Practice
To change a temperature expressed in degrees Celsius to a temperature on the Kelvin scale, what must be done to the Celsius temperature?
Answer
add 273
Why must we use the Kelvin scale in gas law problems?
Answer
so that no temperature has a negative value
To check your solutions to the problems, click the words Hint, Formula and Variables, and Answer.
The volume of a sample of gas is 2.00 L when the temperature is 11.0 °C. While the pressure remains constant, the temperature is changed to a new value, which causes the volume to become 3.00 L. What was the temperature changed to?
Hint
Notice that the temperature given is in degrees Celsius. Kelvin temperatures must be used in all gas laws. This temperature must be converted to Kelvin by adding 273 to it.
Formula and Variables
T1 = 11 °C + 273 = 284 K
V1 = 2.00 L
T2 = ?
V2 = 3.00 L
V1T2 = V2T1
T2 = (V2T1) / V1
Answer
T2 = (3.00L x 284 K) / 2.00 L
T2 = 426 K
Which law was this an example of?
answer
This is an example of Charles’ law
The volume occupied by a sample of gas is 480 mL when the pressure is 115 kPa. What pressure must be applied to the gas to make its volume become 650 mL?
Which law was this an example of?
Formula and Variables
P1 = 115 kPa
V1 = 480 mL
P2 = ?
V2 = 650 mL
P1V1 = P2V2
P2 = (P1V1) / V2
Answer
P2 = (P1V1) / V2
P2 = (115 kPa x 480 mL) / 650 mL
P2 = 85 kPa
Which law was this an example of?
Answer
This is an example of Boyle’s Law.
The volume occupied by a sample of gas is 240.0 mL when the pressure is 1.20 atm. What volume, at constant temperature, will the gas occupy when the pressure is decreased to 0.860 atm?
Formula and Variables
P1 = 1.20 atm
V1 = 240.0 mL
P2 = 0.860 atm
V2 = ?
P1V1 = P2V2
v2 = (P1V1) / P2
Answer
V2 = (P1V1) / P2
V2 = (1.20 atm x 240.0 mL) / 0.860 atm
V2 = 335 mL
The volume of a sample of gas is 25.0 mL when the temperature is 270 K. If the temperature is changed to 30.0 °C, what will be the new volume occupied by the gas assuming that the pressure remains constant?
Hint
Notice that the second temperature given is in degrees Celsius. Kelvin temperatures must be used in all gas laws. This temperature must be converted to Kelvin by adding 273 to it.
Formula and Variables
T1 = 270 K
V1 = 25.0 mL
T2 = 30 °C + 273 = 293 K
V2 = ?
V1T2 = V2T1
V2 = (V1T2) / T1
Answer
V2 = (V1T2) / T1
V2 = (25.0 mL x 293 K) / 270 K
V2 = 28.1 mL
When the volume of a sample of gas is divided by the temperature of the gas, the result is 1.33 mL / K. The temperature of the gas is changed to a new value, which happens to be 411 K while the pressure is kept constant. What volume does the sample of gas occupy at 411 K?
Note
Don’t confuse lowercase k, which refers to a constant value, with uppercase K, which refers to Kelvin.
Formula and Variables
(V/T) = k
(V/T) = 1.33 mL/K
Answer
V = 1.33 mL/K x 411 K
V = 547 mL
When the pressure exerted by a sample of gas is multiplied by the volume occupied by the sample, the result of this multiplication is 1.60 x 105 mm Hg·mL. The pressure exerted by the sample changes to a new value, which happens to be 750 mm Hg. What volume will the sample occupy at this pressure, assuming that temperature remains constant?
Formula and Variables
PV = k
Answer
750 mm Hg x V = 1.60 x 105 Hg x mL
V = (1.60 x 105 mm Hg x mL) / 750 mm Hg
V = 213 mL