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

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