We explain that what are some examples of chemical energy? Chemical energy is what appears during a chemical reaction . When a substance comes into chemical contact with a different one, the bonds between the atoms (or molecules) that form it are broken. This break releases the energy that held them together, making it generally available as heat .
When the particles of the first substance are free, they tend to bond with the atoms or molecules of the other to form the products : new chemical compounds. At this junction, an emission or absorption of chemical energy also occurs. According to Physicochemistry, there are several types of chemical energy according to the nature of the reaction.
Types of chemical energy
Chemical energy, and other forms of energy that involve heat, are expressed with a quantity called enthalpy . Enthalpy is a portion of energy that occurs in a process at constant pressure, and is represented by the letter H . H values are not used as much for each step of the process; rather, it is useful to know the total change in the process:
Δ H = final H – initial H
Δ H = H 2 – H 1
The general types of chemical energy are:
- Solution enthalpy
- Enthalpy of combustion
- Formation enthalpy
- Enthalpy of reaction
In the International System of Units (SI), the units for energy are Newton-meters (Nm) or Joules (J). As they refer to energies of chemical reactions and these are interpreted with moles, the energy units are for each mole of reactants or products:
ΔH: J / mol (Joules per mole), for small quantities
o ΔH: KJ / Kmol (KiloJoules per Kilomole), for large quantities
They can also be transformed to J / g and KJ / Kg, but that will depend on knowing the exact value, and transforming the moles into grams by means of the molecular weight.
Solution enthalpy occurs when an ionic substance , such as acids, bases, and salts, is placed in water and dissolved . What happens there is that its charged particles or ions separate from its material to be dispersed in the water. This leads to a release or absorption of heat. Water contains its own ions: hydrogen H + and hydroxyl OH – , which also interact.
The value of the solution enthalpy for a given substance can be consulted in physicochemical tables , which indicate it for various atmospheric pressures and concentrations. The enthalpy of solution for sulfuric acid H 2 SO 4 is one of the highest values, since it is a strong acid and dissociates violently easily in water.
Enthalpy of combustion
The enthalpy of combustion appears when a fuel combines with oxygen , initiating the reaction with a spark. A fuel is organic matter (that is, made up mainly of covalent chains of carbon and hydrogen) that when it receives a spark or flame comes into contact with the oxygen in the air and begins to decompose, releasing a lot of heat.
In addition to heat, a combustion reaction causes the fuel to release gases such as carbon dioxide (CO 2 ) and carbon monoxide (CO), and water vapor. The enthalpy of combustion can be consulted in tables of physicochemical books, and its values are available from methane (CH 4 ), the simplest hydrocarbon, to more complex organic compounds.
The enthalpy of formation is one that describes how much energy has been required for a chemical to form or create . For chemical elements, this has no value: ΔH F = 0, because they are already naturally as they are.
For the creation of the molecules of chemical compounds, a chemical reaction has already been involved, so their enthalpies can be measured. Their values can be consulted in physicochemical books.
Enthalpy of reaction
The enthalpy of reaction is, as such, the energy that is involved in the transformation of substances. Its value indicates the energy change that has occurred, including both in the breaking of the bonds between atoms, and in the formation of the products. Their values can be calculated based on the enthalpies of formation of each of the participating substances, as follows:
ΔH reaction = ΔH Products – ΔH Reagents
This is supported by physicochemical books, which will indicate the enthalpies of formation of each of the participating substances.
Examples of chemical energy
Chemical energy is written with a negative sign when the chemical reaction is exothermic (heat is released), and with a positive sign when the chemical reaction is endothermic (absorbs heat).
- Energy of formation of Ammonia NH 3 (g): -11,040 cal / mol
- Energy of formation of sulfuric acid H 2 SO 4 (l): -193,910 cal / mol
- Carbon dioxide formation energy CO 2 (g): -94,050 cal / mol
- Energy of formation of Silver oxide Ag 2 O (s): -7,310 cal / mol
- Energy of formation of Ferric oxide Fe 2 O 3 (s): -196,500 cal / mol
- Energy of formation of sodium chloride NaCl (s): -98,230 cal / mol
- Energy of formation of sodium hydroxide NaOH (s): -102,000 cal / mol
- Combustion energy of Methane CH 4 (g): -212,800 cal / mol
- Combustion energy of Ethane C 2 H 6 (g): -372,820 cal / mol
- Combustion energy of Propane C 3 H 8 (g): -530,600 cal / mol
- Combustion energy of Butane C 4 H 10 (g): -687,980 cal / mol
- Combustion energy of Pentane C 5 H 12 (g): -845,160 cal / mol
- Combustion energy of Ethylene C 2 H 4 (g): -337,230 cal / mol
- Combustion energy of Acetylene C 2 H 2 (g): -310,620 cal / mol
- Combustion energy of Benzene C 6 H 6 (g): -787,200 cal / mol