4A 2.0 - Alkane Reactions
- Created by: Strelly22
- Created on: 27-03-21 11:19
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- Combustion of alkanes
- Alkane Reactions
- Reactions of alkanes with halogens
- CH4 + Cl2 ? CH3Cl + HCl
- need uv light
- substitution as one of the H's has been replaced by a Cl
- radical substitution
- Radical = a species with an unpaired electron
- radical is a dot
- 3 stages
- 1. initiation
- homolytic fission (even splitting)
- generates radicals
- uv light needed to provide the activation energy
- 2. propagation
- for every radical used in the reaction, a new radical is produced
- example
- a) Br. + CH4 ? HBr + CH3.
- b) CH3. + Br2 ? CH3Br + Br.
- 3. termination
- 2 radicals combine to give a product that is not a radical
- example
- a) Ch3. + Br. ? CH3Br
- b) CH3. + CH3. ? CH3CH3
- c) Br. + Br. ? Br
- 1. initiation
- limitations
- further substitution can occur
- substitution at different positions on the C chain can occur
- the C chain may change in length (eg. double) it is difficult to synthesis only 1 desired product
- Radical = a species with an unpaired electron
- CH4 + Cl2 ? CH3Cl + HCl
- Reactions of alkanes with halogens
- Complete
- Plentiful supply of oxygen
- General Formula:
- CxHy + (x+1/4y) O2 ? xCO2 + 1/2y H2O
- Incomplete
- Limited oxygen supply
- incomplete combustion is dangerous because:
- CO is toxic and causes death by preventing haemoglobin from carrying oxygen to respiring tissues
- Is colourless and odourless ? presence difficult to detect
- must heat with air holoe open on bunsen
- if closed: yellow flame because of the glowing soot particles. the outside of the glassware will become sooty
- why do diesel cars produce more soot than petrol
- diesel contains longe C chains than petrol so requires more moles of oxygen per mole f fuel to combust fully.
- engine technologies also play a part in controlling combustion of fuels, so is a bit more complex
- Alkane Reactions
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