Characteristics & Types of Chemical Reactions

Transcription

1 Characteristics & Types of Chemical Reactions

2 What is a chemical reaction? Another name for a chemical change Bonds break and atoms of one or more substances are rearranged and new bonds form New substance(s) formed with different properties

3 Indicators of a Chemical Reaction Color change Light formation Gas bubbles Precipitate formation Temperature change

4 Color Change The color of a substance may change when its chemical composition changes. An example of a color change as evidence of a chemical reaction is seen when crystal violet dye is added to a solution containing hydroxide ions. The intensity of the color decreases over time until it disappears. The product of the reaction is colorless in water solution. A color change represents more than just a physical change such as diluting a substance or adding food color to a substance. These physical changes are not evidence of chemical reactions.

5 Light Formation The burning of logs in a fireplace is the reaction of the wood and oxygen along with a heat initiation source. Wood is made of cellulose, a combination of different substances that contain carbon, hydrogen, and oxygen. When this combustion reaction occurs, a large amount of energy is produced in the form of both heat and light. Chemical reactions can also be seen in the bright light and heat in fireworks displays. Glowing sticks also produce light when chemicals in the tube react and emit not heat, but a fluorescent glow.

6 Gas Formation When gas is produced during a reaction, it is also evidence of a new substance formed. For example, when baking soda (solid) is mixed with vinegar (liquid), carbon dioxide (gas) is one of the products formed. The new products formed from this reaction, including CO2 gas, have properties different from the original reactants.

7 Precipitate Formation In precipitation reactions, a precipitate is a solid substance that forms and separates from a solution. A precipitate often settles to the bottom of a liquid reaction. A precipitate forms because the solid produced is insoluble in aqueous solutions. This is a new substance formed with new properties and is evidence of a chemical change. An example in nature of this type of precipitation is the formation of minerals as water-insoluble compounds. Pipes in our homes get clogged because precipitates of magnesium and calcium oxides have deposited themselves within the pipes. This can happen with hard water. A classic example of precipitate formation is the combination of calcium chloride (road deicing salt) with sodium carbonate (caustic cleaning agent) which produces sodium chloride (table salt) and calcium carbonate (chalk).

8 Temperature Change Temperature changes indicate the formation of new substances. Chemical reactions can either give off heat or use heat: Endothermic Reactions: energy is absorbed (temperature decrease should be observed, but may be negligible) Exothermic Reactions: energy is released in the form of heat (temperature increase should be observed)

9 Indicators of a Chemical Reaction Video

10 Law of Conservation of Mass During a chemical reaction, matter is neither created not destroyed. This means all atoms present at the start of the reaction are present at the end.

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12 A STORY OF SYNTHESIS

13 Napoleon had been crushing on Deb for a while and then Synthesis happened!! Napoleon Deb Pure chemistry!! + (Reactants) (Product)

14 /Synthesis/ The get-together Two or more chemicals bond together forming one new substance.

15 /Synthesis/ The get-together A + B AB

16 /Synthesis/ The get-together

17 The BREAK-UP!!

18 Say it isn t so!!! Jelena Justin Selena + (Reactant) (Products) DECOMPOSITION!!!!!!

19 /Decomposition/ The break-up

20 /Decomposition/ The break-up One substance breaks down into two or more separate substances.

21 /Decomposition/ The break-up AB A + B

22 /Decomposition/ The break-up 2H 2 O 2 2H 2 O + O 2

23 The CHEATER!!

24 Kermit & Miss Piggy Denise Kermit & Denise + + Miss Piggy (Reactants) I heard it through the grapevine!! (Products)

25 /Single Replacement/ The cheater

26 /Single Replacement/ The cheater One element knocks another element out of a compound.

27 /Single Replacement/ The cheater AB + X AX + B

28 /Single Replacement/ The cheater 2HCl + Zn ZnCl 2 + H 2

29 The SWAP!

30 At the start of the dance... David Tiffany Brandon Brittany + But once the music and dancing started... David Brittany Brandon Tiffany +

31 /Double Replacement/ The swap

32 /Double Replacement/ The swap Two compounds switch ions with each other.

33 /Double Replacement/ The swap AB + XY AX + BY

34 /Double Replacement/ The swap BaCl 2 + Na 2 SO 4 BaSO 4 + 2NaCl

35 What a dance!!