Energy changes in reactions
Enthalpy: A measure of the internal energy (Ep) of the reactants or products
Enthalpy: Symbol = H
Enthalpy of reaction: Heat of reaction
Enthalpy of reaction: Symbol = ΔH (kg/mol)
Heat of reaction
= The net change in chemical potential energy of the system
= (The system is all chemicals involved in the reaction)
Temperature of a substance: The average kinetic energy of the composing particles
Exothermic
Temperature increased
Therefore, average Ek increased
Thus, Ep decreased
= ΔH < 0 (negative)
Endothermic
Temperature decreased
Therefore, average Ek decreased
Thus, Ep increased
= ΔH > 0 (positive)
Exothermic: Chemical potential energy is transformed into thermal energy
ΔH < 0
Echemp Ek
Endothermic: Thermal energy is transformed into chemical potential energy
ΔH > 0
Ek Echemp
Activation energy: Ea
The minimum energy required to start a chemical reaction.
Colliding molecules must have the kinetic energy equal to or larger than the Ea in order to react.
Activated complex:
A high energy, unstable, temporary transition state between the reactants and the products.
Energy is absorbed when bonds or forces are broken.
Energy is released when bonds or forces are formed.
Enthalpy: A measure of the internal energy (Ep) of the reactants or products
Enthalpy: Symbol = H
Enthalpy of reaction: Heat of reaction
Enthalpy of reaction: Symbol = ΔH (kg/mol)
Heat of reaction
= The net change in chemical potential energy of the system
= (The system is all chemicals involved in the reaction)
Temperature of a substance: The average kinetic energy of the composing particles
Exothermic
Temperature increased
Therefore, average Ek increased
Thus, Ep decreased
= ΔH < 0 (negative)
Endothermic
Temperature decreased
Therefore, average Ek decreased
Thus, Ep increased
= ΔH > 0 (positive)
Exothermic: Chemical potential energy is transformed into thermal energy
ΔH < 0
Echemp Ek
Endothermic: Thermal energy is transformed into chemical potential energy
ΔH > 0
Ek Echemp
Activation energy: Ea
The minimum energy required to start a chemical reaction.
Colliding molecules must have the kinetic energy equal to or larger than the Ea in order to react.
Activated complex:
A high energy, unstable, temporary transition state between the reactants and the products.
Energy is absorbed when bonds or forces are broken.
Energy is released when bonds or forces are formed.
