CHEMISTRY FINALS

The Kinetic Molecular Theory

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* Gas contains minute particles which are so small that the volume they occupy is negligible compared to the volume of the container or the distance between the container
* The gas particles are constantly moving at a rapid random motion such that they collide with each other and against the walls of the container
* The gas particles are considered as hard spheres such that their collisions are perfectly elastic
* This means that no energy is lost during the collision
* The interaction among particles (IMFA), either attractive or repulsive, is negligible
* The average kinetic energy of a gas is directly proportional to its absolute temperature

boyle’s law

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* The gas particles are very small compared to the volume they occupy, thus they are compressible
* The average KE depends only on the absolute temperature of the gas
* Compressing the gas without changing the temperature will not affect its kinetic energy
* Thus, the velocity of the particles will not change, but the frequency of collision with the walls of the container will increase since there is less space for the particles to move about
* This results in an increase in the pressure of the gas
* The law states that the volume of a gas is inversely proportional to its pressure at a constant temperature
* PV = constant
* P1V1 = P2V2
* Practical application – The pop-up button lid of bottled goods indicates the freshness of the unopened bottle

gay-lussac’s law

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* all gases expand equally over a temperature range
* This observation led to his gas law, which states that the pressure of a fixed amount of gas is directly proportional to its absolute temperature at a constant volume
* The law states that the pressure is directly proportional to the Kelvin temperature at constant volume
* Equation
* PT = constant, where T is expressed in Kelvin
* P1T1 = P2T2

charles’s law

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* If the volume of gas is variable, the force of the particle collisions will cause the gas to expand until the pressure returns to its initial value
* The law states that at constant pressure, the volume of the gas is directly proportional to its temperature
* Equation
* VT = constant, where T is expressed in Kelvin
* V1T1 = V2T2

avogadro’s law

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* The volume of a gas is directly proportional to the number of particles at the same pressure and absolute temperature
* The law states that the volume of a gas is directly proportional to the number of particles at the same pressure and absolute temperature, regardless of the nature of the gas
* Equation
* V1n1 = V2n2, where n is the number of moles of the gas
* As more gas particles are introduced into the container, the frequency of their collisions increase
* Thus, the gas forces the container to expand until the pressure inside the container becomes the same as that of the outside
* STP – Standard Temperature Pressure
* Temperature – 0°C or 273.15 K
* Pressure – 101.3 kN m–2 (1 atm)
* Take note that in gas stoichiometry, the volume of one mole of any gas at STP is 22.4 liters

dalton’s law of partial pressure

* Partial pressure refers to the pressure that would be exerted by a gas in the mixture if it were the only gas present in the container


* The partial pressure of a gas is proportional to the fraction of its number of particles in the mixture expressed in moles
* Equation