14 SECTION 2 Chemical Formulas And Equations
NameClassCHAPTER 14DateChemical ReactionsSECTION2 Chemical Formulas and EquationsNational ScienceEducation StandardsBEFORE YOU READAfter you read this section, you should be able to answerthese questions:PS 1b What are chemical formulas? What are chemical equations? How do you balance a chemical equation?What Is a Chemical Formula?We use letters to form words. We put words together toform sentences. In the same way, scientists use symbols toform chemical formulas that describe different substances.They put chemical formulas together to show how chemicalreactions happen.Remember that substances are formed from differentelements. Each element has its own chemical symbol.You can find the symbol for an element in the periodictable. Scientists combine the symbols for different elements when they write chemical formulas. A chemicalformula shows which elements are found in a substance.It also shows how many atoms of each element are foundin a molecule of the substance.In order to learn how chemical formulas work, let’s lookat an example. The chemical formula for water is H2O. Thisformula means that a molecule of water is made of twohydrogen (H) atoms and one oxygen (O) atom.The small 2 in the formula is a subscript. A subscript isa number that tells you how many atoms of an element arein a molecule. Subscripts are always written below and tothe right of the symbol for an element. No subscript with anelement’s chemical symbol means the substance has only oneatom of the element.WaterOxygenGlucoseH2OO2C6H12O6Water A molecule ofOxygen A moleculewater contains 2 hydrogen of oxygen is made of(H) atoms and 1 oxygen2 oxygen (O) atoms.(O) atom.Glucose A molecule ofglucose cotains 6 carbon (C)atoms, 12 hydrogen (H) atomsand 6 oxygen (O) atoms.STUDY TIPAsk Questions As you readthis section, make a list ofquestions that you have. Talkabout your questions with asmall group. When you figureout the answers to yourquestions, write them in yournotebook.READING CHECK1. Identify What are twothings that are shown by achemical formula?Math Focus2. Calculate How manyoxygen atoms are in threemolecules of water?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook247Chemical Reactions
NameSECTION 2ClassDateChemical Formulas and Equations continuedFORMULAS FOR COVALENT COMPOUNDSCritical Thinking3. Apply Concepts Writethe formula for the covalentcompound whose name isphosphorus trichloride.In many cases, the name of a covalent compound tellsyou how to write its chemical formula. This is becausethe names of many covalent compounds use prefixes.Prefixes represent numbers. For example, the prefix dimeans “two.” The prefixes tell you how many atoms of anelement are found in a substance. The table below showsthe meanings of different on dioxideDinitrogen monoxideCO2N2OThe absence of a prefixindicates one carbon atom.The prefix di- indicatestwo oxygen atoms.Math Focus4. Identify What is thecharge on the Fe ion in theionic compound FeCl3? Hint:find the charge of a chlorideion.The prefix di- indicatestwo nitrogen atoms.The prefix mono- indicatesone oxygen atom.FORMULAS FOR IONIC COMPOUNDSIf the name of a compound contains the name of ametal and a nonmetal, the compound is ionic. To writethe name of an ionic compound, make sure the compound’s charge is 0. Therefore, the formula must havesubscripts that cause the charges of the ions to cancel.The figure below shows some examples of how to nameionic compounds.Sodium chlorideMagnesium chlorideNaClMgCl2A sodium ion hasa 1 charge.A chloride ion hasa 1– charge.One sodium ion and onechloride ion have an overallcharge of (1 ) (1–) 0.A magnesium ion hasa 2 charge.A chloride ion hasa 1– charge.One magnesium ion and twochloride ions have an overallcharge of (2 ) 2(1–) 0.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook248Chemical Reactions
NameSECTION 2ClassDateChemical Formulas and Equations continuedHow Are Chemical Formulas Used to WriteChemical Equations?Scientists use chemical equations to describe reactions. A chemical equation uses chemical symbolsand formulas as a short way to show what happens in achemical reaction. A chemical equation shows that atomsare only rearranged in a chemical reaction. No atoms aregained or lost in a chemical reaction.The starting materials in a chemical reaction are thereactants. The substances that form during the reaction are the products. In a chemical equation, the reactants and products are written using chemical formulas.Scientists use a plus sign to separate the formulas of twoor more reactants or products. An arrow points from theformulas of the reactants to the formulas of the products.Carbon is the mainelement in charcoal.When charcoal burns,it reacts with oxygenin the air. The reactionproduces heat, light,and carbon dioxide.The formulas of thereactants are writtenbefore the arrow.The formulas of theproducts are writtenafter the arrow.C O 2CO 2A plus sign separatesthe formulas of twoor more reactants orthe formulas of twoor more products.The arrow, alsocalled the yields sign,separates the formulasof the reactants fromthe formulas of theproducts.READING CHECK5. Define What is a chemicalequation?TAKE A LOOK6. Identify List the reactantsand the products of the reaction in the figure. Use chemical symbols and chemicalformulas in your answer.reactants:products:Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook249Chemical Reactions
NameSECTION 2ClassDateChemical Formulas and Equations continuedCHECKING SYMBOLSREADING CHECK7. Explain Why is itimportant to check tomake sure that your chemicalformulas are correct?When you write a chemical formula, it is importantthat you check to make sure that it is correct. If you usethe wrong formula or symbol in an equation, the equationwill not describe the correct reaction. Even a small mistake can make a big difference.As an example, consider the three formulas Co, CO,and CO2. These formulas look very similar. However, thesubstances they represent are very different. Co is thesymbol for the element cobalt, a hard, bluish-grey metal.CO is the formula for carbon monoxide, a colorless, poisonous gas. CO2 is the formula for carbon dioxide, acolorless gas that living things give off when they breathe.Examples of Similar Symbols and FormulasSTANDARDS CHECKPS 1b Substances react chemically in characteristic ways withother substances to form newsubstances (compounds) withdifferent characteristic properties. In chemical reactions,the total mass is conserved.Substances often are placed incategories or groups if they reactin similar ways; metals is anexample of such a group.Word Help: chemicalof or having to do with theproperties or actions ofsubstances8. Explain How does abalanced chemicalequation show the law ofconservation of mass?CO2The chemicalformula for thecompound carbondioxide is CO2. Carbon dioxide is a colorless, odorless gasthat you exhale.COThe chemicalformula for thecompound carbonmonoxide is CO.Carbon monoxide isa colorless, odorless,and poisonous gas.CoThe chemical symbol for the elementcobalt is Co. Cobaltis a hard, bluishgray metal.CONSERVING MASSThe law of conservation of mass states that masscannot be lost or gained during a chemical reaction. Thetotal mass of the reactants in a chemical reaction is thesame as the total mass of the products. You can use this lawto help you figure out how to write a chemical equation.During a chemical reaction, atoms are not lost or gained.Every atom in the reactants becomes part of the products.Therefore, in a chemical equation, the numbers and kinds ofatoms in the reactants and products must be equal. In otherwords, the chemical equation must be balanced.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook250Chemical Reactions
NameSECTION 2ClassDateChemical Formulas and Equations continuedHOW TO BALANCE A CHEMICAL EQUATIONTo balance an equation, you must use coefficients. Acoefficient is a number that is placed in front of a chemical formula. For example, 2CO represents two carbonmonoxide molecules. The number 2 is the coefficient.For an equation to be balanced, all atoms must becounted. So you must multiply the subscript for each element in a formula by the formula’s coefficient. For example,2H2O contains a total of four hydrogen atoms and twooxygen atoms. Only coefficients, not subscripts, may bechanged when balancing equations. The figure below showsyou how to use coefficients to balance an equation.23Count the atoms ofeach element in thereactants and the products. Here, you can seethat there are moreoxygen atoms in thereactants than in theproducts. Therefore, thechemical equation isnot balanced.Add coefficients tobalance the atoms ofoxygen. There are twoatoms of oxygen in thereactants. Place thecoefficient 2 in front ofthe products to give twoatoms of oxygen in theproducts. Then, countthe atoms again. Now,the hydrogen atoms arenot balanced.Add coefficients tobalance the atomsof hydrogen. Add thecoefficient 2 to the H2reactant to give fouratoms of hydrogen in thereactants. Then, countthe atoms again todouble-check your work.ReactantsProductsH2 O2H 2OH 2O 2ProductsH2 O22H2OH 4 O 2O 2ReactantsProducts2H2 O22H2OH 410. Identify What can’t bechanged when balancing achemical equation?H 2 O 1ReactantsH 29. Describe What is acoefficient?READING CHECKFollow these steps to write a balanced equation forH2O.H2 O21READING CHECKH 4 O 2O 2Math Focus11. Applying ConceptsBalance the equation:Na Cl2NaClby putting coefficients whereneeded.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook251Chemical Reactions
NameClassDateSection 2 ReviewNSESPS 1bSECTION VOCABULARYchemical equation a representation of a chemical reaction that uses symbols to show therelationship between the reactants and theproductschemical formula a combination of chemicalsymbols and numbers to represent a substancelaw of conservation of mass the law that statesthe mass cannot be created or destroyed inordinary chemical and physical changesproduct a substance that forms in a chemicalreactionreactant a substance or molecule thatparticipates in a chemical reaction1. Compare How is a chemical equation different from a chemical formula?2. Identify Fill in the blank spaces in the table.Chemical equationNumber ofatoms in thereactantsNumber ofatoms in theproductsNa Cl2Na Na Cl Cl NaCl H2O H H Cl Cl Na Na O O Sb Sb I I NaClHCl NaOH2Sb 3I22SbI3Is the equationbalanced?3. Describe Give the names of the covalent compounds listed below.SiO2SbF34. Explain Why can’t you change the subscripts in a formula in order to balance achemical equation?5. Applying Concepts Balance the equation:Mg N2Mg3N2 by putting coefficients where needed.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook252Chemical Reactions
Physical Science Answer Key continued3. chemical bond4. When water boils, a new substance is not4. Changing the subscripts changes the sub-stance in the chemical reaction. Therefore,if you change subscripts, you change thechemical reaction that you are describing.5. 3Mg N2Mg3N2formed. The water vapor that forms duringboiling can condense into liquid water.5. The chemical properties of the material inthe beaker are different from those of theoriginal substances. This shows that a chemical reaction must have occurred.SECTION 3 TYPES OF CHEMICALREACTIONS1. a reaction in which two or more substancesSECTION 2 CHEMICAL FORMULAS ANDEQUATIONS2.3.4.5.1. the elements found in a substance and2.3.4.5.6.7.8.9.10.11.how many atoms of each element are in amoleculethreePCl33 a short way to show what happens ina chemical reaction using symbols andformulasReactants: C, O2Products: CO2If you use the wrong chemical formula, achemical equation will not describe thereaction you are trying to describe.A chemical equation shows that noatoms are lost or gained during a chemicalreaction.a number that is placed in front of achemical formulasubscripts2Na Cl22NaClReview1. synthesis and decomposition.2. Synthesis is the combination of two or moresubstances to make a new substance. The newsubstance cannot be an element, because it isa combination of at least two elements.3. double-displacement, decomposition,synthesis4. Aluminum must be less reactive thancalcium. In a single displacement reaction,a more reactive element replaces a lessreactive element.5. It appears to be a double-displacementreaction. A precipitate is often an indication that a new substance formed by theexchange of ions between two compoundsin the solutions.Review1. A chemical formula represents a substance.SECTION 4 ENERGY AND RATES OFCHEMICAL REACTIONSA chemical equation represents a chemicalreaction.2.ChemicalequationNumberof atomsin thereactantsNumberof atomsin theproductsIs theequationbalanced?Na Cl2NaClNa 1Cl 2Na 1Cl 1noHCl NaOHNaCl H2OH 2Cl 1Na 1O 1H 2Cl 1Na 1O 1yes2Sb 3I22SbI3Sb 2I 6Sb 2I 6yescombine to form a new compoundCA Ba new compound and the replaced elementmore reactivesynthesis, decomposition, single-displacement,and double-displacement reactions1.2.3.4.5.6.7.8.9.10.11.3. SiO2: silicon dioxideIt is released into the surroundings.It is absorbed from the surroundings.heat, light, and electricityEnergy cannot be created or destroyed.They must collide.the reactants to the highest point on the curveproductsReactions occur faster at higher temperatures.It increases the rate of reaction.The reaction rate is faster.Catalysts speed up reactions, and inhibitorsslow or stop them.SbF3: antimony trifluorideCopyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook Answer Key85Physical Science
Physical Science Answer Key continued3. chemical bond4. When water boils, a new substance is not4. Changing the subscripts changes the sub-stance in the chemical reaction. Therefore,if you change subscripts, you change thechemical reaction that you are describing.5. 3Mg N2Mg3N2formed. The water vapor that forms duringboiling can condense into liquid water.5. The chemical properties of the material inthe beaker are different from those of theoriginal substances. This shows that a chemical reaction must have occurred.SECTION 3 TYPES OF CHEMICALREACTIONS1. a reaction in which two or more substancesSECTION 2 CHEMICAL FORMULAS ANDEQUATIONS2.3.4.5.1. the elements found in a substance and2.3.4.5.6.7.8.9.10.11.how many atoms of each element are in amoleculethreePCl33 a short way to show what happens ina chemical reaction using symbols andformulasReactants: C, O2Products: CO2If you use the wrong chemical formula, achemical equation will not describe thereaction you are trying to describe.A chemical equation shows that noatoms are lost or gained during a chemicalreaction.a number that is placed in front of achemical formulasubscripts2Na Cl22NaClReview1. synthesis and decomposition.2. Synthesis is the combination of two or moresubstances to make a new substance. The newsubstance cannot be an element, because it isa combination of at least two elements.3. double-displacement, decomposition,synthesis4. Aluminum must be less reactive thancalcium. In a single displacement reaction,a more reactive element replaces a lessreactive element.5. It appears to be a double-displacementreaction. A precipitate is often an indication that a new substance formed by theexchange of ions between two compoundsin the solutions.Review1. A chemical formula represents a substance.SECTION 4 ENERGY AND RATES OFCHEMICAL REACTIONSA chemical equation represents a chemicalreaction.2.ChemicalequationNumberof atomsin thereactantsNumberof atomsin theproductsIs theequationbalanced?Na Cl2NaClNa 1Cl 2Na 1Cl 1noHCl NaOHNaCl H2OH 2Cl 1Na 1O 1H 2Cl 1Na 1O 1yes2Sb 3I22SbI3Sb 2I 6Sb 2I 6yescombine to form a new compoundCA Ba new compound and the replaced elementmore reactivesynthesis, decomposition, single-displacement,and double-displacement reactions1.2.3.4.5.6.7.8.9.10.11.3. SiO2: silicon dioxideIt is released into the surroundings.It is absorbed from the surroundings.heat, light, and electricityEnergy cannot be created or destroyed.They must collide.the reactants to the highest point on the curveproductsReactions occur faster at higher temperatures.It increases the rate of reaction.The reaction rate is faster.Catalysts speed up reactions, and inhibitorsslow or stop them.SbF3: antimony trifluorideCopyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook Answer Key85Physical Science
Chemical Formulas and Equations continued How Are Chemical Formulas Used to Write Chemical Equations? Scientists use chemical equations to describe reac-tions. A chemical equation uses chemical symbols and formulas as a short way to show what happens in a chemical reaction. A chemical equation shows that atoms are only rearranged in a chemical .
Writing Chemical Formulas and Chemical Reactions Chemical Formula Chemical formulas are a useful way to convey information about a compound such as: ¾ What elements make up the compound ¾ The ratio or number of atoms in the compound The chemical formula has different meanings depending on the type of intramolecular forces holding
Distinguish between chemical formulas, molecular formulas, and formula units. 4. Know the charges of the formulas for monatomic ions using the periodic table. Chapter 9 & 10 5. Be familiar with the charges and the formulas for polyatomic ions. 6. Apply the rules for naming and writing formulas for binary and ternary ionic compounds. 7.
SHOW FORMULAS If you ever want to see formulas in a spreadsheet’s cells, rather than the calculated answer to the formula, click the Show Formulas button in the Formula Auditing group of the Formulas tab. Formulas will appear in the spreadsheet
Calculate the percent composition by mass of each element in a compound or hydrate Name the four types of chemical reactions and give an example of each. Identify molecular formulas of substances Use molecular formulas to determine empirical formulas Use molecular formulas to represent structural formulas
Levenspiel (2004, p. iii) has given a concise and apt description of chemical reaction engineering (CRE): Chemical reaction engineering is that engineering activity concerned with the ex-ploitation of chemical reactions on a commercial scale. Its goal is the successful design and operation of chemical reactors, and probably more than any other ac-File Size: 344KBPage Count: 56Explore further(PDF) Chemical Reaction Engineering, 3rd Edition by Octave .www.academia.edu(PDF) Elements of Chemical Reaction Engineering Fifth .www.academia.eduIntroduction to Chemical Engineering: Chemical Reaction .ethz.chFundamentals of Chemical Reactor Theory1www.seas.ucla.eduRecommended to you b
SECTION 2 Name Class Date Chemical Formulas and Equations continued FORMULAS FOR COVALENT COMPOUNDS In many cases, the name of a covalent compound tells you how to write its chemical formula. This is because the names of many covalent compounds use prefixes. Prefixes re
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