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Chemical. Reactions. Did a Chemical Reaction Take Place?. There are several ways to tell if a chemical reaction has occurred… Temperature change Color change Odor Precipitate is formed (solid) Gas is formed. Writing Chemical Equations. - PowerPoint PPT Presentation

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  • ChemicalReactions

  • Did a Chemical Reaction Take Place?There are several ways to tell if a chemical reaction has occurredTemperature changeColor changeOdorPrecipitate is formed (solid)Gas is formed

  • Writing Chemical EquationsA substance that undergoes a reaction is called a reactant.Reactants are written on the left of the arrowWhen reactants undergo a chemical change, each new substance formed is called a product.Products are written on the right of the arrowReactants Products

  • Writing Chemical EquationsReactants starting chemicalProducts substances that are formed+ separates substances (usually read as and) separates reactants from products (usually read as gives, produces, or yields)

  • Word EquationsThe simplest way to represent a reaction is by using words to describe all the reactants and products, with an arrow placed between them to represent change.Reactants are placed to the left of the arrow, and products are placed to the right.Plus signs are used to separate reactants and also to separate products.VinegarBaking Soda

  • Chemical EquationsWord equations describe reactants and products, but they are long and awkward and do not adequately identify the substances involved.Word equations can be converted into chemical equations by substituting chemical formulas for the names of compounds and elements.

  • Chemical EquationsThe equation for the reaction of vinegar and baking soda can be written using the chemical formulas of the reactants and products.

    By examining a chemical equation, you can determine exactly what elements make up the substances that react and form.

  • Chemical ReactionsIt may also be important to know the physical state of each reactant and product.Symbols in the parentheses are put after formulas to indicate the state of the substance.Solids, liquids, gases, and in water (aqueous) solutions are indicated by the symbols (s), (l), (g), and (aq).

  • Try this exampleWrite the skeleton equation for solid magnesium reacting with oxygen gas to give solid magnesiumMg (s) + O2 (g) MgOYou can see that you have to remember how to write formulas and what elements are diatomic in order to write equations!

  • Balancing Chemical EquationsThe mass of the products is always the same as the mass of the reactants that react to form them.The law of conservation of mass summarizes these findings. Matter is neither created nor destroyed during a chemical reaction.What you start with has to equal what you end with

  • Balancing Chemical EquationsFor a chemical equation to accurately represent a reaction, the same number of each kind of atom must be on the left side of the arrow as are on the right side.

  • Steps for Balancing Chemical EquationsWrite the skeleton equation for the reactionCount the number of atoms of each element of the reactantsCount the number of atoms of each element of the reactantsAdd / Change the coefficients to make the numbers of each element equalYOU CAN NEVER CHANGE A SUBSCRIPT!Write the coefficients in the lowest possible ratioCheck your work

  • ExamplesWrite the balanced chemical equation for the reaction between hydrogen and chlorine to give hydrochloric acidH2 + Cl2 HCl H 2 H - 1Cl 2 Cl 1 H2 + Cl2 2HCl H 2 H - 2Cl 2 Cl 2

  • More examplesWrite and balance the reaction between sodium hydroxide and calcium bromide to give calcium hydroxide and sodium bromide 2 NaOH + CaBr2 Ca(OH)2 + 2NaBr

  • More examplesWrite and balance the reaction for potassium iodide reacting with lead (II) nitrate to form potassium nitrate and lead (II) iodide 2 KI + Pb(NO3)2 2 KNO3 + PbI2

  • Classification of ReactionsThere are 5 major classifications of reactions:Synthesis (Combination)DecompositionCombustionSingle Replacement Double Replacement (Metathesis)

  • Synthesis (Combination)Synthesis when 2 or more substances react to produce 1 productOf the form: A + B ABExamples:2 Fe + 3 Cl2 2 FeCl32 Na + Cl2 2NaClCaO + H2O Ca(OH)2Mg + O2 MgO

  • DecompositionDecomposition when a single compound breaks down into 2 or more compoundsOf the form: AB A + B Note that this is the exact opposite of synthesisExamples:2 Na3N 2 Na + 3 N2NH4NO3 N2O + 2H2O2H2O H2 + O2

  • CombustionCombustion when O2 combines with a hydrocarbon to form CO2 and H2OOf the form: hydrocarbon + O2 CO2 + H2OFor example:2CH4 + O2 CO2 + 2H2O2CH3OH + 3O2 2CO2 + 4H2O

  • When Balancing Combustion ReactionsPut a two in front of the hydrocarbon to start. Balance them in the order C, H, OMake sure your answer is in the lowest whole number ratio

  • Single ReplacementSingle Replacement when the atoms of one element replace the atoms of another element in a compoundOf the form : A + BX B + AXFor example:2 Li + 2HOH 2 LiOH + H2Cu + 2AgNO3 2 Ag + Cu(NO3)2

  • Activity Series

  • Single Replacement ReactionsIn order for a single replacement reaction to occur, the element that is by itself must be strong enough to push the other element out of the way.The activity series show you the relative pushing power of the elements.In order for the reaction to occur, the lone element must be above the element in the compoundOtherwiseNO REACTION NR

  • Single Replacement ReactionsYou need to know which chart you are to look atmetals or halogens.A metal can replace another metalA halogen can replace another halogen

  • Will these reactions occur?Will the following reaction occur? If so, complete and balance the reaction.Ag + Cu(NO3)2 Ag + Cu(NO3)2 NRNo reaction because Ag is below Cu in the Activity series of metals

  • Will these reactions occur?Will the following reaction occur? If so, complete and balance the reaction.Mg + AlCl3 3Mg + 2AlCl3 3MgCl2 + 2 AlThe reaction WILL occur because Mg is above Al in the activity series

  • Will these reactions occur?Will the following reaction occur? If so, complete and balance the reaction.Br2 + MgCl2 Br2 + MgCl2 NRThis reaction will NOT occur because Br is not above Cl in the activity series of halogens

  • Double Replacement (Metathesis)Double Replacement a reaction involving the exchange of ions between 2 compoundsOf the form: AX + BY BX + AYExamples:Pb(NO3)2 + 2KI PbI2 + 2KNO3Na2CO3 + 2AgNO3 2NaNO3 + Ag2CO3

  • Double Replacement (Metathesis)In order for a double replacement reaction to take place, one of 3 things must be formed:Precipitate (solid)GasWeak electrolyte usually water

  • Solubility Rules

  • Soluble or Insoluble?Classify the following as soluble or insoluble? (Hint: insoluble means precipitate)NaCO3SolublePbSO4Insoluble (precipitate)Co(OH)2Insoluble (precipitate)Ba(NO3)2Soluble(NH4)3PO4soluble

  • Reactions with a gasCarbonates, bicarbonates, and sulfides react with acids to form a gasFor example:HCl + Na2S 2HCl + Na2S H2S (g) + 2NaClThe sulfide or carbonate formed will result in the gas

  • Reactions with a gasHCl + NaHCO3 HCl + NaHCO3 H2CO3 (g) + NaClHCl + NaHCO3 H2O + CO2 (g) + NaCl

  • Will these reactions occur?Will the following reaction occur? If so, complete and balance the reaction.Na2CO3 + AgNO3 Na2CO3 + AgNO3 Ag2CO3 + NaNO3Na2CO3 + AgNO3 Ag2CO3 (s) + NaNO3Na2CO3 + 2AgNO3 Ag2CO3 (s) + 2NaNO3

  • Will these reactions occur?Will the following reaction occur? If so, complete and balance the reaction.HCl + NaOH HCl + NaOH NaCl + HOHHCl + NaOH NaCl + H2O

  • Will these reactions occur?Will the following reaction occur? If so, complete and balance the reaction.NaOH + K2SO4 NaOH + K2SO4 Na2SO4 + KOHNaOH + K2SO4 Na2SO4 (aq) + KOH (aq)NaOH + K2SO4 NR