1. { Exothermic & Endothermic REACTIONS Energy in Reactions

2. Some chemical reactions release heat to the surroundings These are called EXOTHERMIC reactions These are called EXOTHERMIC reactions Heat EXITS the reaction Heat EXITS the reaction Some chemical reactions absorb heat from the surroundings These are called ENDOTHERMIC reactions These are called ENDOTHERMIC reactions Heat ENTERS the reaction Heat ENTERS the reaction Energy in Reactions

3. All substances have a type of chemical potential: The total energy (J or kJ) contained in a system The total energy (J or kJ) contained in a system Chemical potential energy in a substance Chemical potential energy in a substance The symbol for enthalpy is H The symbol for enthalpy is H ΔH = H products – H reactants ΔH = H products – H reactants Energy in Reactions

4. An exothermic reaction converts the enthalpy stored in a substance into HEAT which is released to the surroundings N 2 + 3H 2  2 NH 3 + heat Exothermic Reactions Has higher enthalpy Has lower enthalpy

5. Exothermic Enthalpy Diagram Products Reactants Enthalpy (H) Reaction Proceeds ΔH is Negative

6. 1. The “heat term” written on the PRODUCTS side N 2 + 3H 2  2 NH 3 + 46.2 kJ 2. ΔH written beside the equation is NEGATIVE. N 2 + 3H 2  2 NH 3 ΔH = - 46.2 kJ Exothermic Reactions

7. Exothermic Reactions: ΔH is negative ΔH is negative Products are lower than reactants on the enthalpy diagram Products are lower than reactants on the enthalpy diagram Heat is released to the surroundings Heat is released to the surroundings In Summary…

8. An endothermic reaction absorbs heat from the surroundings and converts into enthalpy 2C + 2 H 2 + heat  C 2 H 4 Endothermic Reactions Has higher enthalpy Has lower enthalpy

9. Endothermic Enthalpy Diagram ΔH is POSITIVE Products Reactants Enthalpy (H) Reaction Proceeds

10. 1. The “heat term” written on the REACTANTS side. 2 C + 2H 2 + 52.3 kJ  C 2 H 4 2. ΔH written beside the equation is POSITIVE. 2 C + 2 H 2  C 2 H 4 ΔH = + 52.3 kJ Endothermic Reactions

11. Endothermic Reactions: ΔH is positive ΔH is positive Products are higher than reactants on the enthalpy diagram Products are higher than reactants on the enthalpy diagram Heat is absorbed from the surroundings Heat is absorbed from the surroundings In Summary…

14. In Class Work  Please collect the Endo/Exo Worksheet from the front of the room, finish this worksheet by next class  Next Class: Begin Stoich