Why Should We Care?
Next, open the Options menu and, under the Display tab, click “Atmosphere”. When the carbon dioxide molecule absorbs a photon of IR radiation, observe how energy is transferred between the carbon dioxide molecule and the other atmospheric gas molecules, and note the effect on the temperature of the atmosphere.
Worked Example
How does absorption of IR radiation by a greenhouse gas molecule cause the average kinetic energy of the atmospheric gas molecules to increase? Describe the energy conversions that occur, using the Collisional Heating Learning Tool. as required.
Click here to show answer
First, the radiant energy of IR radiation is converted into the kinetic energy of the greenhouse gas molecule, as the molecule experiences vibrational motion. Next, through collisions, the greenhouse gas molecule’s kinetic energy is transferred to other atmospheric gas molecules, which are not capable of absorbing IR radiation. The average kinetic energy of the other atmospheric gas molecules increases, which is measured as an increase in temperature. The transfer of energy from a vibrating greenhouse gas molecule to other atmospheric gas molecules is called collisional de-excitation.
Your Turn
Explain how the combustion of coal contributes to the warming of the atmosphere, by describing the energy transformations and transfers that take place at each step.
Click here to show answer
Upon combustion, the difference between the potential energies contained in the bonds of the coal and oxygen reactant molecules and the potential energy in the bonds of the carbon dioxide and water product molecules is converted to thermal and radiant energy. When carbon dioxide molecules in the atmosphere absorb IR radiation, radiant energy is converted into the kinetic energy of the vibrating carbon dioxide molecules. This kinetic energy is transferred to other gas molecules in the atmosphere, when a vibrating carbon dioxide molecule collides with other atmospheric gas molecules, causing the average kinetic energy of the molecules in the atmosphere to increase. The increase in average kinetic energy corresponds to an increase in temperature and the atmosphere warms.
