Ethanol and Oxygen Reaction (Combustion) | CH3CH2OH + O2
Ethanol, a highly evaporative alcoholic compound, readily burns with oxygen gas and large amount of heat as a result. As chemical products, carbon dioxide and water are given if complete combustion is achieved. Otherwise, carbon monoxide can be given as another product if the supplied oxygen gas amount is not sufficient for a complete combustion. In this tutorial, we will study several combustion factors when ethanol is burned with oxygen gas.
CH3CH2OH + O2 → CO2 + H2O
In this tutorial, we will discuss followings.
Ethanol
Ethanol is an organic compound which contains two carbon atoms, two oxygen atoms and six hydrogen atoms. Pure ethanol is highly evaporative and vapor can be ignited readily if spark is found. Therefore, both ethanol liquid and ethanol vapor are combustible in the presence of oxygen gas and a spark is occurred. This is also a high risk becuase ethanol vapor can be spread out in a large space in a shorttime period if liquid ethanol container was not properly closed after an usage.
Stoichiometric balanced chemical reaction of ethanol and oxygen gases
One mol of ethanol reacts with three moles of oxygen gas and produce two moles of carbon dioxide and three moles of water.
CH3CH2OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
Change of oxidation numbers in ethanol combustion
Because, combustion process is a process of redox reactions, oxidation numbers of some elements are changed as below.
- In ethanol molecule, there are two carbon atoms and both exist at two different oxidation states (-3 and -1). However, both those carbon atoms are oxidized to carbon dioxide molecules. In carbon dioxide molecule, carbon is at +4 oxidation state.
- Oxygen is at 0 oxidation state in oxygen molecule (O2) and that those oxygen atoms are reduced to -2 oxidation state.
Thermal energy and heat generation
Standard enthalpy of combustion of ethanol (ΔHc0(CH3CH2OH,(l))) = -1370.9 kJ mol-1
Health and safety
Ethanol is a highly inflammable liquid and also pure ethanol liquid is very evaporative at room temperature. Therefore, ethanol vapor can be spread in a large space in a short time period and a small spark is enough to start a fire. So, everyone need to follow safety precautions in using of ethanol liquid in any requirement.
Questions
What will happen if there is excess oxygen gas than stoichiometric ratio?
Usually in a combustion process, there should be more oxygen gas amount than stoichiometric ratio for a successful combustion. For ethanol, it is better if there are 3.5 moles of oxygen gas instead of 3.0 moles for 1 mol of ethanol to increase the reaction rate.
Chemical equation for ethanol (CH3CH2OH) vaporizing
CH3CH2OH(l) → CH3CH2OH(g)
Ethanol is highly evaporative chemical and liquid phase is readily converted to gaseous phase.
How to handle ethanol to prevent explosion in laboratories?
Accumulation of ethanol vapor in a confined space is a huge risk if any spark is initiated. If you feel the ethanol odor, never switch on electrical switches which can be caused huge explosions. SO be careful to close lids of ethanol bottles to prevent accumulations of ethanol vapor.