12704165
| Pregunta | Respuesta |
| What are the properties of chlorofluorocarbons (CFCs)? | Very stable Volatile Non-flammable Non-toxic |
| What were CFCs used in? | Fridges Aerosol cans Dry cleaning Air-conditioning |
| What was the problem with using CFCs? | CFCs were destroying the ozone layer |
| Complete the sentences: The ozone layer is in a layer of the atmosphere called the ______________. It contains most of the atmosphere's ________ molecules (O₃) and acts as a ___________ sunscreen. It absorbs a lot of the ____ radiation which can cause sunburn or even ________ ___________. | The ozone layer is in a layer of the atmosphere called the STRATOSPHERE. It contains most of the atmosphere's OZONE molecules (O₃) and acts as a CHEMICAL sunscreen. It absorbs a lot of the UV radiation which can cause sunburn or even SKIN CANCER. |
| Ozone is formed naturally in what type of reaction? | Free radical substation |
| Describe the formation of ozone from oxygen, giving the symbol equations | An oxygen molecule is broken down into two free radicals by UV radiation: O₂ + hv --> 2O• The free radicals attack other oxygen molecules, forming ozone: O₂ + O• --> O₃ |
| Describe the process by which CFCs destroy the ozone layer, including the chemical equations | CFCs absorb high-energy UV radiation and split to form chlorine free radicals: CF₂Cl₂ + hv --> CF₂Cl• + Cl• These free radicals catalyse the destruction of ozone, setting up a chain reaction: Cl• + O₃ --> O₂ + ClO• ClO• + O• --> O₂ + Cl• The chlorine radical is regenerated and goes on to attack another ozone molecule |
| Give the overall symbol equation for the destruction of ozone | O₃ + O• --> 2O₂ |
| Name another type of compound that destroys ozone, other than CFCs | Nitrogen oxides (NO• free radicals) |
| Nitrogen oxides are produced by... | Car and aircraft engines Thunderstorms |
| TRUE OR FALSE: NO• free radicals affect ozone in the same way as chlorine radicals | TRUE |
| CFCs were banned because of the environmental causes. There were, however, a few permitted uses. What were they? | Medical inhalers Fire extinguishers used in submarines |
| Name three alternatives to CFCs | HCFCs (hydrochlorofluorocarbons) HFCs (hydrofluorocarbons) Hydrocarbons |
| On average, how many years does it take for CFCs to leave the atmosphere? | 90 years |
| Why are HCFCs, HFCs and hydrocarbons only temporary alternatives to CFCs? | HCFCs still damage the ozone layer (though their effect is much smaller than that of CFCs) HCFCs, HFCs and hydrocarbons are greenhouse gases (they contribute to global warming) |
| TRUE OR FALSE: HFCs don't affect the ozone layer | TRUE They don't contain chlorine (no Cl•) |
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