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Chemical Reactions Chemical Reactions: takes place when one or more substances change into new substances. Starting substances: Reactants Formed substances:Products.

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Presentation on theme: "Chemical Reactions Chemical Reactions: takes place when one or more substances change into new substances. Starting substances: Reactants Formed substances:Products."— Presentation transcript:

1 Chemical Reactions Chemical Reactions: takes place when one or more substances change into new substances. Starting substances: Reactants Formed substances:Products

2 Chemical Reactions Chemical Property: the ability of a substance to undergo a chemical reaction and form new substances. A chemical change always results in a change in chemical compositionChemical Property: the ability of a substance to undergo a chemical reaction and form new substances. A chemical change always results in a change in chemical composition Examples: burn, rust, decompose, ferment, explode, corrodeExamples: burn, rust, decompose, ferment, explode, corrode Reactants change into, produce Products Iron and Sulfur Iron sulfide

3 Reactants change into, produce Products Iron and Sulfur Iron sulfide Chemical Reaction

4 Chemical Reactions Energy is always absorbed or given off in a chemical reactionEnergy is always absorbed or given off in a chemical reaction Evidence of a chemical reaction: change in color or odor, gas or solid formed from a liquid, irreversibility of a reactionEvidence of a chemical reaction: change in color or odor, gas or solid formed from a liquid, irreversibility of a reaction Conservation of Mass: in any physical or chemical reaction, mass is neither created nor destroyed; it is conserved.Conservation of Mass: in any physical or chemical reaction, mass is neither created nor destroyed; it is conserved. Mass of Product = Mass of ReactantMass of Product = Mass of Reactant

5 Examples of Chemical Reactions A silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, the black material we call tarnish. 2 Ag + S Ag 2 SA silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, the black material we call tarnish. 2 Ag + S Ag 2 S An iron bar rusts. The iron reacts with oxygen in the air to make rust. 4 Fe + 3 O 2 2 Fe 2 O 3An iron bar rusts. The iron reacts with oxygen in the air to make rust. 4 Fe + 3 O 2 2 Fe 2 O 3 Methane burns. Methane combines with oxygen in the air to make carbon dioxide and water vapor. CH O 2 CO H 2 OMethane burns. Methane combines with oxygen in the air to make carbon dioxide and water vapor. CH O 2 CO H 2 OMethane An antacid (calcium hydroxide) neutralizes stomach acid (hydrochloric acid). Ca(OH) HCl CaCl H 2 OAn antacid (calcium hydroxide) neutralizes stomach acid (hydrochloric acid). Ca(OH) HCl CaCl H 2 O Glucose (simple sugar) ferments to ethyl alcohol and carbon dioxide. The sugar in grapes or from grain ferments with yeast to make the alcohol and carbon dioxide. The carbon dioxide is the gas that bubbles out of beer or champaign. C 6 H 12 O 6 (glucose) 2 C 2 H 5 OH (ethyl alcohol) + 2 CO 2Glucose (simple sugar) ferments to ethyl alcohol and carbon dioxide. The sugar in grapes or from grain ferments with yeast to make the alcohol and carbon dioxide. The carbon dioxide is the gas that bubbles out of beer or champaign. C 6 H 12 O 6 (glucose) 2 C 2 H 5 OH (ethyl alcohol) + 2 CO 2

6 Review Physical or Chemical Change Cookies are bakedCookies are baked Water boilsWater boils Salt dissolves in waterSalt dissolves in water A firefly emits lightA firefly emits light Milk spoilsMilk spoils A metal chair rustsA metal chair rusts ChemicalChemical PhysicalPhysical ChemicalChemical

7 Review State the difference between a physical and chemical change In a chemical change, the chemical composition of the reactants changes as product(s) are formed. In a physical change, the chemical composition of the substance remains the same even if its physical appearance changesIn a chemical change, the chemical composition of the reactants changes as product(s) are formed. In a physical change, the chemical composition of the substance remains the same even if its physical appearance changes In a physical change, the chemical composition of the reactants changes as product(s) are formed. In a chemical change, the chemical composition of the substance remains the same even if its physical appearance changes In a physical change, the chemical composition of the reactants changes as product(s) are formed. In a chemical change, the chemical composition of the substance remains the same even if its physical appearance changes

8 Review State several physical or chemical properties that could be used to distinguish between each of the following pairs of substances and mixturesState several physical or chemical properties that could be used to distinguish between each of the following pairs of substances and mixtures Gasoline and WaterGasoline and Water color, odor, reaction upon heating, boiling pointcolor, odor, reaction upon heating, boiling point Copper and SilverCopper and Silver color, melting point, reactions with other substances, hardness, brittleness, strengthcolor, melting point, reactions with other substances, hardness, brittleness, strength Water and Salt Water SolutionWater and Salt Water Solution boiling point, freezing point, densityboiling point, freezing point, density

9 Review Which properties are physical and which are chemical? Reaction upon heatingReaction upon heating ColorColor OdorOdor Boiling pointBoiling point Melting pointMelting point HardnessHardness Reaction with other substancesReaction with other substances BrittlenessBrittleness StrengthStrength Freezing pointFreezing point DensityDensityPhysical ColorColor OdorOdor Boiling pointBoiling point Melting pointMelting point HardnessHardness BrittlenessBrittleness StrengthStrength Freezing pointFreezing point DensityDensityChemical Reaction upon heatingReaction upon heating Reaction with other substancesReaction with other substances


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