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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.
heat flow into a system
- H= E + PV
- change in H = change in E + change in PV
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
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
- 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
- force applied over a distance
- for an expanding/ contracting gas
- not a state function
- w= -P delta V
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
- occurs in molecules containing h bonded to a highly electronegative element: F, O, N
- produces usually high boiling points
- eg: methanol CH3OH
- ethanol CH3CH2OH
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
the smallest repeating unit of the lattice
occur between, rather than within the molecules. weaker
low compressibility, lack of rigidity, high density compared with gases.
- 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.
- 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
n入 = 2d sin theta
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