Thermodynamics Unit 10 Endothermic vs Exothermic Endo chemical

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!

Endothermic vs. Exothermic • 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 H 2 O) lose KE • Exo – increases, surroundings (often H 2 O) gain KE

Endothermic vs. Exothermic • Temperature of Surroundings (often H 2 O or solution): • Endo – decreases • Exo - increases

Endothermic vs. Exothermic • 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 • H 2 O represents surroundings

Endothermic vs. Exothermic • Endothermic H 2 O T decreases heat chemical heat

Endothermic vs. Exothermic • Exothermic H 2 O T increases heat chemical heat

Endothermic vs. Exothermic • Graphs of Potential Energy – Endothermic Products PE E in Reactants Reaction Coordinate Note: Chemical E increasing

Endothermic vs. Exothermic • Graphs of Potential Energy – Exothermic Reactants PE E out Products Reaction Coordinate Note: Chemical E decreasing

Endothermic vs. Exothermic DH = Molar Heat 1. H represents: PE (heat content) of products or reactants a. k. a. “enthalpy”

Endothermic vs. Exothermic 2. DH is the change in heat content DH = Hproducts – Hreactants (Find DH 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.