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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.
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endothermic
heat flow into a system
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enthalpy H
- H= E + PV
- change in H = change in E + change in PV
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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
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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
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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
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work
- force applied over a distance
- for an expanding/ contracting gas
- not a state function
- w= -P delta V
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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
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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
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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
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unit cell
the smallest repeating unit of the lattice
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intermolecular force
occur between, rather than within the molecules. weaker
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Liquid state
low compressibility, lack of rigidity, high density compared with gases.
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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.
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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
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Bragg equation
n入 = 2d sin theta
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