thermochemistry

• collision theory: bonds are broken and/or formed when reactant particles collide with enough energy and correct orientation
• activated complex: an unstable cluster of atoms that exists during the transition from reactants to products
• system: part of the universe in which you focus your attention
• heat: energy that moves from one object to another due to a temperature difference

  • transfer of energy occurs during a collision or through radiation
  • heat always flows from warmer object to cooler object
• during any chemical or physical process, the energy of the universe remains the same. if the energy in the system increases/decreases, it is absorbed or released into its surroundings
• enthalpy change (ΔH): amount of heat transferred between the system and its surroundings at constant pressure
• endothermic reaction: absorbs energy as heat; positive enthalpy change
• exothermic reaction: releases energy as heat; negative enthalpy change
• internal energy is the total energy of the particles in a system, including the kinetic and potential energies

  • change in internal energy is the sum of heat absorbed and any work done on the system minus the sum of heat released and any work done by the system
• bond enthalpy: the amount of energy needed to break the bonds of any one mole of a substance
• enthalpy diagram: a representation of the relative enthalpy of a system undergoing a chemical change
• enthalpy of reaction: the energy change when one mole of a substance is formed or broken in a chemical reaction
• activation energy: the minimum energy that colliding particles must have in order to react
• thermochemical equation: an enthalpy change represented in a chemical equation
• a phase change occurs when adding or removing heat changes how the particles are arranged in a substance
• molar enthalpy of fusion: enthalpy change when 1 mole of a substance is formed from its gaseous state
• molar enthalpy of solidification is the enthalpy change when 1 mole of a solid is formed from its gaseous state
• molar enthalpy of vaporization is the enthalpy change when 1 mole of a liquid is formed from its gaseous state
• molar enthalpy of condensation is the enthalpy change when 1 mole of a gas is formed from its liquid state