A chemical change must occur as it is the result of a chemical reaction. A reaction could include...
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Transcript of A chemical change must occur as it is the result of a chemical reaction. A reaction could include...
Chemical Reactions
In chemistry, a reaction occurs when two or more substances interact and
something happens.
KEY POINTS
A chemical change must occur as it is the result of a chemical reaction.
A reaction could include ions, molecules, or pure atoms (elements).
Energy of Chemical Reactions
Endothermic Exothermic
Endothermic
Energy – absorbed Required for reaction Absorbed energy - often
heat or electrical energy.
Exothermic
Energy - released Released energy - originally stored
in bonds of reactants Often heat given off causes
product(s) to feel hot. Reactions involving combustion or
burning are exothermic chemical reaction.
REACTION TYPES
SYNTHESIS (Combination) DECOMPOSITION SINGLE REPLACEMENT
(Displacement) DOUBLE REPLACEMENT
(Double Displacement) COMBUSTION
Synthesis
Two or more reactants yielding one product is a way to identify a synthesis reaction.
Generic Example:
A + B ABH2 + O H2O
Synthesis Example
Simple hydrogen gas combined with simple oxygen gas can produce a more complex substance --- water!
S + O2 SO2reactant + reactant -------> product
Decomposition
A more complex substance (reactant) breaks down into its more simple parts (products).
AB A + B Synthesis and decomposition
reactions are opposites. catalyst – a substance that causes or
accelerates a chemical reaction without itself being affected.
Decomposition Example
Water can be broken down into hydrogen gas and oxygen gas.
2H2O 2H2
+ O2reactant -------> product + product
Single Replacement
In a single replacement reaction a single uncombined element replaces another in a compound. Two reactants yield two products.
A + BC AC + B Mg + 2AgNO3 Mg(NO3)2
+ 2Ag
Single Replacement Example
When zinc combines with hydrochloric acid, the zinc replaces hydrogen.
Zn + 2HCl ZnCl2 + H2
reactant + reactant ------> product + product
Demonstration Time!
Double Replacement
In a double replacement reaction parts of two compounds switch places to form two new compounds. Two reactants yield two products.
AB + CD AD + CBprecipitate - to separate (a substance)
in solid form from a solution, as by means of a chemical reaction.
Double Replacement Example
When silver nitrate combines with sodium chloride, two new compounds are formed --silver chloride and sodium nitrate -- because the sodium and silver switched places.
AgNO3 + NaCl AgCl + NaNO3
Combustion
Combustion reactions always involve molecular oxygen O2.
Anytime anything burns (in the usual sense), it is a combustion reaction.
Combustion reactions are almost always exothermic (i.e., they give off heat).
Works Cited
Howcast. " YouTube - Balancing Chemical Equations - H2O ." YouTube - Broadcast Yourself. . N.p., n.d. Web. 5 Mar. 2011. <http://www.youtube.com/watch?v=jdUQzVMB4Hw&feature=player_embedded>.
"Types of Chemical Reactions." Utah State Office of Education - USOE - Welcome. N.p., n.d. Web. 5 Mar. 2011. <http://schools.utah.gov/curr/science/sciber00/8th/matter/sciber/chemtype.htm>.
brightstorm2. " YouTube - Decomposition Reaction ." YouTube - Broadcast Yourself. . N.p., n.d. Web. 5 Mar. 2011. <http://www.youtube.com/watch?v=yuStJotow2I>.
"chemical reactions:combustion." Indiana University Northwest. N.p., n.d. Web. 5 Mar. 2011. <http://www.iun.edu/~cpanhd/C101webnotes/chemical%20reactions/combustion.html>.
ochem9. " YouTube - Five Major Chemical Reactions ." YouTube - Broadcast Yourself. . N.p., n.d. Web. 5 Mar. 2011. <http://www.youtube.com/watch?v=tE4668aarck>.
tszheichoi. " YouTube - Hygrogen and oxygen from water ." YouTube - Broadcast Yourself. . N.p., n.d. Web. 5 Mar. 2011. <http://www.youtube.com/watch?v=OTEX38bQ-2w&feature=related>.
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