physical or chemical reaction?

Question

1.Oxygen gas changes to ozone during thunderstorms.
2.Freezing rain develops when a warm air mass overrides a cold air mass.
3.Carbon dioxide is produced by the combustion of gasoline in an automobile engine.
4.Fog forms from water vapor when the temperature drops below the dew point.
5.Solid waste decomposes in landfills and produces methane gas.

Answer 1

1. chem
2.phys
3. chem
4. phys
5. chem

Answer 2

The most important thing to know before answering these questions is: whether the change occurred involves molecular change or not. If yes--> chemical; and if no--> physical. Hence:
1. Oxygen: O2; while ozone: O3 --->chemical
2. water molecule does not change from ice to water to vapour ---> physical
3. "Carbon dioxide is produced "---> chemical
4. See #2---> physical
5. "decomposes" & "produces methane gas"---> chemical

Answer 3

The actual process of evaporation is physical but the reaction between the water and iron/salt mixture is chemical.