
  heat energy from a low-T reservoir to a high-T
  reservoir
• Examples air conditioner refrigerator
• Coefficient of performance (what you get
  out/what you put in)
• No heat pump operating in a cycle can transfer
  thermal energy to a low-T reservoir without doing
  some work

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Refrigerator (1)
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Refrigerator (2)
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4. The Second Law Revisited

• it is impossible to produce a cyclic engine that
  generates work by extracting heat from a
  reservoir without expelling some waste heat
• it is impossible to produce a heat pump in which
  the sole result is the transfer of heat from a
  low-T to a high-T body

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5. Third Law of Thermodynamics

• The 3rd law states that
• It is impossible to reach a temperature of
  absolute zero
• It is impossible to have a (Carnot) efficiency
  equal to 100 (this would imply Tc 0).

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Isobaric Expansion Change in Internal Energy

• A quantity of an ideal gas has a volume of 22.4
  litres at STP (standard temperature and
  pressure). While absorbing 315 cal of heat from
  the surroundings, the gas expands isobarically to
  32.4 litres. What is the change in internal
  energy of the gas?
• What is the equilibrium temperature (in degrees
  Celsius) of the gas after expansion?

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Question
Three different experiments are run, in which a
gas expands from point A to point D along the
three paths shown below. Calculate the amount of
work done for paths 1, 2 and 3.
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Questions

• Free Loader Consider the following idea. A ship
  heats its boilers and propels itself without the
  use of coal or oil in the following way. It pumps
  in warm sea water, extracts heat from that sea
  water, concentrates the extracted heat in its
  boilers, and discharges the cooled seawater back
  into the ocean. The discharged water may be ice
  if enough heat has been taken from it. Could this
  idea be made to work?
• Gulf of Mexico Another free loader idea is to
  generate power as follows. Water on top of the
  Gulf of Mexico is quite warm but deep down the
  water is cold. The plan is to heat some gas with
  warm water from the top so it will expand, and
  then cool the gas with water from the bottom so
  it will contract. The gas is alternately expanded
  and contracted so it drives a piston back and
  forth. The moving piston is attached by
  conventional means to an electric generator to
  make electricity. Can this idea be made to work?