The Gas Laws

What are the Gas Laws?  The gas laws deal specifically with volume, temperature, and pressure.  Changes in volume, temperature, and pressure have predictable effects on the behavior of gases  Volume, Temp., Pressure, and the # of particles in a container of gas all affect one another

Pressure  Pressure is the result of a force distributed over an area  Pressure is measured in atmospheres (atm)  Collisions between particles of a gas and the walls of the container cause the pressure in a closed container of gas

Pressure in Airplanes  Before an airplane takes off, the plane must regulate its air pressure inside the cabin  As the airplane takes off higher into the sky, the pressure on the outside of the plane is too dangerous, so the cabin must keep a safe, regulated air pressure sealed inside  A difference in pressure is also why your ears “pop”

Factors that affect gas pressure  Factors that affect the pressure of an enclosed gas are its temperature, its volume, and the number of particles  Remember: in a gas the particles are constantly moving and bumping into one another

Temperature  The constant motion of particles in a gas cause the gas to heat up, this is due the gas’ kinetic energy.  As temperature rises, the average kinetic energy of the gas particles also increases

Temperature cont.  The increase in the number particle collisions, along with the increase in the force of the collision causes an increase in pressure within the container  Raising the temperature of a gas will increase its pressure if the volume of the gas and the number of particles are constant (Stay the same)

Volume  As the volume in a container of gas is decreased, particles of trapped air start to collide more often with one another and the container’s walls

Volume cont.  Reducing the volume of a gas increases its pressure, as long as the temperature of the gas and the amount of gas particles remains constant (stays the same)

Number of Gas Particles  When you add more gas particles to a container of gas, the pressure will start to increase  Think about adding more air to a balloon that is already full, the pressure increases and eventually the balloon will pop

Number of Gas Particles Cont.  Increasing the number of particles in a container of gas will increase the pressure of the gas, as long as the temperature and volume remain constant (stays the same)

Charles Law  Named after French, physical scientist Jaques Charles.  His inventions include the helium balloon  He is also known for his study on how gases behave

Charles Law cont.  Charles law states: “The volume of a gas is directly proportional to its temperature (in kelvins, k) if the pressure and the number of particles of a gas are constant.”

Charles Law cont.  To convert Celsius to Kelvin, simply add 273 to the temperature in Celsius  Example: 30°C = = 303°K

Charles Law cont.  The equation for Charles Law looks like this:

Boyle’s Law  Robert Boyle was an Irish scientist  He was the first to describe the relationship between the pressure and volume of a gas

Boyle’s Law cont.  Boyle’s Law states: “The volume of a gas is inversely proportional to its pressure if the temperature and number of particles in a gas remain constant.”

Boyle’s Law  Boyles Law is expressed like this:

The Combined Gas Law  The relationships described by Boyle’s Law and Charles’ Law can be described by a single law  As long as we know the number of particles remains constant, we can use the combined gas law

The Combined Gas Law cont.  The Combined Gas Law looks like this:

Combined Gas Law cont.

The Ideal Gas Law  Now, all this math and chemistry is probably making your brain want to explode  Good news, there is a simpler gas law!

The Ideal Gas Law  The Ideal Gas Law looks like this  PV = nRT  R =  P = Pressure  V = Volume  T = Temperature  n = number of moles in a substance

What is R?  R will always be 0.082, it’s a constant

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