Energy and Chemistry

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Energy and Chemistry

• (Chemical Thermodynamics)

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Energy

• The capacity (on the part of the energy
  possessing entity) to do work or raise the
  temperature of matter
• Force exerted over a distance
• Equivalents
• Pressure exerted through a volume change
• Electrical energy
• Movement of charge between two potential levels

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Quantitation of energy

• MKS system the Joule (J)
• Force mass ? acceleration
• kg ? m s-2
• Distance - meters
• 1 joule 1 kgm2s-2
• CGS system the erg (e)
• 1 erg 1 gcm2s-2
• 1 joule 107 ergs

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Other equivalents

• Electrical energy
• Kilowatt hours
• 1 watt 1 Js-1
• 1 J 2.77778 ? 10-7 kWh

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Non-metric units

• Calorie (cal)
• The quantity of energy needed to raise the
  temperature of
• 1 g of water
• 1 ?C,
• starting from 14.5 ?C
• 1 calorie 4.184 J (A calorie is bigger)
• 1 Calorie (nutritional energy) 1kcal

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Kinetic and Potential

• Kinetic energy - Energy of motion distinct from
  other energies of position or level
• ½ mass ? (velocity)2
• Potential energy energy by virtue of position
  or level (e.g., electric potential)
• Gravitational energy - Gm1m2/r
• Electrostatic energy - ?Q1Q2/r

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Systems

• System and surroundings
• Isolated system
• Closed system
• Open system

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Thermodynamics Laws

• Observed, so far, to be true
• NOT laws in the sense of, say, federal law

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First Law

• Various statements
• Energy can be neither created nor destroyed
• Energy is conserved
• ..

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Thermodynamic State

• The condition of a system as described by a list
  of physical properties such as temperature,
  pressure, volume, electrical potential, etc.

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Thermodynamic State Functions

• Quantity (units of energy usually) which depends
  only on the state of a system
• E, H, G, µ.

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Internal Energy E

• E is the sum of the kinetic and potential energy
  of the system
• Includes EVERY aspect of the system, down to the
  energy of the fundamental components of it
• But we dont know the fundamental components for
  sure!
• Thus we dont know the absolute value of E

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?E

• For two states 1 and 2, each with E, can define
  ?E
• System changes from one state to another Efinal
  Einitial ?E
• Chemical systems Eproducts - Ereactants ?E.

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Heat and work change E

• Heat added to a system (absorbed by a system) q
• Work done on a system (or the negative of the
  work done by a system) w
• ?E q w reflects the first law.

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Enthalpy H

• H E pV
• H q when process occurs (most of chemistry) at
  constant pressure