chem 6&10

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  1. exothermic
    energy flows out of the system. In any exothermic reaction, some of the potential energy stored in the chemical bonds is being converted to thermal energy via heat.
  2. endothermic
    heat flow into a system
  3. enthalpy H
    • H= E + PV
    • change in H = change in E + change in PV
  4. when calculating change in enthalpy for neutralization reaction, energy released by the reaction=
    • energy absorbed by the solution=
    • specific heat x mass of solution x increase in temperature =
    • s x m x delta T
  5. Hess's law
    the change in enthalpy is going from a given set of reactants to a given set of products is the same whether the process takes place in one step or a series of steps
  6. energy
    • the capacity to do work or produce heat
    • is conserved (first law of thermodynamics)
    • can be converted from one form to another
    • is a state function
    • potential energy: store energy
    • kinetic energy: energy due to motion
    • The internal energy for a system is the sum of its potential and kinetic energies
    • The internal energy of a system can be changed by work and heat: E= q + w
  7. work
    • force applied over a distance
    • for an expanding/ contracting gas
    • not a state function
    • w= -P delta V
  8. Dipole- dipole forces
    • attractions among molecules with dipole moments
    • are forces that act between polar molecules
    • d-d forces are only about 1% stronger than covalent or ionic bonds
    • hydrogen bonding is a particular strong form of d-d attraction
  9. h-bond
    • occurs in molecules containing h bonded to a highly electronegative element: F, O, N
    • produces usually high boiling points
    • eg: methanol CH3OH
    • ethanol CH3CH2OH
  10. London dispersion forces
    • forces that exist among noble gas atoms and nonpolar molecules
    • instantaneous dipole that occur accidentally, relatively weak and short-lived
    • eg: H2, CH4, CCl4, and CO2
  11. unit cell
    the smallest repeating unit of the lattice
  12. intermolecular force
    occur between, rather than within the molecules. weaker
  13. Liquid state
    low compressibility, lack of rigidity, high density compared with gases.
  14. surface tension
    • the resistance of a liquid to an increase in its surface area
    • liquids with large intermolecular forces such as polar molecules, tend to have high surface tensions.
  15. capillary action
    • the spontaneous rising of a liquid in a narrow tube.
    • cohesive forces: the i.f. among the molecules of the liquid
    • adhesive forces: the forces between the liquid molecules and the container
  16. Bragg equation
    n入 = 2d sin theta

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chem 6&10
2009-11-28 11:14:04

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