ATOMIC STRUCTURE

ATOMIC STRUCTURE
A. BASIC UNDERSTANDING
1. Elementary particles: particles are composed of atoms forming
electron, proton neutron den.
1. Proton: forming atomic particles have the same mass
one sma (amu) and charged +1.
2. Neutron: particles forming a sma atomic mass (amu) and
neutral.
3. Electron: atom forming particles that have no mass and
charged -1.
2. The nucleus: a positively charged nucleus, consisting of protons and
neutrons.
3. Notation elements:
Zaa by X: sign atoms (elements)
Z: atomic number = number of electrons (e)
   = Number of protons (p)
A: mass number = number of protons + neutrons
In neutral atoms, applies: the number of electrons = number of protons.
4. No neutral atoms: electrically charged atoms due to excess or
electron deficiency when compared with the neutral atom.
Positively charged atoms when the electron deficiency, called cations.
Negatively charged atoms when an excess of electrons, called anions.
Example:
- Na +: cation with one electron deficiency
- Mg2-: cation with a shortage of 2 electrons
- Cl-: anion with an excess of one electron
- O2: anion with an excess of two electrons
5. Isotopes: elements of the same atomic number, but different numbers
mass.
Example: oxygen isotopes: 8O16 8O178O18
6. Isobar: elements of the same mass number, but different numbers
atom.
Example: 27CO59 with 28Ni59
7. Isoton: elements with the same number of neutrons.
Example: 6C13 with 7N14
8. Iso electron: atom / ion with the same number of electrons.
Example: Na + with Mg 2 +
K + with Ar
B. MODEL ATOM
1. MODEL ATOM JOHN DALTON
- Atom is the smallest part of an element
- Atoms can not be created, destroyed, divided, or changed to
other substances
- Atoms of an element are the same in all respects, but different
atoms of other elements
- Chemical reaction is a process of merging or splitting of the atom
elements are visible
Dalton's atomic theory Weakness: can not distinguish sense
atoms and molecules. And the atom was not the smallest particles.
ATOM 2.MODEL J.J. THOMPSON
- Atom is a positively charged sphere and inside spread
electrons are like raisins
- The amount of positive charge with a negative charge, so that the atoms are
neutral
3. RUTHERFORD ATOM MODEL
- Atom consists of a very small nucleus with a positive charge
mass is the mass of the atom
- Electrons moving around the nucleus in an atom is
- The number of electrons in an atom equal to the number of protons in the nucleus and
This corresponds to the number
atom
4. MODEL ATOM Bohr
- Electrons surrounding the nucleus is in the energy levels
(Skin) without specific
absorb or emit energy
- Electrons can move from the outer skin to the deeper skin
radiated energy, or vice versa
C. QUANTUM NUMBERS
To determine the position of an electron in an atom, used 4
quantum numbers.
1. The principal quantum number (n): realizing the electron trajectories in
atom.
n has a price of 1, 2, 3, .....
- N = 1 corresponds to the K shell
- N = 2 correspond to the L shell
- N = 3 corresponds to the skin M
- And so on
Each skin or any number of energy levels occupied by electrons.
The number of electrons that can occupy maksimmm energy levels
must satisfy the Pauli formula = 2N2.
2. Azimuthal quantum number (l): indicate sub skin where
electrons that move also shows a sub-skin
compilers of the skin.
Azimuthal quantum number have prices from 0 to (n-
1).
n = 1; l = 0; corresponding K shell
n = 2, l = 0, 1; corresponding L shell
n = 3; l = 0, 1, 2; appropriate skin M
n = 4; l = 0, 1, 2, 3; appropriate skin N
and so on
Sub leather prices vary is given a special name:
l = 0; fit leather sub s (s = sharp)
l = 1; fit leather sub p (p = principle)
l = 2; fit leather sub d (d = diffuse)
l = 3; fit leather sub f (f = fundamental)
3. Magnetic quantum number (m): realizing the presence of one or
several levels of energy in a sub shell. Quantum numbers
magnetic (m) has a price (-l) to price (+ l).
For:
l = 0 (sub leather s), price m = 0 (having 1 orbital)
l = 1 (p sub shell), price m = -1, O, +1 (have 3 orbitals)
l = 2 (sub skin d), price m = -2, -1, O, +1, +2 (have 5 orbitals)
l = 3 (sub kwit f), price m = -3, -2, O, +1, +2, +3 (have 7
orbital)
4. Spin quantum number (s): indicates the direction of rotation of the electron
on its axis.
In one orbital, maximum of 2 electrons can circulate and second
This electron spins through the axis in the opposite direction, and
each one is priced spin +1 / 2 or -1 / 2.
D. ELECTRON CONFIGURATION
In every atom orbitals are available, but not necessarily
all orbital is filled. How is the electron charge
these orbitals?
Completion of electrons in the orbitals satisfy some rules.
among other things:
1. Aufbau principle: electrons fill orbitals starting with
the lowest energy level and beyond.
Orbital who meet the low energy levels is 1s
followed by 2s, 2p, 3s, 3p, and on and on
made easier following diagram:
Examples of filling electrons in orbitals several elements:
Atom H: has 1 electron, configuration 1s1
Atom C: has 6 electrons, the configuration 1s2 2s2 2P2
Atom C: has 19 electrons, the configuration 1s2 2s2 2P6 3S2 3P6
4S1











2. Pauli principle: not possible in the atom there are two electrons
with the same four quantum numbers.
This means, if there are two electrons that have a number
principal quantum, and magnetic azimuth of the same, then the number
quantum spins must be opposite.
3. Principle Hund: for filling electrons in orbitals in a sub
Skin is that the electrons do not form pairs of electrons
before each filled with an electron orbital.

THERMOCHEMICAL

Thermochemical

A.      Exothermic and endothermic reactions

1.         Exothermic reaction

 In an exothermic reaction occurs heat transfer of the system to

     environment or to the reaction heat released.? In an exothermic reaction ΔH price = (-)

     Example: C (s) + O2 (g) CO2 (g) + 393.5 kJ; ΔH = -393.5 kJ

Endothermic reaction?? In endothermic reactions occur heat transfer from the environment to

     system or to the reaction heat is needed.? In endothermic reactions price ΔH = (+)

?? Example: CaCO3 (s) CaO (s) + CO2 (g) - 178.5 kJ; ΔH = +178.5 kJ

. Enthalpy changes

     Enthalpy = H = heat of reaction at constant pressure = Qp? The change in enthalpy is the energy change accompanying events

     chemical changes at a constant pressure.

    

     a. Termination of the bond requires energy (= endothermic)? Example: H2 2H - a kJ; ΔH = + AKJ

     b. Bond formation provides energy (= exothermic)? Example: H2 + 2H a kJ; ΔH =-a kJ

The term used in the enthalpy change:

Standard Enthalpy Pembuntakan (ΔHf):? ΔH animal lays to form 1 mole of compounds directly from the elements

    elements were measured at 298 K and pressure of 1 atm.

    Example: H2 (g) + 1/2 O2 (g) H20 (l); ΔHf = -285.85 kJ

Enthalpy of Decomposition:? ΔH of decomposition of 1 mole of the compound directly into its elements (= Contrary to ΔH formation).

    Example: H2O (l) H2 (g) + 1/2 O2 (g), ΔH = +285.85 kJ

Standard Enthalpy of Combustion (ΔHc):? ΔH to burn 1 mole compound with O2 from the air measured at 298 K and pressure of 1 atm.

Example: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l); ΔHc = -802 kJ

Enthalpy of reaction:? ΔH of an equation in which substances contained in the equation is expressed in units of moles and the coefficients of the equation is simple round.

Example: + 2AL 3H2SO4 Al2 (SO4) 3 + 3H2; ΔH = -1468 kJ

Enthalpy of Neutralization:? ΔH generated (always exothermic) on the neutralization of acid or alkaline reaction.

Example: NaOH (aq) + HCl (aq) NaCl (aq) + H2O (l);

             ΔH = -890.4 kJ / mol

Lavoisier-Laplace law? "The amount of heat released in the formation of one mole of substance

    elements unsurya = amount of heat required to decompose the substance into its constituent elements. "? Meaning: If the reaction is reversed the sign of the heat that is formed is also reversed from positive to negative or vice versa

    

     Example:? N2 (g) + 3H2 (g) 2NH3 (g), ΔH = - 112 kJ? 2NH3 (g) N2 (g) + 3H2 (g), ΔH = + 112 kJ

C. Determination of Enthalpy Changes and Hess's Law

1. Determination of Enthalpy Changes

     To determine the enthalpy change in a chemical reaction

     commonly used tools such as the calorimeter, thermometer and

     etc., that may be more sensitive.

     Calculation: ΔH reaction = Δ; ΔHfo products - Δ = ΔHfo reactants

2. Hess's Law

     "The amount of heat required or released in a reaction

     does not depend on the course of chemical reactions but is determined by

     initial state and the end. "

example :               

According to Hess's Law: x = y + z

D. Energy-Energy and Chemical Bonding

      A chemical reaction is a process of dissolution and formation

      ties. The process is always accompanied by energy changes. The energy

      needed to break chemical bonds, thus forming

      free radicals called the bond energy. For molecules

      complex, the energy required to break the molecule

      thus forming free atoms called atomization energy.

Atomization energy prices is the amount of the bond energy of the atoms in the molecule. For covalent molecule consisting of two atoms such as H2, 02, N2 or HI which has a bond equal to the energy of atomization energy bond energy of atomization of a compound can be determined by the help enthalpy of formation of these compounds. Mathematically it can be described by the equation.

                                                                                                                                                       

Example:

Given:

bond energy

C - H = 414.5 kJ / mole? C = C = 612.4 kJ / mol? C - C = 346.9 kJ / mol? H - H = 436.8 kJ / mol?? Asked:

ΔH reaction = C2H4 (g) + H2 (g) C2H6 (g)

Answer:

ΔH reaction = Total bond breaking energy - amount of energy

                     bond formation

                 = (4 (C-H) + (C = C) + (H-H)) - (6 (C-H) + (C-C))? = ((C = C) + (H-H)) - (2 (C-H) + (C-C))? = (612.4 + 436.8) - (2 x 414.5 + 346.9)? = - 126.7 kJ

STOICHIOMETRIC

STOICHIOMETRIC

        Stoichiometry is the branch of chemistry that studies

quantitative relation of the composition of chemical substances and reactions. Stoichiometry calculations are best done by stating the quantity of known and unknown in moles and then if need be converted into other units. Limiting reagent is the reactant present in the smallest stoichiometry amount. Reactant is limiting the amount of product that can be formed. The number of products produced in a reaction (the actual results) may be smaller than the maximum amount that may be acquired (the theoretical yield). Comparison of the two expressed as a percent of the results.

       Chemical law is a law of nature that are relevant to the field of chemistry. the concept of the

chemistry is fundamental in the law of conservation of mass, which states that no

changes in the quantity of matter during an ordinary chemical reaction. Modern physics shows

that actually happens is the conservation of energy, and that energy and mass

interconnected a concept that is important in nuclear chemistry. conservation

energy leads to the important concepts of the equilibrium,

thermodynamics, and kinetics.

       Another modern chemical law to determine the relationship between energy and transformation.

1. In equilibrium, a molecule found in the mixture is     

    determined by the

    transformation that may occur on a time scale equilibrium,  

    and has a ratio determined by the intrinsic energy of the  

    molecule. The smaller energy intrinsic, the more molecules.

2. Change one structure into another structure requires the  

    input of energy to beyond the constraints of energy, it can be  

    caused by intrinsic energy of molecules it self, or from  

    external sources will generally accelerate the change. The  

    greater the energy barrier, the slower the process of on going 

    transformation.

c. There is a structure or a transition between the hypothetical,  

    which relates to the structure in peak of the energy barrier.     

    Hammond Postulate-Leffer stated that this structure

    resembles the original product or material that has an  

    intrinsic energy closest the energy barrier. By stabilizing the 

    hypothetical structure with chemical interaction is one way  

    to achieve catalysis.

d. All chemical processes are irreversible (reversible) (law  

    reversible microscopic) although some process has a bias 

    energy, their Basically irreversible (irreversible).

A. LAWS BASIC CHEMISTRY

1. LAW OF CONSERVATION OF MASS = Lavoisier LAW

     "The mass of substances before and after the reaction is 

       fixed".

     Example:

     hydrogen + oxygen-hydrogen oxide

       (4g) (32g) (36g)

2. COMPARATIVE LAW = LEGAL PERMANENT Proust

     "Comparison of the mass of the elements in each compound 

     is fixed"

      Example:

         a. In the compound NH3: N mass: mass of H

         Ar = 1. N: 3 Ar. H

         = 1 (14): 3 (1) = 14: 3

         b. On the compound SO3: S mass: mass 0

         Ar = 1. S: 3 Ar. O

         = 1 (32): 3 (16) = 32: 48 = 2: 3

     Advantages of the law Proust:

if known mass of a compound or a mass of one of the elements that make up the compound make-masses of other elements can be determined.

    Example:

How many levels of C in 50 grams of CaCO3? (Ar: C = 12; 0 = 16; Ca = 40)

Mass C = (Ar C / Mr CaCO3) x mass of CaCO3

             = 12/100 x 50 grams = 6 grams

Levels of C = mass C / mass x 100% CaCO3

            = 6/50 x 100% = 12%

3. COMPARATIVE LAW LAW MULTIPLE = DALTON

    "When the two elements can form two or more compounds

     to the mass of one element of the same number of the mass  

    ratio of the two elements will be compared as integers and 

    simple ".

Example:

If the element nitrogen fertilized den oxygen can be formed,

NO where mass N: 0 = 14: 16 = 7: 8

NO2 which the mass N: 0 = 14: 32 = 7: 16

    For the same amount of nitrogen mass ratio of the mass of oxygen in the compound NO: NO2 = 8: 16 = 1: 2

4. GAS LAWS

    To apply the ideal gas equation: PV = nRT

    where:

    P = gas pressure (atmospheric)

    V = gas volume (liters)

     n = moles of gas

    R = universal gas constant = 0082 lt.atm / mol Kelvin

    T = absolute temperature (Kelvin)

   

   The changes of P, V and T from state 1 to state 2 with certain     

    conditions reflected by the following laws:

a. BOYLE LAW

    This law is derived from the ideal gas equation of state with

    n1 = n2 and T1 = T2; thus obtained: P1 V1 = P2 V2

    Example:

    What is the pressure of 0 5 mol O2 with a volume of 10 liters   

    when the temperature is 0.5 mol

    NH3 has a volume of 5 liters and a pressure of two 

    atmospheres?

    Answer:

    P1 V1 = P2 V2

    2. 5 = P2. 10  P2 = 1 atmosphere

b. LEGAL Gay-Lussac

    "The volume of gases that react and the volume of gas when  

    measured at the reaction temperature and pressure the same 

    in value as simple and integer ".

    So for: P1 = P2 and T1 = T2 holds: V1 / V2 = n1 / n2 

    Example:

    Calculate the mass of 10 liters of nitrogen gas (N2) if the   

    condition

    The 1 liter of hydrogen gas (H2) mass of 0.1 g.

    Given: Ar for H = 1 and N = 14

    Answer:

    V1/V2 = n1/n2 ® 10/1 = (x/28) / (0.1 / 2) ® x = 14 grams

    So mass = 14 grams of nitrogen gas.

c. BOYLE LAW-Gay Lussac

    This law is an extension of the previous law and lowered

    the state n = n2 price in order to obtain the equation:

    P1. V1 / T1 = P2. V2 / T2

d. Avogadro's law

    "At the same temperature and pressure, the volume of gases  

    the same contains the same number of moles. "

    Example:

Hydrogen    +      Chlorine      à hydrogen chloride

       n molecules         n molecule             2n molecular

divided by n

       1 molecule         +               1 molecul à        2 molecules

   Hydrogen                            chlorine               hydrogen chloride

Example: What is the volume of gas at a temperature of 29 grams of C4H10 and constant pressure, where 35 liters of oxygen weighs 40 grams   (Mr. C4 H10 = 58; Ar O = 16)

Answer: Mol C4H10 = 29/54 = 0.5 mol

                Mol O2 = 40/32 = 1.25 mol

               1/2 mol C4H10 = 0.5 / 1.25 x 35 = 14 liters

B. ATOM MASS AND MASS FORMULA

     

    1. Relative Atomic Mass (Ar)

          

               is the ratio between the mass of one atom with 1/12 the   

     mass. 1 atom of carbon 12.

           Dalton recognized that it is important to determine the mass of each atom as mass varies for each type of atom. Atom is very small so it is not possible to determine the mass of a single atom. So he focuses on the relative masses and create a table atomic mass (Figure 1.3) for the first time in human history. In the table, the mass of the lightest element, hydrogen adoption as a standard one (H = 1). Atomic mass is a relative value, meaning that a dimensionless ratio. Although
several different atomic masses with modern values​​, most of the proposed values ​​in the range of compatibility with the current value. This shows that the idea and the experiment right.

        Then the Swedish chemist Jons Jakob Berzelius Baron (1779-1848) to determine the mass of the oxygen atom as the standard (O = 100). Because Berzelius get this value based on the analysis of oxide, it has a clear reason to choose oxygen as standard. However, the standard hydrogen is clearly superior in terms of simplicity. Now, after much discussion and modification, carbon standard is used. In this method, the mass of 12C carbon with 6 protons and 6 neutrons is defined as 12.0000. Atomic mass is the mass of an atom relative to this standard. Although carbon has been declared as standard, this can actually be considered as a standard hydrogen is modified.

2. Relative Molecular Mass (Mr)

             is the ratio between the mass of 1 molecule compounds

    1/12 the mass of one atom of carbon 12.

    Relative molecular mass (Mr) of a compound is the sum

    atomic mass of constituent elements.

Example:

    If Ar for X = 10 and Y = 50 what Mr. compound X2Y4?

Answer:

    Mr X2Y4 = 2 x Ar. X + 4 x Ar. Y = (2 x 10) + (4 x 50) = 220

C. CONCEPT MOL

      1 mole is the amount of the chemical unit numbers of the atoms or molecules of Avogadro's number and mass = Mr compound.

If Avogadro's number = L then:

                                                    L = 6.023 x 1023

1 mole of atoms = L atoms, mass = Ar atom.

1 mole of molecules = L = Mr fruits molecular mass of the molecule.

The mass of one mole of a substance is called the molar mass of the substance

Example:

How many molecules are present in 20 grams of NaOH?

Answer:

Mr NaOH = 23 + 16 + 1 = 40

mol NaOH = mass / Mr = 20/40 = 0.5 mol

The number of molecules of NaOH = 0.5 L

                                      = 0.5 x 6023 x 1023

                                      = 3.01 x 1023 molecules.

D. EQUAL REACTION

NATURE HAVE EQUAL REACTION

1. Types of elements before and after the reaction is always the
     same

2. The number of each atom before and after the reaction

    always the same

3. Comparison of the reaction coefficient expressed mole ratio

    (Specifically in the form of gas ratio coefficient is also states  
     as long as the volume ratio den temperature pressure is the  
     same)

    Example: Find the coefficient of reaction

                  HNO3 (aq) + H2S (g) ® NO (g) + S (s) + H2O (l)

    The easiest way to determine the coefficient of the reaction is

    by letting the coefficient of each a, b, c, d and e

    so:

         a HNO3 + H2S b c d S + NO + e H2O

         Based on the above reaction

         N atoms: a = c (before and after the reaction)

         atom O: 3a = c + e 3a = a + e e = 2a

         H atoms: a + 2b = 2e = 2 (2a) = 4a; 2b = 3a, b = 3/2 a

         atom S: b = d = 3/2 a

         So that we resolved to take any price eg a = 2

         means: b = d = 3, and e = 4 so the equation:

           2 HNO3 + 3 H2S + 3 S 2 NO + 4 H2O

Chemical Reaction

Chemical Reactions

by Anthony Carpi, Ph.D.

In the late 1890s, the Scottish chemist Sir William Ramsay discovered the elements helium, neon, argon, krypton, and xenon. These elements, along with radon, were placed in group VIIIA of the periodic table and nicknamed inert (or noble) gases because of their tendency not to react with other elements (see our Periodic Table page). The tendency of the noble gases to not react with other elements has to do with their electron configurations. All of the noble gases have full valence shells; this configuration is a stable configuration and one that other elements try to achieve by reacting together. In other words, the reason atoms react with each other is to reach a state in which their valence shell is filled.
Let's look at the reaction of sodium with chlorine. In their atomic states, sodium has one valence electron and chlorine has seven.

Sodium	Chlorine

Chlorine, with seven valence electrons, needs one additional electron to complete its valence shell with eight electrons. Sodium is a little bit trickier. At first it appears that sodium needs seven additional electrons to complete its valence shell. But this would give sodium a -7 electrical charge and make it highly imbalanced in terms of the number of electrons (negative charges) relative to the number of protons (positive charges). As it turns out, it is much easier for sodium to give up its one valence electron and become a +1 ion. In doing so, the sodium atom empties its third electron shell and now the outermost shell that contains electrons, its second shell, is filled - agreeing with our earlier statement that atoms react because they are trying to fill their valence shell.

Sodium Chloride

This trait, the tendency to lose electrons when entering into chemical reactions, is common to all metals. The number of electrons metal atoms will lose (and the charge they will take on) is equal to the number of electrons in the atom's valence shell. For all of the elements in group A of the periodic table, the number of valence electrons is equal to the group number (see our Periodic Table page).
Nonmetals, by comparison, tend to gain electrons (or share them) to complete their valence shells. For all of the nonmetals, except hydrogen and helium, their valence shell is complete with eight electrons. Therefore, nonmetals gain electrons corresponding to the formula = 8 - (group #). Chlorine, in group 7, will gain 8 - 7 = 1 electron and form a -1 ion.
Hydrogen and helium only have electrons in their first electron shell.  The capacity of this shell is two.  Thus helium, with two electrons, already has a full valence shell and falls into the group of elements that tend not to react with others, the noble gases.  Hydrogen, with one valence electron, will gain one electron when forming a negative ion.  However, hydrogen and the elements on the periodic table labeled metalloids, can actually form either positive or negative ions corresponding to the number of valence electrons they have.  Thus hydrogen will form a +1 ion when it loses its one electron and a -1 ion when it gains one electron.

Reaction energy

All chemical reactions are accompanied by a change in energy. Some reactions release energy to their surroundings (usually in the form of heat) and are called exothermic. For example, sodium and chlorine react so violently that flames can be seen as the exothermic reaction gives off heat. On the other hand, some reactions need to absorb heat from their surroundings to proceed. These reactions are called endothermic. A good example of an endothermic reaction is that which takes place inside of an instant '"cold pack." Commercial cold packs usually consist of two compounds - urea and ammonium chloride in separate containers within a plastic bag. When the bag is bent and the inside containers are broken, the two compounds mix together and begin to react. Because the reaction is endothermic, it absorbs heat from the surrounding environment and the bag gets cold.
Reactions that proceed immediately when two substances are mixed together (such as the reaction of sodium with chlorine or urea with ammonium chloride) are called spontaneous reactions. Not all reactions proceed spontaneously. For example, think of a match. When you strike a match you are causing a reaction between the chemicals in the match head and oxygen in the air. The match won't light spontaneously, though. You first need to input energy, which is called the activation energy of the reaction. In the case of the match, you supply activation energy in the form of heat by striking the match on the matchbook; after the activation energy is absorbed and the reaction begins, the reaction continues until you either extinguish the flame or you run out of material to react.

Chemical reaction

From Wikipedia, the free encyclopedia

A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.

Video demonstrating a chemical reaction.

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.^[1] Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds between atoms, and can often be described by a chemical equation.
The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions.
Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration, and rapid reactions are often described as spontaneous, requiring no input of extra energy other than thermal energy. Non-spontaneous reactions run so slowly that they are considered to require the input of some type of additional energy (such as extra heat, light or electricity) in order to proceed to completion (chemical equilibrium) at human time scales.
Different chemical reactions are used in combinations during in chemical synthesis in order to obtain a desired product. In biochemistry, a similar series of chemical reactions form metabolic pathways. These reactions are often catalyzed by protein enzymes. These enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions may be performed at the temperatures and concentrations present within a cell.
The general concept of a chemical reaction has been extended to non-chemical reactions between entities smaller than atoms, including nuclear reactions, radioactive decays, and reactions between elementary particles as described by quantum field theory.

A chemical reaction is a process in which one set of chemical substances (reactants) is converted into another (products). It involves making and breaking chemical bonds and the rearrangement of atoms. Chemical reactions are represented by balanced chemical equations, with chemical formulas symbolizing reactants and products. For specific chemical reactants, two questions may be posed about a possible chemical reaction. First, will a reaction occur? Second, what are the possible products if a reaction occurs? This

Sulfur reacting to heat.

entry will focus only on the second question. The most reliable answer is obtained by conducting an experiment—mixing the reactants and then isolating and identifying the products. We can also use periodicity, since elements within the same group in the Periodic Table undergo similar reactions. Finally, we can use rules to help predict the products of reactions, based on the classification of inorganic chemical reactions into four general categories: combination, decomposition, single-displacement, and double-displacement reactions.
Reactions may also be classified according to whether the oxidation number of one or more elements changes. Those reactions in which a change in oxidation number occurs are called oxidation–reduction reactions . One element increases its oxidation number (is oxidized), while the other decreases its oxidation number (is reduced).

characteristics of chemical reactions1. Colour Change Happen
In a chemical reaction, reactants are converted into products. Changes may occur due to the termination of the bonds of the reactants and the formation antaratom ties bru that make up the product. Energy required to break the tie. To form a new bond, released some energy. Thus, the chemical reaction energy changes.
Chemical reactions that produce energy in the form of heat is called exothermic reactions. Reactions that absorb heat energy called endothermic reactions.
Example: Fire can warm up a cold and when hot breath in the body due to exercise so that the body becomes cold expelled.
trial
2. Temperature changes occur
In a chemical reaction, reactants are converted into products. Changes may occur due to the termination of ties antaratom reagents and formation of new bonds that make up the product. Energy required to break the tie.
Chemical reactions that produce energy in the form of heat is called exothermic reaction, while the reaction absorbs heat energy called endothermic reactions.
A chemical reaction occurs in a space that we call dbngan system, places outside the system is called the surroundings.
In exothermic reactions, heat transfer occurs from sisitem to the environment.
In endothermic reactions occur transfer heat energy from the environment to the system.
trial
3. Sediment formation occurs
When two solutions react in a test tube, sometimes forming an insoluble sneyawa, solid, and separated from the solution. The solid is called the precipitate (precipitate)
trial
4. Gas Formation occurs
Simply put, the chemical reaction created a gas which indicated the presence of bubbles in solution reacted. The gas can be determined from the typical smell, like sour sulfide (H2S) and ammonia (NH3), which stinks.