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Grade 9 ChemistryChemical Equations - Students’ notesName:……………………Date:Evidence of a chemical reaction:A reaction has occurred if the chemical and physical properties of the reactants and products differ.For a reaction to occur, particles of reactants must collide, and with sufficient energy .Name 5 evidences for a chemical reaction.Chemical reactions result in chemical changes.Chemical changes occur whennew substances are created.The original substance(s), calledreactants, change into new substance(s) calledproducts.Chemical reactions can be written in different ways: word equations or symbolic equations1
Reaction Conditions and TerminologyCertain symbols give more info about a reaction.(s)= solid(l)= liquid(g)= gas(aq)= aqueous (dissolved in H2O) (solution)*Note:*More on aqueous-- “soluble” or “in solution” also indicate that a substance is dissolved in water (usually)-- acids are aqueous solutions.Continue Other symbols…means “yields” or “produces”means heat is added to the reactionMgCO3(s)MgO(s)+CO2(g)Temp. at which we perform rxn. might be given:C6H5Cl+NaOHC6H5OH+NaClThe catalyst used might be given.C2H4(g)+H2(g)C2H6(g)Precipitate:a solid product that forms in an aqueous solution reaction.2NaCl(s)NaCl(aq)400oCPt
Balancing Chemical EquationsLaw of Conservation of MassWhen a chemical reaction occurs, new compounds are created, BUT…No new matter is created or destroyed; atoms are justrearrangedas the atomschange partnersto form new compounds.If there are 3 atoms of oxygen in the reactants, there MUST be3atoms of oxygen inthe products.Number of each atom in reactants = number of each atom in products.The law of conservation of mass:Mass of reactants = mass of productsThe simplest form of chemical equation is aword equation.Potassium metal + oxygen gaspotassium oxide-Asymbolic equationshows the formulas of the elements/compounds.-A symbolic equation shows which atoms are involved, but not how many molecules areinvolved.K + O2K2O-Abalanced symbolic chemical equationshows all atoms and thecoefficientstells us howmany molecules (and atoms) there are.-Balancingensuresthat thenumber of each atomis thesame on both sidesof the reactionarrow.4K+ O22K2O3
Using the law of conservation of mass, we cancount atoms to balancethe number of atomsin chemical equations.Word equation:methane + oxygenwater + carbon dioxideChemical equation (unbalanced):CH4+ O2H2O + CO2To balance the compounds, take note of how manyatoms of each element occur on each side of the reaction arrow.EX.Solid iron reacts with oxygen gas to yield solid iron (III) oxide__ Fe(s)+__ O2(g)__ Fe2O3(s)If all coefficients are 1… this will violate------------------------------ Law.

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Term
Spring
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Tags
Chemistry, Chemical reaction, Ion, Sodium chloride

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