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Chapter 16
Chemical Reactions That Involve Heat
The study of the changes in heat in chemical reactions.
Thermochemistry
Chemical Reactions Involve ENERGY
Changes in ENERGY result from bonds being broken and new bonds being formed.
Requires ENERGY
Breaking Bonds
Releases ENERGY
Bond Formation
Both absorption and release of energy occurs.
In a chemical reaction
We detect the net result.
Measure the temperature of the surroundings.
System: Reactants and Products
System & Surroundings
Surroundings: Solvent, container, atmosphere above the reaction, etc.
Types of Reactions
RELEASE HEAT!
Exothermic Reactions
CC33HH88(g)(g) + 5O+ 5O22(g)(g)
3CO3CO22(g)(g) + 4H+ 4H22OO(g)(g) + 2043 kJ+ 2043 kJ
Combustion reactions are exothermic!
HEAT is listed as a product in the reaction! HEAT ENERGY
Exothermic Reactions Energy
needed to break bonds must be LESS THAN the energy released when new bonds are formed.
Surroundings will have a higher
temperature after the reaction!
NaOH(s) Na+(aq) + OH-
(aq)
Beginning Temp of Surroundings: 25.4°C
Ending Temp of Surroundings: 29.5°C
Change in Temp of Surroundings: +4.1°C
+4.1°C
Means heat was GIVEN OFF
EXOTHERMIC
NaOH(s) Na+(aq) + OH-
(aq)
+4.1°CCalculate HEAT per MOLE if you have 5.0 grams of NaOH to start.
5.0 g NaOH
40 g NaOH
1 mol NaOH 0.125 mol NaOH=
+4.1°C
0.125 mol NaOH= + 33°C per mole NaOH
Means HEAT is given off.
ABSORB HEAT!
Endothermic Reactions
CC (s)(s) + H+ H22O O (g)(g) + 113 kJ+ 113 kJ
COCO (g)(g) + H+ H22 (g)(g)
HEAT is listed as a reactant in the reaction!
HEAT ENERGY
Endothermic Reactions The energy
needed to break bonds is GREATER THAN the energy released when new bonds are formed.
Surroundings will have a lower
temperature after the reaction!
Exo & Endo Demos
Fireworks
More about fireworks