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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