Unit 6 DNF AP CHEM

Made by Alexie Dayrit

What are the characteristics of exothermic (exo) and endothermic (endo) reactions in terms of ΔH, heat, and temperature?

Exothermic reaction (exo):
ΔH < 0 (−) Feels hot Heat is a product Temperature goes up Endothermic reaction (endo): ΔH > 0 (+)
Feels cold
Heat is a reactant
Temperature goes down

What is the bond energy relationship in breaking and forming bonds for endothermic and exothermic reactions?
 

Breaking bonds is endothermic (requires energy).
Forming bonds is exothermic (releases energy).

How is ΔH calculated for a reaction?

ΔHrxn = ΔHproducts − ΔHreactants or ΔHrxn = ΔHreactants − ΔHproducts

4:
 Question: If a reaction is exothermic or endothermic, how does that relate to the strength of the bonds formed in the products compared to the reactants?

 Answer: In an exothermic reaction, the bonds formed in the products are stronger than in the reactants. In an endothermic reaction, the bonds formed in the products are weaker than in the reactants.

5:
 Question: What happens to ΔH when you double a reaction?

 Answer: Doubling a reaction multiplies ΔH by 2.

6:
 Question: What happens to ΔH when you reverse a reaction?
 

Answer: Reversing a reaction changes the sign of ΔH (if it was exothermic, it becomes endothermic, and vice versa).

7:
 Question: What happens to ΔH when you add multiple reactions together?

 Answer: When adding reactions, ΔH values are summed (ΔH = ΔH1 + ΔH