{ exothermic & endothermic reactions energy in reactions
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Exothermic & Endothermic REACTIONS
Energy in Reactions
Some chemical reactions release heat to the surroundings
• These are called EXOTHERMIC reactions• Heat EXITS the reaction
Some chemical reactions absorb heat from the surroundings
• These are called ENDOTHERMIC reactions• Heat ENTERS the reaction
Energy in Reactions
All substances have a type of chemical potential: • The total energy (J or kJ) contained in a system • Chemical potential energy in a substance• The symbol for enthalpy is H• ΔH = Hproducts – Hreactants
Energy in Reactions
An exothermic reaction converts the enthalpy stored in a substance into HEAT which is released to the surroundings
N2 + 3H2 2 NH3+ heat
Exothermic Reactions
Has higher enthalpy
Has lower enthalpy
Exothermic Enthalpy Diagram
Products
ReactantsEnthalpy (H)
Reaction Proceeds
H is ΔNegative
1. The “heat term” written on the PRODUCTS side
N2 + 3H2 2 NH3 + 46.2 kJ
2. ΔH written beside the equation is NEGATIVE.
N2 + 3H2 2 NH3 ΔH = - 46.2 kJ
Exothermic Reactions
Exothermic Reactions:• ΔH is negative• Products are lower than reactants on the
enthalpy diagram• Heat is released to the surroundings
In Summary…
An endothermic reaction absorbs heat from the surroundings and converts into enthalpy
2C + 2 H2 + heat C2H4
Endothermic Reactions
Has higher enthalpy
Has lower enthalpy
Endothermic Enthalpy Diagram
ΔH is POSITIVE
Products
Reactants
Enthalpy (H)
Reaction Proceeds
1. The “heat term” written on the REACTANTS side.
2 C + 2H2 + 52.3 kJ C2H4
2. ΔH written beside the equation is POSITIVE.
2 C + 2 H2 C2H4 ΔH = + 52.3 kJ
Endothermic Reactions
Endothermic Reactions:• ΔH is positive• Products are higher than reactants on the
enthalpy diagram• Heat is absorbed from the surroundings
In Summary…
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