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Asignatura: Química bàsica I, Profesor: Raimon Gargallo, Carrera: Química, Universidad: UB
Tipo: Apuntes
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¡No te pierdas las partes importantes!
Un químico:
Microscòpia d’efecte túnel http://www.aip.org/png/html/corral.htm
http://chemistry.tutorvista.com/physical- chemistry/intermolecular-forces.html
Intramolecular
http://www.kentchemistry.com/links/bonding/Hbonding.htm
When were these gases discovered?
Pressure is caused by collisions between gas molecules and a surface
Collisions exert an almost constant force on the surface
Therefore, P = Force done by a gas / Area
What is the effect of the number of molecules, speed and area, on pressure?
“For a fixed amount of an ideal gas kept at a fixed temperature, P [pressure] and V [volume] are inversely proportional”
fewer collisions lower pressure
more collisions higher pressure
“At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature on the absolute temperature scale”
Absolute T is temperature in K
slope of line = k
x-intercept: T when V = 0 absolute zero (William Thomson)
Cl 2 H 2
O 2
“Two given samples of an ideal gas, at the same temperature, pressure and volume, contain the same number of molecules” (1811, but not accepted until the Karlsruhe congress in 1860)
at 273.2K and 1atm (standard temperature and pressure conditions)
In other words:
Pressure decreases (1 bar < 1 atm), so volume increases.
Temperature increases, so volume increases.
In chemistry, standard condition for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data.
There are many different standard conditions!
According to Atkins’s nomenclature:
At low P, a mixture of gases (which do not react among them) behaves as a pure gas
Atmospheric air (a mixture) at low pressure can be regarded as a pure gas
Dalton’s law of partial pressures: total pressure is equal to the sum of individual pressures of gases in a mixture
How will affect the (hypothetical) interaction among molecules to the total pressure?
Molar fraction of gas A in a mixture (χA): moles of gas A divided by the total number of moles
χA= nA / (nA + nB +…)
χA+ χB+ … = 1
If χA= 1 pure gas
PA = χA· P
