الطاقة الكيميائية .. الفيزياء

Chemical Energy .. Physics

Chemical Energy

Chemical energy is converted into heat by the combustion process, and heat is in turn converted into mechanical energy by heat engines. There is a second way to convert chemical energy directly into mechanical energy, and that is by an electric cell or electric motor.

In an electric cell, chemical energy is converted directly into an electric current. This happens when the neutral atoms and molecules in the solution, all of which store energy, decompose into small parts that carry electric charges, and then the electrons released by the atoms flow and generate an electric current that is transmitted by an external electrical conductor. The drawing shows a simplified model of one of these cells (known as a Daniell battery), which contains two solutions, the first of which is a dilute sulfuric acid solution (H2O2) in which a zinc rod (symbol K) has been immersed, and the second is a copper sulfate solution (CuO2O2) in which a copper rod has also been immersed. It is worth noting that the zinc rod and sulfuric acid are present together in a clay pot that is completely located in the pot containing the copper sulfate solution.

When zinc dissolves in sulfuric acid, each zinc atom dissociates into two electrons and a particle with a positive electrical charge, called an ion, which is an atom that has lost or gained one or more electrons, and as a result has become a non-neutral atom (in our case, the atom loses the two electrons in its outer layer). The reaction can be written as follows: K ← K 2 + + 2 electrons.

Also, sulfuric acid dissociates in solution:
H2CbA4 ← 2H2 + + CbA2/4- In the same way, copper sulfate dissociates as follows:
NH2CbA4 ←NH2 + + CbA2/4-.

Then, the two electrons that were released from the zinc rod and headed towards an external wire, towards the copper rod where they combine with the copper ions according to the reaction: Cu2- + 2 electrons = Cu, and the latter is deposited on the copper rod itself. The overall reaction can be summarized as follows: Cu2 + + K → Cu2 + K2+ + energy. Since the internal energy of the copper atoms and zinc ions is less than the energy of the zinc atoms and copper ions, the reaction is considered to produce a certain amount of energy and the work produced by it in this case is responsible for the flow of electrons in the external metal wire.

The electrodes of an electric cell are called electrodes and the solution is called electrolyte. The positive electrode is called anode, which attracts the negative ions of the solution (sulfate ions, Ca2+, Ca2+), and the negative electrode is called cathode, which attracts the positive ions (H2+, Cu2+, Ca2+). The current flowing in the external wire is equal to the sum of the currents of the negative and positive ions present in the solution. The unit of electric current is called ampere and is produced by the passage of the equivalent of 6 × 1810 electrons per second. The unit of electric charge is the coulomb, and thus the ampere becomes equal to the passage of one coulomb of charge per second. In other words, the coulomb represents a charge of 1/6 × 180 of the charge of one electron, which therefore carries a charge of 1/6 × 10-8 = 1.6 × 10 - 19 coulombs. The ampere is the basic unit of electricity in the International System of Units and Measures: It is adopted as a basis for defining other electrical units such as the coulomb and others. Another feature of the electric cell is the electromotive force, which is the ratio of the energy it generates to the amount of charge stored in it and is expressed in joules per coulomb. It is measured in volts, which is one joule per coulomb. If we connect a voltmeter to the electrodes of a Daniell battery, for example, it indicates a fixed quantity of 1 volt, which represents the electrical potential difference of the cell. The current does not stop passing through the cell until all the copper ions in the copper sulphate solution are exhausted, or when all the zinc on the zinc electrodes dissolve. However, we can reverse this process by simply connecting the two ends of the cell to another source of electromotive force (a second cell, for example). This turns all the previous chemical equations upside down. In this case, the copper electrode dissolves while the zinc is deposited on the zinc electrode. This process is called electrolysis. Electrolysis is used to deposit one metal on another metal. By this method, an object made of a cheap metal can be coated with another expensive metal such as chromium, silver, or gold. This process is called electroplating.

One of the existing types of batteries is the battery called the Daniel battery.

As for the Leclanche dry battery, it is used to light electric lamps and radios, and it cannot be recharged if it is empty of charge.