A chemical reaction is a chemical change event from a reacting substance into a reaction-resulting substance.
What are Chemical Reactions?
A chemical reaction is the event of chemical change from reacting substances (reactants) to the reaction-resulting substances (products). In chemical reactions always produce new substances with new properties. Chemical reactions are written using elemental symbols. Let’s see how to express a reaction using a symbol.
Pay attention to the reaction of mercury oxide that produces the following mercury and oxygen.
HgO —— Hg + O2
The chemist will translate the above symbols as follows. “An HgO molecule consisting of one mercury atom (Hg) plus one oxygen atom (O), produces (——) one molecule consisting of one mercury atom (Hg) plus one molecule consisting of two oxygen atoms (O2)”.
A combination of symbols that indicate a chemical reaction is called a chemical equation. Substances that react on the left arrow are called reagents while the substance on the right of the arrow is called the result of the reaction. So, the HgO in the chemical equation above is a reagent. Hg and O2 are the result of a reaction.
The law of conservation of matter states that in ordinary chemical reactions no material is lost although it may change. The number of atoms in the reagent remains the same as that produced, no matter how much they change to form a new molecular pattern. If an equation meets these conditions, it can be said that the equation is balanced.
What about equations
HgO —— Hg + O2?
To balance the equation, we add the number 2 before HgO and the number 2 again before Hg. 2HgO means two molecules consisting of one mercury atom and one oxygen atom each. That equation is now:
2 HgO – 2 Hg + O2
In other words, two mercury oxide (HgO) molecules, each consisting of one mercury atom and one oxygen atom, produce two mercury molecules, each consisting of one mercury atom plus one oxygen molecule, consisting of two oxygen atoms.
The equation is now balanced, on the left there are two mercury atoms and two oxygen atoms, as well as on the right. Note that in the reaction results are written 2 Hg, not Hg2. This is because mercury molecules consist only one mercury atom.
If the number 2 we write below, then we say that the molecule contains two atoms and this is wrong. Remember that in balancing equations we should not replace molecules. We can only change the number of molecules.
Chemical Reaction Characteristics
Chemical reactions in the real world are very easy to find, for example when burning paper. The paper was originally still a white sheet, after being burned using fire, then the paper was burnt.
In addition, when we boil water. Water forms the next liquid into gas and moisture after boiling in a saucepan placed on the stove.
These events are characteristic of the presence of chemical reactions in real terms. But for the formation of the product the result we are very difficult to see it. Here are the characteristics of chemical reactions:
#1. Color Change
Chemical molecules/compounds have the ability to absorb color and emit color depending on the substances. This ability can also be affected by an event.
For example: Iron reactants that are too long left in the open and in a wet state will rust (yellow-brown).
#2. Temperature Changes
Chemical molecules/compounds have deep energy in the form of chemical bonds. These bonds require energy or can release energy.
When many bonds are formed, then the energy will be released as the temperature rises. For example: Burning LPG gas on the stove.
#3. The Appearance of Gas Bubbles
Gas in chemical reactions may appear due to heating.
For example: The baking soda molecules / compounds on the dough when warming will release gas so that the cake expands.
#4. Volume Changes
When the product results from a chemical reaction is formed, it means that the amount of reactant volume is reduced. For example: The volume of lake water decreases during the summer.
#5. Precipitate Formed
The precipitate is a residual chemical reaction substance between two solutions that become solid. This substance can occur because the solution is too saturated.
#6. Light Emitting
Chemical reactions sometimes release energy in the form of light
For example: Reaction to the sun
#7. Conductivity Changes
Chemical reactions affect changes in conductivity (the ability to conduct heat).
#8. Taste Change
Chemical reactions when chewing rice cause a sweet taste when touching the tongue.