Energy Changes in Chemical Reactions

Definitions

closed chemical system - closed system containing only reactants and products

chemical thermodynamics - study of energy changes in chemical systems

enthalpy - a measure of the internal energy of the system

activated complex - unstable transition state from reactants to products

reactants - a starting material in a chemical reaction

products - a substance formed in a chemical reaction

exothermic reaction - energy (in the form of heat and light) is released in a chemical reaction

endothermic - energy is absorbed in a chemical reaction

activation energy - minimum energy required to get a reaction to start

enthalpy change - amount of heat energy absorbed or released in a chemical reaction

Enthalpy

• a chem. system holds energy in the energy of the bonds and kinetic energy of molecules and atoms

enthalpy change

• energy absorbed or released in a chemical reaction

Exothermic reactions

• negative resultant energy

• gives off energy

Endothermic reactions

• absorb energy

• positive resultant energy

Chemical Bonds and Bond Energy

• when a bond is formed → energy released to surroundings

• when a bond is broken → energy taken in from surroundings

  bond energy

  • energy taken in or given out when a mole of bonds broken

Activation Energy

• minimum energy required for a reaction to take place

reactants → activated complex → product

• very short amount of time, energy in system at maximum