13-3: The Gas Laws

What are the Gas Laws?

• The Gas Laws: are mathematical representations of the interaction between the four variables of gas:

1) Pressure2) Volume3) Temperature4) Quantity of a Gas

The First Law: Boyle’s Law

• Robert Boyle (1627-1691): English Chemist/Physicist, one of the first scientists to note that gases particles are spread out from one another.

• Most famous experiment involved trapping air in a J-shaped tube, while changing its pressure and measuring its volume. The experiment included mercury inside the tube, which moved and balanced out between the two sides when Boyle increased the atm. pressure.

• But how did this help Boyle learn anything?

The Pressure-Volume Relationship

• Boyle wanted to know, “Is there a relationship between pressure and the volume of a gas?”

• The answer is YES!

What exactly is Boyle’s Law?

• Boyle’s Law states: “if the temperature of a given gas remains unchanged, the product of the pressure times the volume has a constant value.”

How Can Boyle’s Law Help You?

• Boyle’s law can help you to determine different qualities without having to measure them.

P1V1 = P2V2

What is the mathematical relationship between pressure and volume?

inverse

The Second Law: Charles’s Law

• Jacques Charles too determined a relationship between gas variables.

• He did this by performing an experiment in which he kept the amount of the gas and its pressure constant.

• He discovered that the results of his experiment, when graphed, made a straight line with a positive slope when volume was plotted against temperature.

The Temperature-Volume Relationship

• Charles proved that volume of a gas is directly proportional to its temperature.

• It was determined by scientists that the lowest temperature your can reach is absolute zero. Which is equal to -273.15oC.

• Matching absolute zero, you must have an absolute temperature. Since the Kelvin scale is only measured in positive units, and its zero coincides with absolute zero, you use this when relating temperature with volume.

But, What Is Charles’s Law?

• Charles’s Law States: “at constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature.”

V1T2 = V2T1

The Third Law: Avagadro’s Law

• We all know who the Italian Chemist, Amedeo Avagodro is, and what he discovered.

• However, he also created a hypothesis that puzzled scientists in his times, and wasn’t accepted until decades later!

The Amount-Volume Relationship

• Avagodro’s Law States: “equal volumes of gases at the same temperature and pressure contain an equal number of particles.”

• Avagadro’s Law also states two main points: 1) all gases show the same physical behavior, 2) the larger the volume of a gas, the greater number of particles within the gas.

The Fourth Law: Dalton’s Law

• John Dalton (1766-1844): English chemist who was one of the first scientists to consider mixtures of gases.

• After numerous experiments he was able to determine that each gas in a mixture exerts the same pressure that it would if it were alone (not in a mixture).

• Each gas gives a pressure in a mixture, they each give a Partial Pressure.

Dalton’s Law Of Partial Pressures

• Dalton’s Law Of Partial Pressure States: “the sum of partial pressures of all the components in a gas mixture is equal to the total pressure of the gas mixture”

• To sum it up in an equation, it is written like this:

PT=Pa + Pb + Pc + . . .

• Where PT equals the total of all pressures, and the sub letters mark a different gas in the mixture.