The gas laws are a set of formulas used to calculate changes in temperature, volume or pressure.
While there are many gas laws, these are the four most used in these calculations.
q
THE
COMBINED GAS LAW FORMULA
q THE IDEAL GAS LAW FORMULA
P V = n R T
The behavior of gases is very different from the behavior of solids and liquids. The molecules of gases have a lot more kinetic energy (energy of motion). Unlike the other forms of matter, gas molecules do not stay togather but are free to move inside their container.
We can measure the sides of a solid and calculate its volume. When the solid is moved to a different space, the volume does not change. The same would be true for a liquid. However, when gas is moved to a larger or a smaller container , while the mass does not change the volume of the gas does change.
A different set of equations must be used for gases because their properties are so different from solids and liquids. While we are more familiar with calculations of mass, volume and density of solids and liquids, using the gas laws is no more complicated then these.
Rules for using
the Gas Laws:
ü Temperature: Change all temperatures into Kelvin.
ü Pressure: Convert all pressures to atmospheres.
ü Volume in Liters (L) or milliliters (ml) 1 L = 1000 ml
ü If a gas is at STP: this means Standard Temperature and Pressure.
Temperature = 0oC = 273 K
Pressure = 1 atm
ü For an Ideal Gas, collisions of molecules are perfectly elastic. This means that no energy is lost in the collision. This condition does not effect the calculations in any way. In reality a small amount of energy is lost to heat. The amount is negligible, but to be chemically correct the term ‘Ideal Gas’ is frequently included.
Boyles Law:
Robert Boyle noticed that for an Ideal Gas if the temperature did not change:
¨ to increase the pressure he had to decreased the volume.
¨ to decrease the pressure he had to increase the volume.
From this relationship Boyle was able to write the mathematical formula that is now known as Boyles Law:
.
When to use Boyles
Law:
§ If the TEMPERATURE is constant.
AND
§ You need a missing pressure.
OR
§ You need a missing temperature.
Charles’ Law
Jacques Charles noticed that for an Ideal Gas if the temperature did not change:
¨ when the temperature increases the volume also increases.
¨ when the temperture decreases the volume also decreases.
From this relationship Jacques Charles was able to write the mathematical formula that is now known as Charles’ Law:
.
When to use Charles’
Law:
§ If the PRESSURE is constant.
AND
§ You need a missing volume
OR
§ You need a missing temperature.
GAY-LUSSAC ‘S
LAW
For an Ideal Gas, Gay-Lussac noticed that if the volume does not change:
¨ when the pressure increases the temperature also increases.
¨ when the pressure decreases the temperature also decreases.
.This mathematical relationship is often called Gay-Lussac’s Law:
When to use Gay-Lussac’s
Law:
§ If the VOLUME is constant.
AND
§ You need a missing pressure
OR
§ You need a missing temperature.
The Combined Gas Law
Putting all the laws together will result in the Combined Gas Law. The algebraic calculations show how the laws were combined into a single law.
The Mathematics:
The Combined Gas Law can be used to derive any of the three laws when one of the three variables, pressure, temperature or volume remains unchanged. The term would simply cancel and the remaining formula would be one of the relationships that considered a GAS LAW .
Visit this . Combined
Gas Law Deriving Formula link to
see how these were derived.
When to use The COMBINED
GAS LAW FORMULA
§ If the VOLUME is not constant.
AND
§ the PRESSURE is not constant
AND
§ the TEMPERATURE is not constant
AND
you need a missing temperature OR volume OR pressure
V1P1 = V2P2
T1 T2
V1 = Starting Volume V2= New Volume
P1= Starting Pressure P2= New Pressure
T1= Starting Temperature T2= New Temperature
Learning Module:
Gas Laws
Created by Susan Christenbury
Report any problems or errors
to: schrist50@yahoo.com