Heat & Enthalpy - Jan. 12

In today's lesson we learned about Heat, Enthalpy, and the reactions.

-Reactions that release heat are exothermic. (Hot)
-Reactions that absorb heat are endothermic. (Cold)
-Heat is a form of energy
-All chemicals have energy stored in them
-Stored chemical energy is called enthalpy

Enthalpy of Gasoline > Enthalpy of Water







- Enthalpy has a symbol H
- Change in enthalpy is:






Enthalpy Diagrams (Exothermic & Endothermic)
Exothermic
- H is negative
- Products are lower than reactants
- Heat is released

Endothermic
- H is positive
- Reactants are lower than products
- Heat is absorbed




Two ways to write enthalpy in reactions













- Coefficients can stand for moles or molecules








1 mole of N2 produces 46.3 kJ
3 mole of H2 produces 46.3 kJ
2 mole of NH3 produces 46.3 kJ

This gives conversion factors:
46.3 kJ/ 1 mol N2
46.3 kJ/ 3 mol H2
46.3 kJ/ 2 mol NH3


Ex. Find the amount of heat released if 7.0 mol of N2 are consumed.
46.3 kJ/ 1 mol N2 x 7.0 mol of N2 = 324.1 kJ