Evidence
Evidences of Chemical Reactions
All chemical bonds posses potential energy. In a chemical reaction this energy is changed when old bonds are broken and new bonds are formed. Chemical changes are different from physical changes. When a physical change occurs there is no breaking and forming of bonds. There are certain things that will help us identify if a chemical reaction has taken place. We call these evidences of chemical reactions. - Light is given off: Potential energy in valance electrons is released in the form of light.
- Gas is given off: Indicates an increase in kinetic energy of the atom (compound) as it is changed to a gas.
- Temperature change: Exothermic is an increase in the speed of the molecules (heat). Exothermic is the taking in of energy.
- Color change: the increase or decrease of potential energy stored in new bonds.
- Precipitate formed: increase or decrease of potential energy in new bonds formed.
- Electrical potential: The release of chemical bond energies to cause the movement of valence electrons.
Some chemical changes are easy to observe. The products formed
by the rearrangement of atoms look different than the reactants.
Other changes are not easy to see but can be detected in other ways.
Color Change Substances often change color during a chemical
reaction. For example, when gray iron rusts, the product that forms
is brown, as shown in the photograph below.
Formation of a Precipitate Many chemical reactions form products
that exist in a different physical state from the reactants. A solid product
called a may form when chemicals in two liquids react, as
shown in the photograph below. Seashells are often formed this way
when a sea creature releases a liquid that reacts with seawater.
Formation of a Gas Chemical reactions may produce a gas, like that
formed when antacid pills are mixed with stomach acid. The photograph
below shows an example in which carbon dioxide gas is
produced by a chemical reaction.
Temperature Change Most chemical reactions involve a temperature
change. Sometimes you can recognize the change when you see a
flame. Notice the burning of the metal magnesium in the photograph.
Other temperature changes are not immediately obvious. If you touch
concrete before it hardens, you may notice that it feels warm. This
warmth is due to a chemical reaction.
All chemical reactions, whether simple or complex, involve changes in substances. One or more starting substances, the reactants, are changed into one or more new substances, the products.
Reactants à Products
In a chemical reaction the ways in which atoms are joined together are changed. Bonds are broken and new bonds are formed as reactants are converted into products. The atoms are not created or destroyed. They are just rearranged.
Chemical reactions can be described in different ways. For example, we could say: "Iron reacts with oxygen to produce iron (III) oxide (rust)." Alternatively, we could identify the reactants and product in this reaction by writing a word equation.
Iron + oxygen à iron (III) oxide
In a word equation, the reactants are written on the left, and the products are written on the right. They are connected by an arrow ( à ) that is read as "yields" or "reacts to produce." Word equations communicate the reaction but can get cumbersome. To be more efficient chemists use chemical formulas for writing equations. For example the rusting of iron would be represented as follows:
Fe + O2 à Fe2O3
Equations that show just the formulas of the reactants and products are called skeleton equations. A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products. The physical state of a substance in a reaction can be indicated in the equation by using the following symbols: (s) for solid, (l) for liquid, (g) for gas, and (aq) for a solution in water. These usually follow the substance in the equation and can also be written as subscripts. To write a skeleton equation, you must write the correct formulas of the reactants and products with the reactants on the left side of the yield sign and the products on the right.
Just writing the skeleton equation of reaction does not always correctly communicate what is happening in the reaction. To represent chemical reactions correctly, equations must be balanced so that they show the amount of reactants and products in the reaction. In every balanced equation each side of the equation has the same number of atoms of each element. This is necessary to be consistent with the law of conservation of mass. Remember, in a chemical reaction, atoms are not created nor destroyed; they are simply rearranged.
hai zelvy... can you Give me examples of common chemical reactions in daily life?
BalasHapusHello Rini, the examples about chemical reaction in daily life such as
Hapus1. Photosynthesis
Scheme of photosynthesis in plants. The resulting carbohydrates are stored in or used by plants. Source: wikipedia.org
Photosynthesis is a process used by plants and other organisms to convert light energy, usually from the Sun, into a chemical energy that can then be liberated to fuel organism activity. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. In most cases, oxygen is also produced as a waste product. Most plants, mostly algae, and cyanobacteria do photosynthesis, and these organisms are called photoautotrophs. Photosynthesis maintains atmospheric oxygen levels and supplies all organic compounds and most of the energy needed for life on Earth.
Briefly, plants use a chemical reaction called photosynthesis to convert carbon dioxide and water into food (glucose) and oxygen. It is one of the most common daily chemical reactions and also one of the most important, because this is how plants produce food for themselves and animals and convert carbon dioxide into oxygen.
6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
2. Aerobic Cell Respiration
Aerobic respiration (red arrow) is the main means by which both fungi and plants utilize chemical energy in the form of previously made organic compounds through photosynthesis (green arrow). Source: wikipedia.org
Aerobic cellular respiration is the reverse process of photosynthesis in molecular energy coupled with the oxygen we breathe to release the energy needed by our cells plus carbon dioxide and water. The energy used by cells is the chemical energy in the form of ATP (adenosine triphosphate).
Aerobic respiration requires oxygen to produce ATP. Although carbohydrates, fats, and proteins are consumed as reactants, it is the preferred method of breaking pyruvate in glycolysis and requiring pyruvate to enter the mitochondria to be completely oxidized by the Krebs cycle. The products of this process are carbon dioxide and water, but the energy transferred is used to break strong bonds in ADP as a third phosphate group is added to form ATP, by substrate level phosphorylation, NADH and FADH2
Here is the overall equation for aerobic cell respiration:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (36 ATPs)
3. Anaerobic Respiration
Anaerobic Respiration
Anaerobic Respiration. Source: http://www.boundless.com
In contrast to aerobic respiration, anaerobic respiration represents a set of chemical reactions that allow cells to gain energy from complex molecules without oxygen. Cell muscles perform anaerobic respiration every time we get rid of oxygen which then reaches them, like during intense or prolonged exercise. Anaerobic respiration by yeast and bacteria used for fermentation, to produce ethanol, carbon dioxide, and other chemicals that make cheese, wine, beer, yogurt, bread, and many other common products.
The overall chemical equation for one form of anaerobic respiration is:
C6H12O6 → 2C2H5OH + 2CO2 + energy
Zelvy, please give me evedence that chemical reactions can change color
BalasHapusOkay, the evidence is An example of a chemical reaction that causes discoloration of the reacting agent is the reaction between the FeCl3 (brown) solution and the KSCN (colorless) solution.
HapusIf the FeCl3 solution is dropped into KSCN solution, a color change in the KSCN solution will occur. The chemical reaction equation is as follows.
Solution FeCl 3 + KSCN solution → Fe (SCN) 2+ + KCl solution
hi zelvyy,
BalasHapustell me,, example the rusting of iron would be represented as follows?
From my article point of you Word equations communicate the reaction but can get cumbersome. To be more efficient chemists use chemical formulas for writing equations. For example the rusting of iron would be represented as follows:
HapusFe + O2 à Fe2O3
hi zelvy, please give me explanation about evidences of chemical reactions. ? thanks
BalasHapusWell, All chemical bonds posses potential energy. In a chemical reaction this energy is changed when old bonds are broken and new bonds are formed. Chemical changes are different from physical changes. When a physical change occurs there is no breaking and forming of bonds. There are certain things that will help us identify if a chemical reaction has taken place. We call these evidences of chemical reactions.
HapusHai zelvy.
BalasHapuswhy In a chemical reaction the ways in which atoms are joined together are changed?? Thanks
Explain the definition of reactants and products and give examples
BalasHapusWhat happen if Noble gas and another make as evidence for reaction?
BalasHapusZelvy, why all chemical bonds have potential energy ?
BalasHapus