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Gas molecules, absolute zero and the Kelvin scale
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Gas pressure comes from molecules hitting the walls of their container. Temperature measures how fast they move.
Gas pressure
Molecules in a gas move in random directions at high speeds.
When they hit the walls of their container they exert a force, and force on an area is pressure.
When they hit the walls of their container they exert a force, and force on an area is pressure.
Absolute zero and kelvin
As a gas cools, its molecules slow down. At absolute zero, −273 °C, they have the least possible kinetic energy, so nothing can be colder.
The Kelvin scale starts at absolute zero (0 K). One kelvin is the same size as one degree Celsius.
K = °C + 273 and °C = K − 273
The Kelvin scale starts at absolute zero (0 K). One kelvin is the same size as one degree Celsius.
K = °C + 273 and °C = K − 273
Temperature and molecules
Heating a gas increases the average speed of its molecules.
The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules: double the kelvin temperature, double the average kinetic energy.
The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules: double the kelvin temperature, double the average kinetic energy.
Convert 27 °C to kelvin, and 400 K to degrees Celsius.
- 27 + 273 = 300
- 400 − 273 = 127
Answer: 300 K; 127 °C
Gas molecules move randomly and hit the walls, causing pressure. Absolute zero is −273 °C (0 K). K = °C + 273. Heating increases the average speed of molecules; the Kelvin temperature is proportional to their average kinetic energy.
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