The heat of combustion refers to the heat released when a substance completely reacts with oxygen. Generally, it is measured by the amount of unit substance, unit mass or unit volume energy released by fuel combustion.
Combustion reaction is usually a reaction in which hydrocarbons burn in oxygen to produce carbon dioxide and water and give off heat. The heat of combustion can be measured by bomb calorimeter, or it can be directly looked up and then subtracted to get the enthalpy of formation of reactants and products.
Definition.
At 25℃ and 100kPa, (the old standard configuration pressure is 1 ATM =1kpa, that is,1standard atmospheric pressure, the new standard configuration pressure is changed to1bar =/kloc-0. Peking University Publishing House, Principles of General Chemistry (4th Edition), page 85, notes 1) 1mol The heat released when a pure substance is completely burned to form a stable compound is called the heat of combustion of the substance, and the unit is kJ/mol.
Key points:
1, the specified pressure is 100kPa, and the heat released by the reaction is measured. Because the pressure is uncertain, the reaction calorific value is different.
2. Specify the amount of combustible materials as 1mol. (comparable).
3. It is stipulated that stable compounds must be generated, because even the same amount of pure substances, the heat released by different gases is different under the same pressure, for example, the heat released by the combustion of Mg(s) in O2(g) is different from that released by the combustion of Mg(s) in Cl2(g). In order to unify the standards, it is stipulated to generate compounds.
4. It is stipulated that the standard is the heat released by the stable compound produced by the complete combustion of combustible materials. For example: H2S (g)+1/2o2 (g) H2O (l)+s↓; Δ h1,because the generated S is not completely burned, the heat Δ h1released by this reaction cannot be used as the combustion heat of H2S, when H2S (g)+3/2O2 (g) = = H2O (L)+SO2 (g).
Δ H2, when water is in a stable liquid state, also generates a stable oxide SO2, so Δ H2 at this time is the combustion heat of H2S. In addition, for water, the heat released by 1mol combustible will inevitably generate liquid water, which can be called combustion heat, but gaseous water cannot.