Investigating Chemical ReactionsInvestigating Chemical Reactions

All chemical reactions involve theAll chemical reactions involve thereleaserelease

ororAbsorption Absorption of energy. of energy.

Energy can be in the formEnergy can be in the form ofof

heatheat,, lightlight,, electricityelectricity andand soundsound..

Energy-releasing reactions are calledEnergy-releasing reactions are called

exothermicexothermic..An example would be an explosion.An example would be an explosion.

In an exothermic equation

the energy

Is written on the

Product side

Ex:C6H12O6 + O2 CO2 + H2O + Thermal

energy

Energy-absorbing reactions areEnergy-absorbing reactions are

endothermicendothermic..

An example would be cooking, or An example would be cooking, or cold packs.cold packs.

Chemists classify reactions to make Chemists classify reactions to make it easier to predict the products of it easier to predict the products of

reactions.reactions.

Synthesis Reactions(also called Combination or

Composition Reactions)

General Equation:General Equation:

X + Y X + Y XY XY

Example:Example: 2H2H2 (g) 2 (g) + O+ O2 (g) 2 (g) 2H 2H22O O ((ll) ) + thermal + thermal

energy energy

Decomposition ReactionsDecomposition Reactions

General Equation:General Equation:

XY XY X + Y X + Y

Example:Example:2H2H22O O ((ll) ) + thermal + thermal 2H2H2 (g) 2 (g) + O+ O2 (g)2 (g)

energyenergy

Practice Questions:Practice Questions:

Identify each of the following Identify each of the following reactions as exothermic or reactions as exothermic or

endothermic, and indicate the type endothermic, and indicate the type and balance the equation.and balance the equation.

thermal energy + Nthermal energy + N2(g) 2(g) + O+ O2(g) 2(g) NO NO2(g)2(g)

endothermic or exothermic?endothermic or exothermic?endothermicendothermic

Type and balanced equation:Type and balanced equation:

thermal energy + Nthermal energy + N2(g) 2(g) + 2O+ 2O2(g) 2(g) 2NO 2NO2(g)2(g)

Synthesis Chemical ReactionSynthesis Chemical Reaction

NaNa(s)(s) + Cl + Cl2(g) 2(g) NaCl NaCl(s) (s) + thermal energy+ thermal energy

endothermic or exothermic?endothermic or exothermic?

exothermicexothermic

Type and balanced equation:Type and balanced equation:

2Na2Na(s)(s) + Cl + Cl2(g) 2(g) 2NaCl 2NaCl(s) (s) + thermal energy+ thermal energy

Synthesis Chemical ReactionSynthesis Chemical Reaction

thermal energy + CHthermal energy + CH33CHCH22OHOH((ll)) C C(s)(s) + H + H2(g) 2(g) + O+ O2(g)2(g)

exothermic or endothermic?exothermic or endothermic?

endothermicendothermic

balanced equation:balanced equation:thermal energy +thermal energy + 2CH2CH33CHCH22OHOH((ll) ) 4C 4C(s)(s) + 6H + 6H2(g) 2(g) + O+ O2(g)2(g)

Decomposition Chemical ReactionDecomposition Chemical Reaction

Write skeleton equations for the Write skeleton equations for the following. Then tell if the following. Then tell if the

reaction is synthesis or reaction is synthesis or decomposition. Finally, decomposition. Finally,

balance the equation.balance the equation.

calcium + oxygen gas calcium + oxygen gas calcium oxide calcium oxideskeleton equation:skeleton equation:

Ca + OCa + O2 2 CaO CaO

synthesis or decomposition?synthesis or decomposition?Synthesis Chemical ReactionSynthesis Chemical Reaction

Balanced equationBalanced equation

2Ca + O2Ca + O2 2 2CaO 2CaO

Balanced chemical equationBalanced chemical equation

2Ca2Ca(s)(s) + O + O2(g) 2(g) 2CaO 2CaO(s)(s)

copper(II) oxide copper(II) oxide copper + oxygen gas copper + oxygen gasskeleton equation:skeleton equation:

CuO CuO Cu + O Cu + O22

synthesis or decomposition?synthesis or decomposition?Decomposition Chemical ReactionDecomposition Chemical Reaction

Balanced equationBalanced equation

2CuO 2CuO 2Cu + O 2Cu + O22

Balanced chemical equationBalanced chemical equation

2CuO2CuO(s)(s) 2Cu 2Cu(s)(s) + O + O2(g)2(g)

More work/More work/

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