Fisica 3r


La sesión de hoy va explicar fenomenos tan interesantes como el que ocurre en el mar en virtud del cual el agua del mar no se sale  o el fundamento de una presa hidraulica.

La presion atmosferica.

Hoy os traigo a clase 4 experimentos que no se podrian explicar si no existiese la columna de aire que repiquetea y golpea toda superficie sobre la faz de la tierra llamada presion atmosferica, que es justamente la fuerza que ejerce cada molecula de aire sobre las superfices , cada choque .

A partir de aqui  mi intencion es explicaros las leyes de los gases, Boyle, charley y Guy-Lussac. Y realizar algunos ejercicios.

os dejo algunos links para que comprobeis las relaciones qaue estas leyes establecen entre las magnitudes Volumen.Presión y Temperatura.

http://www.educaplus.org/gases/ley_gaylussac.html

Versión en Ingles

Traslate to Spanish

Terms

Presure

Armospheric pressure

solid

liquid

gas

particles

barometer

mass

Atmospheric Pressure

This term is the pressure exerted by the air.The air around us, oppor that only we realize this when it moves like wind.

When we put a straw in a glass ,liquit has the same level as the glass. If you sip , air go out and the atmospheric presure makes climb the liquid.

Evangelista Torrecilli Italian physicist and mathematician who invented the barometer..He created a tube approximately one meter long, sealed at the top, filled it with mercury, and set it vertically into a basin of mercury. The column of mercury fell to about 76 cm, leaving a Torricellian vacuum above. As we now know, the column’s height fluctuated with changingatmospheric pressure; this was the first barometer.

The conclusion was the presure makes by the atmophere is like the presure makes a column of mercury. This number is called 1 atmophere then

1 atm= 760 mm Hg=101325 Pa

Gas Laws

Pressure Volume Temperature Relationships

Boyle’s law or the pressure-volume law states that the volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant.

V is proportional to the inverse of P

Another way to describing it is saying that their products are constant.

PV = C

When pressure goes up, volume goes down. When volume goes up, pressure goes down.
From the equation above, this can be derived:

P1V1 = P2V2 = P3V3 etc.

This equation states that the product of the initial volume and pressure is equal to the product of the volume and pressure after a change in one of them under constant temperature. For example, if the initial volume was 500 mL at a pressure of 760 mm Hg, when the volume is compressed to 450 mL, what is the pressure?
Plug in the values:

P1V1 = P2V2

(760 torr)(500 mL) = P2(450 mL)
760 torr x 500 mL/450 mL = P2 844 torr = P2
The pressure is 844 torr after compression.

Charles’ Law:The Temperature-Volume Law

This law states that the volume of a given amount of gas held at constant pressure is directly proportional to the Kelvin temperature.

Vis proportional to T

Same as before, a constant can be put in:

V / T = C

As the volume goes up, the temperature also goes up, and vice-versa.
Also same as before, initial and final volumes and temperatures under constant pressure can be calculated.

V1 / T1 = V2 / T2 = V3 / T3 etc.

Gay-Lussac’s Law:The Pressure Temperature Law

This law states that the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature.

Pis proporitonal to T

Same as before, a constant can be put in:

P / T = C

As the pressure goes up, the temperature also goes up, and vice-versa.
Also same as before, initial and final volumes and temperatures under constant pressure can be calculated.

P1 / T1 = P2 / T2 = P3 / T3 etc.

Avogadro’s Law:The Volume Amount Law

 

Gives the relationship between volume and amount when pressure and temperature are held constant. Remember amount is measured in moles. Also, since volume is one of the variables, that means the container holding the gas is flexible in some way and can expand or contract.

If the amount of gas in a container is increased, the volume increases.If the amount of gas in a container is decreased, the volume decreases.

Vis proportional to n

As before, a constant can be put in:

V / n = C

This means that the volume-amount fraction will always be the same value if the pressure and temperature remain constant.

V1 / n1 = V2 / n2 = V3 / n3 etc.

The Combined Gas Law ( General Law)

Now we can combine everything we have into one proportion:

V is proportional to T divided by P

The volume of a given amount of gas is proportional to the ratio of its Kelvin temperature and its pressure.
Same as before, a constant can be put in:

PV / T = C

As the pressure goes up, the temperature also goes up, and vice-versa.
Also same as before, initial and final volumes and temperatures under constant pressure can be calculated.

P1V1 / T1 = P2V2 / T2 = P3V3 / T3 etc.

The Ideal Gas Law

The previous laws all assume that the gas being measured is an ideal gas, a gas that obeys them all exactly.But over a wide range of temperature, pressure, and volume, real gases deviate slightly from ideal. Since, according to Avogadro, the same volumes of gas contain the same number of moles, chemists could now determine the formulas of gaseous elements and their formula masses.The idea gas law is:

PV = nRT

Where n is the number of moles of the number of moles and R is a constant called the universal gas constant and is equal to approximately 0.0821 L-atm / mole-K.

Links simulators:

http://www.educaplus.org/gases/ley_gaylussac.html

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