LESSON PLAN (RPP) Of Entalphy On Curriculum 2013

LESSON PLAN (RPP)

Education units Subjects Class / semesters Subject matter Time Allocation

: High School : Chemistry : X / I : Reaction enthalpy changes : 4 hours / week

I.         CORE COMPETENCE

KI 1 KI 2 KI 3 KI 4

:Appreciate and practice the teachings of their religion : Appreciate and practice honest behavior, discipline, responsibility, caring (gotong royong, cooperation, tolerance, peace), polite, responsive and pro-active and displayed as part of the solution to various problems in interacting effectively with the social and natural environment as well as in placing itself as a reflection of the nation in the association world. : Understand, implement, analyze the factual knowledge, conceptual, procedural based flavor ingintahunya about science, technology, art, culture, and humanities with insights into humanity, nation, state, and civilization-related causes of phenomena and events, as well as applying procedural knowledge in the field of study specific according to their talents and interests to solve the problem, : Processing, reasoning, and menyaji in the realm of the concrete and the abstract realm associated with the development of learned in school independently, and able to use the method according to the rules of science.

II.      BASIC COMPETENCIES

1.1. 1.2 1.3. 1.4. 1.5.

Recognizing the regularity of hydrocarbon properties, thermochemical, lajureaksi, chemical equilibrium, solutions and colloids as a manifestation of the greatness of Almighty God and the knowledge of their regularity as a result of human creative thinking tentative truth. Grateful for Indonesia's natural wealth in the form of petroleum, coal and natural gas as well as various other mineral as a gift of God Almighty and can be used for the welfare of the people of Indonesia Shows the behavior of scientific (curious, disciplined, honest, objective, open, able to distinguish between fact and opinion, tenacious, thorough, responsible, critical, creative, innovative, democratic, communicative) in designing and conducting experiments and discussions are embodied in everyday attitude. Menunjukkanperilaku cooperation, courtesy, tolerance, cintadamai and care for the environment and saving in the use of natural resources. Exhibit behaviors responsive and pro-active as well as wise as a manifestation of the ability to solve problems and make decisions Designing, conducting, and concluding, and presents the results of experimental determination DH reaction.

III.   INDICATOR

1          Recognizing the regularity of hydrocarbon properties, thermochemical, lajureaksi, chemical equilibrium, solutions and colloids as a manifestation of the greatness of Almighty God and the knowledge of their regularity as a result of human creative thinking tentative truth.

2          Grateful for Indonesia's natural wealth in the form of petroleum, coal and natural gas as well as various other mineral as a gift of God Almighty and can be used for the welfare of the people of Indonesia

3          Shows scientific behavior (curiosity, discipline, honest, objective, open, able to distinguish between fact and opinion, tenacious, thorough, responsible, critical, creative.

4          DeterminepriceDH  neutralization between NaOH solution and a solution of HCl,

5          Compile a report on the experiment is DH neutralization between NaOH solution and a solution of HCl

IV.   LEARNING OBJECTIVES

1          students are able toconcluded priceDH  neutralization between NaOH solution and a solution of HCl,

2          students are able to students can prepare reports experimental results DH neutralization between NaOH solution and a solution of HCl,

V.      TEACHING MATERIALS

Determining ΔH A Reaction With Calorimeter

VI.   LEARNING METHODS

1.    Method            : Discussions, lectures, and FAQ.

2.    Model              : Cooperative, CTL

VII. EQUIPMENT / MEDIA / MATERIALS

1.    Media 2.    material

: Power point : Handbook of Chemistry vol 1 and supplementary relevant

VIII.       STEP ACTIVITY

Details of activities	Time
PRELIMINARY 1.     Students answered greeting teachers, pray, and conditioning themselves ready to learn. 2.     Students and teachers asked responsibilities pertaining to the universe. 3.     Students listened to an explanation of the purpose of learning and mastering the benefits of learning materials. 4.    Students listened scope of learning materials are delivered properly.	20 minutes
CORE ACTIVITIES Observe (Observing) ·       Gather information by reading / hearing / watching / systems and the environment, changes in temperature, the heat produced in the combustion of fuel, and the impact of incomplete combustion of various fuels Ask (Questioning) ·       Asking questions related to:   exothermic and endothermic reactions in daily life, how to determine the reaction enthalpy change Gather data (Eksperimenting) ·     Discuss the definition of the system and the environment ·     Discussing various changes in enthalpy ·     Designing and presenting experimental design      - Determination of the enthalpy changes calorimeter -   Determination Heat Fuel Combustion  ·     Conducting experiments, determine the enthalpy change of the calorimeter and determining the heat of combustion of fuel ·     Observe and record the results of the experiment associate (Associating) ·     Analyze data to create charts and diagrams cycle level ·     Examines the data to determine the price change in enthalpy (principle Black) Communicating (Communicating) ·     Report the results of the experiment using proper grammar. ·     Presenting the results of the experiment using proper grammar.	70 Minutes
COVER ·     Students conclude the materials that have been studied ·     The student reflects mastery of the material that has been studied by making notes mastery of the material. ·     Students do the evaluation.	10 minutes

IX.   ASSESSMENT

1.      Mechanisms and procedures

Assessment carried out of the process and results. Assessment process carried out through the activity (active discussions, communicate and ask). While the results of the assessment is done through a written test.

2.      Example Instrument (Attached)

Note:

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Jambi, August 2017

Knowing Head of SMA Negeri 1 newyork Drs. H. masagitusih B, M.Pd NIP. 999999999999999999

Subject teachers karlina, S.Pd

Predicting Product Of The Reactions

In determining the direction of a chemical reaction we must rely on an understanding based on a number of factors, and contributions that are not always easy to assess. Although the assessment is prone to error, but it is usually reliable where it seems reasonable to try, and that is certainly to answer ignorance.

In predicting chemical reactions there are several known factors such as, if the free energy of a reaction is known, then there is no problem predicting a chemical reaction. Then if only enthalpy changes are known, then predictions usually apply to room temperature but are more or less reliable as well for higher temperatures. If the reaction occurring in the solution and the oxidation potential of the involved compound is known then the prediction is relatively simple, and this oxidation potential buys a rough guide for possible reactions in the absence of a solvent. If the equilibrium constant is known, relating to ΔG0 = - RH in K gives us a change of free energy. But information like this is still lacking, so we must rely on our understanding of the preceding principles.

For chemical reactions at room temperature the expected entropy changes are not so great that the relative strength of the reactants and the products produced will guide the course of the reaction. Here are the rules that may be useful and will be used.

The reaction tends to occur where the bonds of the orbitals and some of the electrons are available and allow for attractive tensile interactions between atoms.

There is the possibility of electrons to be divided, and it always happens with energy changes. Therefore we can predict with certainty that all atoms that have empty or full orbitals will join the ability of the atoms under the applicable conditions whether produced by the same or different elements. The only elements of atomic forests do not join in ordinary circumstances are those that do not contain atoms of low external energy ie: "inert" elements or helium groups. Even this, when the circumstances are created, then through the influence of highly electronegative elements such as fluorine can be united by chemical bonds.

When that possibility exists, the tendency of atoms to form strong bonds may be formed, if at room temperature or at higher temperatures, then on the outcome there is little influence from the circumstances. In predicting reactions at ordinary temperatures, we can consider the preceding principles or bond strength and seek to decide whether the total bond strength will be greater in the reactants or products. On this basis we can often make prediction rules for definite possibilities or on reactions.

The types of reactions that are predicted by this kind are most only some of them as follows:

(1) Synthesis - a direct combination of elements or compounds,

(2) Substitution - transfer of one element or compound, from excessive complex combinations with other elements or compounds, and

(3) Metathesis - double decomposition, or exchange partner.

Synthesis

Almost all the different elements in electronegativity, the bond between two different elements of eletronegaivitas almost always polar. As already indicated, that polar tends to be stronger than nonpolar bonds. The bonds between two different elements of their electonegativity tend to show the strength of the average bond or bond on the free element. The heat of formation in larger compounds of binary compounds is largely negative (exothermic), and generally it is better to have different electronegativity and resultant bond polarities.

Part of the lure of chemistry is that things don’t always work out the way you expect. You plan a reaction, anticipate the products and, quite often, the results astound you! The exercise, then, is trying to figure out what was formed, why, and whether your observation leads to other useful generalizations. The first step in this process of discovery is anticipating or predicting the products which are likely to be formed in a given chemical reaction. The guidelines we describe here will accurately predict the products of most classes of simple chemical reactions. As your experience in chemistry grows, however, you will begin to appreciate the unexpected!

In simple synthesis reactions involving reaction of elements, such as aluminum metal reacting with chlorine gas, the product will be a simple compound containing both elements. In this case, it is easiest to consider the common charges that the elements adopt as ions and build your product accordingly. Aluminum is a Group III element and will typically form a +3 ion. Chlorine, being Group VII, will accept one electron and form a monoanion. Putting these predictions together, the product is likely to be AlCl3. In fact, if aluminum metal and chlorine gas are allowed to react, solid AlCl3 is the predominant product.

2 Al (s) + 3 Cl2 (g) → 2 AlCl3 (s)

The synthesis reaction involving the non-metals hydrogen gas and bromine can be approached similarly. The product will contain both elements. Hydrogen, Group I, has one valence electron and will form one covalent bond. Bromine, Group VII, has seven valence electrons and will form one covalent bond. The likely product is therefore HBr, with one covalent bond between the hydrogen and the bromine.

H2 (g) + Br2 (g) < → 2 HBr (g)

For a single-replacement reaction, recall that (in general) metals will replace metals and non-metals will replace non-metals. For the reaction between lead(IV) chloride and fluorine gas, the fluorine will replace the chlorine, leading to a compound between lead and fluorine and the production of elemental chlorine. The lead can be viewed as a “spectator” in the reaction and the product is likely to be lead(IV) fluoride. The complete equation is shown below.

PbCl4 (s) + 2 F2 (g) → PbF4 (s) + 2 Cl2 (g)

In single-replacement reactions in which metals (or carbon or hydrogen) are expected to replace metals, first you should check the activity series to see if any reaction is anticipated. Remember that metals can only replace metals that are less active than themselves (to the right in the Table). If the reaction is predicted to occur, use the same general guidelines that we used above. For example, solid iron reacting with aqueous sulfuric acid (H2SO4). In this reaction the question is whether iron will displace hydrogen and form hydrogen gas. Consulting the activity series, we see that hydrogen is to the right of iron, meaning that the reaction is expected to occur. Next, we reason that iron will replace hydrogen, leading to the formation of iron sulfate, where the sulfate is the “spectator” ion. The formation of hydrogen gas requires a change in oxidation number in the hydrogen of +1 to zero. Two hydrogen atoms must therefore be reduced (a decrease in oxidation number) and the two electrons required for the reduction must come from the iron. The charge on the iron is therefore most likely to be +2 (it starts off at zero and donates two electrons to the hydrogens). The final product is therefore most likely iron(II) sulfate. The complete equation is shown below.

Fe (s) + H2SO4 (aq) → FeSO4 (aq) + H2 (g)

Decomposition reactions are the most difficult to predict, but there are some general trends that are useful. For example, most metal carbonates will decompose on heating to yield the metal oxide and carbon dioxide.

NiCO3 (s) → NiO (s) + CO2 (g)

Metal hydrogen carbonates also decompose on heating to give the metal carbonate, carbon dioxide and water.

2 NaHCO3 (s) → Na2CO3 (s) + H2O (g) + CO2 (g)

Finally, many oxygen-containing compounds will decompose on heating to yield oxygen gas and “other compounds”. Identifying these compounds and building an understanding of why and how they are formed is one of the challenges of chemistry. Some examples:

H2O2 (aq) → O2 (g) + H2O (l)

2 HgO (s) → O2 (g) + 2 Hg (l)

2 KClO3 (s) → 3 O2 (g) + 2 KCl (s)

The potential products in double-replacement reactions are simple to predict; the anions and cations simply exchange. Remember, however, that one of the products must precipitate, otherwise no chemical reaction has occurred. For the reaction between lead(II) nitrate and potassium iodide, the products are predicted to be lead(II) iodide and potassium nitrate. No redox occurs, and the product, lead iodide, precipitates from the solution as a bright yellow solid. The question of how do you predict this type of solubility trend is addressed in the next section.

Pb(NO3)2 (aq) + 2 KI(aq)< → PbI2 (s) + 2 KNO3 (aq)

Using English to Report

CHEMICAL REPORT

"Redox Reaction"

CHAPTER I

PRELIMINARY

A. Purpose:

In this activity will be studied spontaneous redox reactions and not spontaneous

B. Platform Theory:

Reduction is the acceptance of electrons or decreases in oxidation numbers, whereas oxidation is the release of electrons or an increase in the oxidation number. The redox reaction is a combination of the simultaneous reduction and oxidation reactions. There is no electron discharge event (oxidation reaction) without an electron capture event (reduction reaction). Redox reactions may be either spontaneous or spontaneous.

The spontaneity of a redox reaction can be determined using a voltaic series. The order of the metals in the volt series is:

K-Ba-Ca-Na-Mg-Al-Mn-Zn-Cr-Fe-Cd-Co-Ni-Sn-Pb- (H2) -Sb-Bi-Cu-Hg-Ag-Pt-Au

The metals next to k2H2 are active metals (strong reducing agents) while the metals on the right H2 are less active (weak reductors). The more to the left the reductor properties are getting weaker and the oxidizing properties get stronger. The metals in the voltaic series can reduce the elements of the dikanannya but not able to reduce the elements on the left. If a metal can reduce the elements to the right, the reaction is spontaneous. Conversely, if not able to reduce the elements on the right reaction is not spontaneous.

Chemical reactions that take place spontaneously, characterized by the characteristics of the resulting sediment, bubbles, changes in color, and changes in temperature.

CHAPTER II

OBSERVATION METHODS

A. Draft Practicum:

In this lab, the author designed the lab using the literature and experimental method. The literature review is conducted so that the authors obtain theories as a reference for the lab. Authors do literature review activities by surfing the internet.

To strengthen the existing theories, the authors conduct experimental model experiments to prove the author's hypothesis in accordance with theories obtained by the author.

C. Practical Variables:

A variable is something that is measured in the writing of a practicum report. The variables considered in the writing of a report of this practice is spontaneous and not spontaneous reaction.

D. Data Collection Technique:

            As a reference to create practical reports, the author looks for various data related to the title of various books and internet. The literature review is used as a reference for obtaining existing data and theories. The author studied and poured existing sources into the manufacture of practical reports.

E. Work Steps

Tools and materials

Size / Unit

amount

The reaction tube / rack

Drop pipette

ZnSO4 solution

CuSO4 solution

HCl solution

Zinc metal plate / Zn

Copper metal plate / Cu

Sandpaper

-

-

1 m

1 m

1 m

0.5 x 1 cm

0.5 x 1 cm

-

4/1

3

5 mL

5 mL

10 mL

2 pieces

2 pieces

Sufficiently

  

B. Ways of working:

1. Fill the glass with water approximately three-quarters of a piece, add 10 drops of phenolphthalein solution

2. Squeeze with metal pliers and lift sodium metal from a storage bottle. Using paper filter any kerosene from the metal surface. Observe the metal's appearance, then irislah the metal with a dry knife, observe the surface of the slice

3. Cut the sodium metal as big as green beans. Using an iron pliers, wrap metal sodium tightly and then insert the piece of metal into a water-filled glass of phenol ftalein, immediately cover the beaker with a solder dish

4. Record all necessary observations

CHAPTER III

RESULTS OF OBSERVATIONS AND DISCUSSIONS

A. Observation Tables:

Tube 1

Tubes 2

Tube 3

Tubes 4

Solution filled

CuSO4

ZnSO4

HCl

HCl

Color of solution

Blue

Snappy

Clear

Clear

Added metal

Zinc

Copper

Zinc

Copper

Changes after metal enhancement

The metal is black and there are bubbles

No reaction

There are bubbles

The metal becomes clean

B. Analysis and Discussion:

In this experiment, the CuSO4 solution released the characteristics of spontaneous reactions as described in the theoretical basis above. Once observed, it turns out that a solution of CuSO4 is inserted in the zinc metal plate, releasing small bubbles around the zinc plate. Zinc plates are also slowly undergoing corrosion. If the experiment is carried out longer, the zinc plate will be destroyed and become a precipitate in CuSO4 solution. This negates that the reaction occurring in CuSO4 solution is a spontaneous reaction.

Meanwhile, in the ZnSO4 solution which is inserted in the copper plate, there is no change in either the slab or the ZnSO4 solution. This indicates that the reaction occurring in ZnSO4 solution is a meaningless spontaneous reaction, in which the solution requires external energy for reaction.

HCl solution secretes spontaneous reaction features. Once observed, the HCl solution in which is inserted a zinc metal plate, removing small bubbles around the zinc plates

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Using English to Calculate

Stoichiometry is the basic chemical calculation that states quantitative relation of chemical formulas and chemical equations. Here are the materials you need to know to understand, from the concept of moles and molar masses, empirical formulas and molecular formulas, basic stoichiometry of solutions and ideal gases, and the writing and equalization of reactions, with examples of problems and discussions. In chemistry, chemical reactions are frequently written as an equation, using chemical symbols. The reactants are displayed on the left side of the equation and the products are shown on the right, with the separation of either a single or double arrow that signifies the direction of the reaction. The significance of single and double arrow is important when discussing solubility constants, but we will not go into detail about it in this module. To balance an equation, it is necessary that there are the same number of atoms on the left side of the equation as the right. One can do this by raising the coefficients.

Reactants to Products

A chemical equation is like a recipe for a reaction so it displays all the ingredients or terms of a chemical reaction. It includes the elements, molecules, or ions in the reactants and in the products as well as their states, and the proportion for how much of each particle is create relative to one another, through the stoichiometric coefficient. The following equation demonstrates the typical format of a chemical equation

2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g)

In the above equation, the elements present in the reaction are represented by their chemical symbols. Based on the Law of Conservation of Mass, which states that matter is neither created nor destroyed in a chemical reaction, every chemical reaction has the same elements in its reactants and products, though the elements they are paired up with often change in a reaction. In this reaction, sodium (NaNa), hydrogen (HH), and chloride (ClCl) are the elements present in both reactants, so based on the law of conservation of mass, they are also present on the product side of the equations. Displaying each element is important when using the chemical equation to convert between elements.

Stoichiometric Coefficients

In a balanced reaction, both sides of the equation have the same number of elements. The stoichiometric coefficient is the number written in front of atoms, ion and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation. Though the stoichiometric coefficients can be fractions, whole numbers are frequently used and often preferred. This stoichiometric coefficients are useful since they establish the mole ratio between reactants and products. In the balanced equation:

2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g)

we can determine that 2 moles of HClHCl will react with 2 moles of Na(s)Na(s) to form 2 moles of NaCl(aq)NaCl(aq) and 1 mole of H2(g)H2(g). If we know how many moles of NaNa we start out with, we can use the ratio of 2 moles of NaClNaCl to 2 moles of Na to determine how many moles of NaClNaCl were produced or we can use the ration of 1 mole of H2H2 to 2 moles of NaNa to convert to NaClNaCl. This is known as the coefficient factor. The balanced equation makes it possible to convert information about one reactant or product to quantitative data about another element. Understanding this is essential to solving stoichiometric problems.

Molar and Molar Mass Concepts (})

In SI systems, one mole is defined as the sum of the material composed of entities (atoms, molecules, or other particles) a sum of the atoms in 12 grams of carbon-12. The value of the number of atoms is 6.022 × 1023 called the Avogadro number, NA.

Stoichiometry Reaction

In chemical reactions, the amount of reacting reactants is sometimes incompatible with the stoichiometric amount of the reaction (not in accordance with the coefficient ratio of the equivalent equation). Therefore, there will be reactants that have reacted first compared to other reactants. The reactants that remain after reacting are called excess reagents. The out-of-date reactant is called a limiting reagent. After the barrier reagents are exhausted, no more reaction products are formed. Thus, the number of limiting reagents determines the amount of product produced.

Empirical Formulas and Molecular Formulas

The empirical formula is the simplest integer ratio of the number of moles of each element in a compound. The molecular formula represents the true number of moles of each element in 1 mole of the compound. The molecular formula may be identical to the empirical formula or an integer multiple of the empirical formula. For example, phosphoric acid (H3PO4) has a molecular formula and an identical empirical formula. Glucose has a molecular formula C6H12O6 which is a folding of 6 times its empirical formula, CH2O.

Molecular formula ≡ (empirical formula) n

 Molecular formula = n ×} empirical formula, n = 1, 2, 3, ...

Basic Stoichiometric Solution

The term "concentration" of the solution expresses the amount of solute dissolved in a certain amount of solvent or a certain amount of solution. The concentration of the solution can be expressed in molarity. Molarity (M) is defined as the number of moles of solute per liter of solution.

Variation in Stoichiometric Equations

Almost every quantitative relationship can be converted into a ratio that can be useful in data analysis.

Density

Density (ρρ) is calculated as mass/volume. This ratio can be useful in determining the volume of a solution, given the mass or useful in finding the mass given the volume. In the latter case, the inverse relationship would be used.

Volume x (Mass/Volume) = Mass

Mass x (Volume/Mass) = Volume

Percent Mass

Percents establish a relationship as well. A percent mass states how many grams of a mixture are of a certain element or molecule. The percent X% states that of every 100 grams of a mixture, X grams are of the stated element or compound. This is useful in determining mass of a desired substance in a molecule.

EXAMPLE :

1) What is the molar mass of H2O?

SOLUTIONMolar mass=2×(1.00794g/mol)+1×(15.9994g/mol)=18.01528g/molMolar mass=2×(1.00794g/mol)+1×(15.9994g/mol)=18.01528g/mol

Using molar mass and coefficient factors, it is possible to convert mass of reactants to mass of products or vice versa.

2) A substance is 5% carbon by mass. If the total mass of the substance is 10 grams, what is the mass of carbon in the sample? How many moles of carbon are there?

SOLUTION

10 g sample x (5 g carbon/100 g sample) = 0.5 g carbon

0.5g carbon x (1 mol carbon/12.011g carbon) = 0.0416 mol carbon

3) How much 5 M stock solution is needed to prepare 100 mL of 2 M solution?

SOLUTION

100 mL of dilute solution (1 L/1000 mL)(2 mol/1L solution)(1 L stock solution/5 mol solution)(1000 ml stock solution/1L stock solution) = 40 mL stock solution.

Using English to give 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.  

1. Light is given off: Potential energy in valance electrons is released in the form of light.

2.Gas is given off: Indicates an increase in kinetic energy of the atom (compound) as it is changed to a gas.

3. Temperature change: Exothermic is an increase in the speed of the molecules (heat). Exothermic is the taking in of energy.

4. Color change: the increase or decrease of potential energy stored in new bonds.

5. Precipitate formed: increase or decrease of potential energy in new bonds formed.

6. 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.