chem chapter 6

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alazeidan
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chem chapter 6
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2014-02-05 23:00:33
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  1. Thermodynamics
    is the science of the relationships between heat and other forms of energy
  2. thermochemistry
    the study of the quantity of heat absorbed or evolved by chemical reactions
  3. Energy
    • the potential or capacity to move matter
    • property of matter
    • exists in different forms that can be interconverted 
    • can not be created no destroyed
  4. kinetic energy
    is the energy associated with an object by virtue of its motion
  5. formula for kinetic energy
    Ek=1/2 mv^2

    • ek kinetic energy (joules)
    • m mass in kg
    • v velocity in m/s
  6. calorie (cal)
    non SI unit of energy commonly used by chemists originally defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius
  7. one cal = _______ joules
    4.184
  8. potential energy
    the energy an object has by virtue of its position in a field of force
  9. formula for potential energy
    Ep=mgh

    • Ep - potential energy j
    • m- mass kg
    • g - acceleration due to gravity m/s
    • h - height (m) measured from a standard level -- the surface of the earth
  10. internal energy (U)
    the sum of the kinetic and potential energies of the particles making up a substance
  11. equation for total energy
    Etot= Ep + Ek + U
  12. Law of conservation of energy
    energy may be converted from one form to another but the total quantity of energy remains constant
  13. thermodynamic system
    the substance or mixture of substances under study in which a change occurs
  14. surroundings
    everything in the vicinity of the thermodynamic system
  15. heat
    the energy that flows into or out of a system because of a difference in temperature between the thermodynamic system and its surroundings
  16. thermo-equilibrium
    as long as the system and the surroundings are not insulated from one another energy heat flows between them to establish an equilibrium
  17. heat flows from
    higher temperature region to a lower temperature region
  18. temperature
    proportional to kinetic energy
  19. heat q
    the symbol for heat is denoted by q
  20. q is positive when
    heat is absorbed by the system
  21. q is negative when
    heat is evolved by the system
  22. heat of reaction
    is the value of q required to return a system to the given temperature at the completion of the reaction
  23. exothermic
    is a chemical reaction or a physical change in which heat is evolved and q is negative (reaction vessel warms)
  24. endothermic
    is a chemical reaction or a physical change in which heat is absorbed and q is positive (reaction vessel cools)
  25. enthalpy
    • denoted H is an extensive property of a substance that can be used to obtain the heat absorbed or evolved in a chemical reaction 
    • state function
  26. state function
    a property of a system that depends only on its present state which is determined by variables such as temperature and pressure and is independent of any previous history of the system
  27. change in enthalpy = enthalpy of reaction (delta H)
    • the change in enthalpy for a reaction at a given temperature and pressure 
    • delta H = H(products) - H (reactants)
  28. the enthalpy of reaction equals
    • the heat of reaction at constant pressure
    • deltaH = qp
  29. relationship between enthalpy and internal energy
    H=U+PV

    • H the enthalpy 
    • U internal energy 
    • P pressure
    • V volume
  30. Thermochemical equations
    • the chemical equation for a reaction including phase labels in which the equation is given a molar interpretation and the enthalpy of reaction for these molar amounts is written directly after the equations
  31. rules when manipulating thermochemical equations
    1. when a thermochemical equation is multiplied by any factor the value of delta h for the new equation is obtained by multiplying the value of delta h in the original equation by that same factor

    2. when the chemical equation is reversed the value of delta h is reversed in sign
  32. converting from grams to kilojoules of heat
    (grams of A) X (conversion factor: g A to mol A using molar mass) X (conversion factor mol A to kJ using enthalpy of reaction) -> kilojoules of heat
  33. heat capacity (C)
    the heat required to raise the temperature of a substance one degree Celsius or one kelvin

    q=CdeltaT
  34. specific heat
    the quantity of heat required to raise the temperature of one gram substance by one degree Celsius or kelvin at constant pressure

    q=mCdeltaT
  35. calorimeter
    a device used to measure the heat absorbed or evolved during a physical or chemical change 

    for reactions involving gases a bomb calorimeter is generally used
  36. Hess's law
    for a chemical equation that can be written as the sum of two or more steps the enthalpy change for the overall equation equals the sum of the enthalpy changes for the individual steps
  37. standard state
    • the standard thermodynamic conditions chosen for substances when listing or comparing thermodynamic  data : 
    • 1atm pressure and 25 degrees celcius -- 298 k

    conditions denoted by ()
  38. allotrope
    one of two or more distinct forms of an element in the same physical state
  39. the reference form
    the stablest form of the element under standard thermodynamic conditions
  40. standard enthalpy of formation/standard heat formation
    deltaHf

    is the enthalpy change for the formation of one mole of the substance in its standard state from its elements in their reference form and in their standard states

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