Complete combustion
Alcohols burn completely in excess oxygen to form carbon dioxide and water.
- Reagents
- oxygen
- Conditions
- ignite in excess oxygen
- Reaction class
- combustion
- Equation
- CnH(2n+2)O + (3n/2)O2 -> nCO2 + (n+1)H2O
Overview
Alcohols burn completely in excess oxygen to form carbon dioxide and water.
Transformation
- Equation
- CnH(2n+2)O + (3n/2)O2 -> nCO2 + (n+1)H2O
- Reagents
- oxygen
- Environment
- ignite in excess oxygen
- Reaction class
- combustion
- Mechanism
- combustion
- Evidence level
- textbook core
Reference procedure
Alcohol combustion: energy measurement
Alcohol + oxygen → carbon dioxide + water under complete combustion
Materials and quantities
- Specified alcohol fuels
- Known mass of water
Apparatus
- Spirit burners with caps
- Balance
- Water container and thermometer
Procedure
- Keep water mass, burner distance and starting conditions comparable across fuels.
- Measure burner mass loss and water-temperature rise, then express the estimated heat transfer per mole of fuel.
Work-up and isolation
- Record soot and other evidence of incomplete combustion alongside the numerical result.
Critical controls
- Heat loss and fuel evaporation usually make the result less exothermic than an ideal combustion value.
- Measure temperature change and analyse combustion gases separately.
- Extinguish and cool burners before handling or refilling; never refill near a flame.
Practical techniques
Combustion calorimetry and uncertainty
Estimate energy transfer from fuel combustion using water-temperature rise and fuel mass loss.
Setup
- Measure the water mass and starting temperature, and weigh the capped burner.
- After controlled heating, extinguish the burner, mix the water and record the final temperature and burner mass.
- Use q = mcΔT and divide by moles burned, with a negative sign for the estimated combustion enthalpy.
Operating checks
- Heat loss, apparatus heating, evaporation and incomplete combustion affect the estimate.
- Report an experimental value and uncertainty; do not label it a measured standard enthalpy without the required conditions.
Scope and limitations
- Scope
- Saturated, acyclic monohydric alcohols undergo complete combustion in excess oxygen to form carbon dioxide and water.
- Limitations
- The displayed general equation uses the formula CnH(2n+2)O. Other alcohol subclasses require coefficients derived from their own molecular formula; incomplete combustion is not represented here.
Related reactions
- Chlorination: Alcohols → Chloroalkanes
Alcohols can be converted into chloroalkanes to create a better leaving group for downstream substitution.
- Chlorination with thionyl chloride: Alcohols → Chloroalkanes
Thionyl chloride converts alcohols into chloroalkanes with sulfur dioxide and hydrogen chloride as by-products.
- Bromination: Alcohols → Bromoalkanes
Bromide and acid conditions convert alcohols into bromoalkanes.
- Iodination: Alcohols → Iodoalkanes
Iodine and red phosphorus conditions convert alcohols into iodoalkanes.
- Hydrolysis: Chloroalkanes → Alcohols
The C-Cl bond can be displaced by hydroxide to form an alcohol.
- Hydrolysis: Bromoalkanes → Alcohols
The C-Br bond can be displaced by hydroxide to form an alcohol.
- Hydrolysis: Iodoalkanes → Alcohols
The C-I bond can be displaced by hydroxide to form an alcohol.
- Oxidation: Alcohols → Aldehydes
Controlled oxidation of a primary alcohol gives an aldehyde.
- Oxidation: Alcohols → Ketones
Oxidation of a secondary alcohol gives a ketone.
- Oxidation: Alcohols → Carboxylic acids
Full oxidation of a primary alcohol gives a carboxylic acid.
- Hydration: Alkenes → Alcohols
Catalytic hydration converts alkenes into alcohols.
- Dehydration: Alcohols → Alkenes
Dehydration converts alcohols into alkenes.
- Esterification co reactant: Alcohols → Esters
Alcohols combine with carboxylic acids to form esters.
- Hydrolysis co product: Esters → Alcohols
Hydrolysis of an ester also regenerates the alcohol component.
- Grignard carboxylation co reactant: Carbon dioxide → Carboxylic acids
Carbon dioxide plus a Grignard reagent gives a carboxylic acid after acidic work-up.
- Complete combustion: Alkanes → Carbon dioxide
Alkanes burn completely in excess oxygen to form carbon dioxide and water.
References
- Pearson Edexcel Level 3 Advanced GCE in Chemistry specificationPearson Education Limited · Pearson qualifications · 2024
Supports the textbook-core organic reaction routes used for displayed route and mechanism content.
- Comparing heat energy from burning alcoholsRoyal Society of Chemistry and Nuffield Foundation · RSC Education
Spirit-burner comparisons and post-16 evaluation of heat loss and incomplete combustion.
- Temperature change: combustion of ethanolRoyal Society of Chemistry · RSC Education
Mass loss, water-temperature measurements, energy calculations and experimental evaluation.