Thermodynamics

Unit 10

Endothermic vs. Exothermic

• Endo – chemical absorbs or takes in energy or heat

• Exo – chemical produces or gives off energy or heat

• Remember BARF!

• Chemical Energy Change:

• Endo – increases, chemical gains PE

• Exo – decreases, chemical loses PE

Endothermic vs. Exothermic

• Thermal Energy Change of Surroundings:

• Endo – decreases, surroundings (often H2O) lose KE

• Exo – increases, surroundings (often H2O) gain KE

Endothermic vs. Exothermic

Endothermic vs. Exothermic

• Temperature of Surroundings (often H2O or solution):

• Endo – decreases

• Exo - increases

• Energy Transformation

• Endo – thermal chemical

KE PE

• Exo – chemical thermal

PE KE

Endothermic vs. Exothermic

• Examples:

• Endo – melting, boiling, evaporation, cold pack

• Exo – burning, explosions, freezing, condensation, hot pack

Endothermic vs. Exothermic

• Model

• Chemical could be ice or other substance

• H2O represents surroundings

Endothermic vs. Exothermic

• Endothermic

Endothermic vs. Exothermic

chemical

H2O H2OT decreases

heat heat

heat

• Exothermic

chemical

H2O H2OT increases

heat heat

heat

Endothermic vs. Exothermic

• Graphs of Potential Energy– Endothermic

Endothermic vs. Exothermic

PE

Reaction Coordinate

Reactants

Products

E in

Note: Chemical

E increasing

• Graphs of Potential Energy– Exothermic

Endothermic vs. Exothermic

PE

Reaction Coordinate

Reactants

Products

E out

Note: Chemical

E decreasing

H = Molar Heat

1. H represents:

PE (heat content) of products or reactants

a.k.a. “enthalpy”

Endothermic vs. Exothermic

2. H is the change in heat content

H = Hproducts – Hreactants

(Find H by reading the PE graph.)

Endothermic vs. Exothermic

3. Endothermic products have more H, that means the molar heat is positive.

4. Exothermic products have less H, that means the molar heat is negative.

Endothermic vs. Exothermic