Another Example
The gas in a balloon has a volume of 7.5 L at 100. kPa. The balloon is released
into the atmosphere, and the gas in it expands to a volume of 11. L. Assuming a
constant temperature, what is the pressure on the balloon at the new volume?
The volume of the gas has increased. Boyle’s Law predicts that the gas
pressure will decrease. So
The final pressure has decreased as predicted.Combined Gas Law
This is a combination of the two preceding gas laws. The formula is as follows:
TIP
In the combined gas law, all subscripts on the left side of the formula are 1’s and on the right
side are 2’s.Type Problem
The volume of a gas at 780. mm pressure and 30.°C is 500. mL. What volume
would the gas occupy at STP?
You again can use reasoning to determine the kind of fractions the
temperatures and pressures must be to arrive at your answer. Since the pressure is
going from 780. mm to 760. mm, the volume should increase. The fraction must
then be. Also, since the temperature is going from 30°C (303 K) to 0°C