Energy Level Diagrams and Enthalpy Changes
This page introduces fundamental concepts in energetics, focusing on energy level diagrams and various types of enthalpy changes.
Energy level diagrams are used to visualize the energy changes in chemical reactions. These diagrams show the activation energy, overall energy change, and whether a reaction is exothermic or endothermic.
Definition: Enthalpy is the energy stored in chemical bonds.
Exothermic and endothermic reactions are differentiated based on their energy changes:
Example: Exothermic reactions, such as acid reacting with hydrogencarbonate, release energy to the surroundings, causing the temperature to increase.
Example: Endothermic reactions, like thermal decomposition, absorb energy from the surroundings, resulting in a temperature decrease.
The concept of activation energy is introduced:
Definition: Activation energy is the minimum energy that particles must possess to collide and react, measured in kJ mol^-1.
Standard enthalpy changes are defined under specific conditions:
Highlight: Standard conditions are defined as 100 kPa pressure, 298 K temperature, and 1 mol dm^-3 concentration.
Various types of standard enthalpy changes are explained:
- Standard enthalpy change of reaction
- Standard enthalpy change of formation
- Standard enthalpy change of combustion
- Standard enthalpy change of neutralization
Vocabulary: Standard enthalpy change of formation ΔHf° is the enthalpy change associated with forming 1 mole of a compound from its elements under standard conditions, with all substances in their standard states.
