Section 2.4 Chemical Reactions • Chemical reactions change substances into different substances by breaking and forming bonds. • Chemical reactions are responsible for all the actions of organisms. – Examples • Photosynthesis • Respiration (breathing) • Digestion • Metabolism is all the chemical reactions in an organism • Reactants are changed in a reaction • EXAMPLE: • Oxygen+Sugars (Reactants) • Products are formed in a reaction CO2 + Water (Products) Activation Energy: energy required to start a reaction. Two Types of Reactions Exothermic • Energy EXITS! • The prefix “exo-” means “out” • Example: – respiration Endothermic • • • Energy goes IN! The prefix “Endo” means “into” Example: - photosynthesis Vocabulary Check 1. Making and breaking chemical bonds are examples of ____________. 2. Bonds are broken in the ______, which are the chemicals that are changed during the process. 3. Bonds are made in the ________, which are the chemicals that result from the process. Vocabulary Check cont… 1. The ________ is the amount of energy needed to start a reaction. 2. If a reaction absorbs more energy than it releases, it is called an __________ reaction. 3. If a reaction releases more energy than it absorbs, it is called an __________ reaction. Endo or Exo? 1. Which is the solute, which is the solvent? 2. Reactants and Products? 3. 2H2O2 2H2O + O2 • 4. How are exothermic and endothermic reactions different? • Exothermic or endothermic? Exothermic or endothermic? Exothermic or Endothermic?