What keeps things cold?
The modern refrigerator takes advantage of the gas laws to remove heat from a system. Compressed gas in the coils (see above) is allowed to expand. This expansion lowers the temperature of the gas and transfers heat energy from the material in the refrigerator to the gas. As the gas is pumped through the coils, the pressure on the gas compresses it and raises the gas temperature. This heat is then dissipated through the coils into the outside air. As the compressed gas is pumped through the system again, the process repeats itself.
Combined Gas Law
To this point, we have examined the relationships between any two of the variables of
Sample Problem: Combined Gas Law
2.00 L of a gas at 35°C and 0.833 atm is brought to standard temperature and pressure (STP). What will be the new gas volume?
Step 1: List the known quantities and plan the problem.
Known

P1=0.833 atm 
V1=2.00 L 
T1=35∘C=308 K 
P2=1.00 atm 
T2=0∘C=273 K
Unknown

V2=? L
Use the combined gas law to solve for the unknown volume
Step 2: Solve
First, rearrange the equation algebraically to solve for
Now substitute the known quantities into the equation and solve.
Step 3: Think about your result.
Both the increase in pressure and the decrease in temperature cause the volume of the gas sample to decrease. Since both changes are relatively small, the volume does not decrease dramatically.
It may seem challenging to remember all the different gas laws introduced so far. Fortunately, Boyle’s, Charles’s, and GayLussac’s laws can all be easily derived from the combined gas law. For example, consider a situation where a change occurs in the volume and pressure of a gas while the temperature is being held constant. In that case, it can be said that
Summary
 The combined gas law shows the relationships among temperature, volume, and pressure.

P1V1T1=P2V2T2
Practice
Work on the problems at the link below:
http://misterguch.brinkster.net/WKS001_007_146637.pdf
Review
Questions
 What is the only thing held constant in a combined gas law problem?

If you want to solve for the volume of a gas
(V2) andP1 is greater thanP2 , would you expectV2 to be larger or smaller thanV1 ? 
What would be the equation for finding
P2 given all the other parameters?