Double Replacement Reaction:

• Parts of two compounds switch places to form two new compounds

• Two reactants yield two products.

Al2(SO4)3 (s) + 3NH4OH (aq)

2Al(OH)3 (s) + 3NH4SO4 (aq)

MgSO4 (s) + 2NH4OH (aq)

Mg(OH)2 (s) + (NH4)2SO4 (aq)

Double Replacement(Swap ‘hats’)

Single Replacement(new couple)

Synthesis( 2 becomes 1)

+Decomposition(1 becomes 2)

Which type of reaction is shown?

2 Ca (s) + O2 (g) 2 CaO (s)

MgCO3 (s) MgO (s) + CO2 (g)

Cu (s) + 2 AgNO3 (aq) Cu(NO3)2 (aq) + 2 Ag (s)

3AgNO3 (aq) + Na3PO4 (aq) Ag3PO4 (s) + 3NaNO3 (aq)

Synthesis

Single Replacement

Decomposition

Double Replacement

2 HgO (s) 2Hg (l) + O2 (g)

Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)

BaCl2 (aq) + Na2SO4 (aq) BaSO4 (s) + 2 NaCl (aq)

H2 (g) + Cl2 (g) 2 HCl (g)

Double Replacement

Single Replacement

Decomposition

Synthesis

Heat and Chemical Change

Active IngredientsKClNaClNH2CONH2 (urea)C7O6H14 (methyl-D-glucopyranoside; a surfactant)

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What have we learned?

Sometimes heat is given off during a chemical reaction.This makes it feel hotter.

Sometimes heat is absorbed during a chemical reaction.This makes it feel colder.

What causes it to be different?

• Chemical bonds contain energy.

• Add the energy of all of the bonds in the reactants together to find their total energy.

• Add the energy of all of the bonds in the products together to find their total energy.

• If the two numbers aren’t the same (and they almost never are), then there will be heat energy given off or taken in.

2 H2 + O2 2 H2O

Energy

2 H2 + O2

2 H2O

•If the products contain less energy, energy must have been given off during the reaction.

Energy barrier

2 H2 + O22 H2O

Energy

2 H2 + O2

2 H2O

•If the products contain more energy, energy must have been absorbed during the reaction.

Energy barrier

If heat energy is given off during a reaction, it is called an EXERGONIC or an EXOTHERMIC REACTION.

Heat exits = exergonic = exothermic

Exergonic reactions can be recognized by a temperature INCREASE.

If heat energy is absorbed during a reaction, it is called an ENDERGONIC or an ENDOTHERMIC REACTION.

Heat enters = endergonic = endothermic

Endergonic reactions can be recognized by a temperature DECREASE.

Rates of Reactions

Vs.

December 1977 in Westwood, LAGrain elevator explosion

August 10, 2003 in Columbus, OHFlour mill explosion

January 29, 2003 in Kinston, NC West Pharmaceutical Services

chemed.chem.purdue.edu/demos/main_pages/5.14.html

QuickTime Movie

OHCOO)OHC( 222n6126 xsflour

Air-borne dust ???

Flour

Pile Slow

Rate of Reaction

[dust] > 50 g/m3

NC Competency Goal 4.03

Assess reaction rates and factors that affect reaction rates.

And by the letter

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