Gas Laws (Part 2): The Return of VOlume
Charles’ Law At constant pressure, the volume of a gas is directly proportional to its absolute temperature. In other words, if the Kelvin temperature of a gas increases, the molecules move faster, they push out on the object containing the gas, and the volume of the gas will also increase. The volume will decrease with a decrease in temperature, because of slower moving molecules. For this equation, temperature must be in Kelvin. Here you have a demonstration of Charles’ Law. The temperature is slowly increased, the volume reacts accordingly. The temperature increases, the particles will move faster, pushing out on the piston more. This causes the volume to expand, as long as the pressure remains constant. The mathematical relationship between volume and temperature is: |
GIF courtesy of iamtechnical.com
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Where V1 is the starting volume, T1 is the starting temperature, V2 is the final volume and T2 is the final temperature.
Example: An expandable piston holds a volume of 15 ml at 293 K. The temperature of the piston is reduced to 215 K. What is the new volume of the piston?
Answer: V1 = 15 ml, T1 = 293 K, V2 = ? ml, T2 = 215 K
Combined Gas Law
If none of the values (pressure, volume or temperature) can be kept constant, we can combine the three gas laws into one equation:
If none of the values (pressure, volume or temperature) can be kept constant, we can combine the three gas laws into one equation:
Example: A 3 m3 balloon at 300 K and 900 torr is changed to STP. What is the new volume of the balloon? (Hint: STP stands for Standard Temperature and Pressure, experimental conditions equal to 0 OC and 1 atm)
Answer: P1 = 900 torr, V1 = 3 m3, T1 = 300 K, P2 = 760 torr, V2 = ? m3, T2 = 273 K