| Robert Boyle,Anglo-Irish |
- first reliable measurement on properties of gases (1662)
- Boyle’s Law (Pressure – Volume Relationship)
- at constant temperature, the pressure of a fixed amount (i.e., number of moles n) of gas varies inversely with its volume.
- P1V1=P2V2= constant
- Gases are highly compressible because when a given mass of a gas is compressed, the same number of molecules occupy a smaller space
- This means that gases become denser at high pressure.
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| Charles’ Law |
- Temperature – Volume Relationship
- At constant pressure, volume of a gas increases on increasing temperature and decreases on cooling. (V = k2T )
- This new temperature scale is called the Kelvin temperature scale or Absolute temperature scale.
- Kelvin scale of temperature is also called Thermodynamic scale of temperature and is used in all scientific works.
- Each line of the volume vs temperature graph is called isobar.
- The lowest imaginary temperature at which gases are supposed to occupy zero volume is called Absolute zero.
- All gases obey Charles’ law at very low pressures and high temperatures
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| Gay Lussac’s Law |
- Pressure- Temperature Relationship
- Pressure in well inflated tyres of automobiles is almost constant, but on a hot summer day this increases considerably and tyre may burst if pressure is not adjusted properly.
- During winters, on a cold morning one may find the pressure in the tyres of a vehicle decreased considerably.
- At constant volume, pressure of a fixed amount of a gas varies directly with the temperature. Mathematically. P/T = constant.
- This relationship can be derived from Boyle’s law and Charles’ Law.
- Pressure vs temperature (Kelvin) graph Each line of this graph is called isochore.
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| Avogadro Law,Italy, 1811 | Volume – Amount RelationshipEqual volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules.As long as the temperature and pressure remain constant, the volume depends upon number of molecules of the gas V=k4n. |
| STP |
- Standard temperature and pressure means 273.15 K (0°C) temperature and 1 bar (i.e., exactly 105 pascal) pressure.
- These values approximate freezing temperature of water and atmospheric pressure at sea level.
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| Dalton Partial pressure, 1801 |
- Total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases
- In a mixture of gases, the pressure exerted by the individual gas is called partial pressure.
- pTotal = p1 +p2 +p3 +…..
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| gas liquification |
- At 30.98 C carbon dioxide remains gas upto 73 atmospheric pressure. At 73 atmospheric pressure, liquid carbon dioxide appears. Therefore, 30.98 C is called critical temperature of carbon dioxide. Because this is the highest temperature at which liquid carbon dioxide is observed.
- A gas below the critical temperature can be liquefied by applying pressure, and is called vapour of the substance.
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