Endothermic and Exothermic Reactions Quiz

Endothermic and Exothermic Reactions

• Chemical reactions involve energy release or absorption. Energy can take forms like heat, light, or electricity.
• Energy in reactions comes from breaking existing bonds (requiring energy input) and forming new bonds (releasing energy).
• Reactions can be classified as endothermic or exothermic based on energy transfer.

Endothermic Reactions

• Require energy input (heat) to proceed.
• Absorb heat from surroundings.
• Feel cold to the touch, because heat is being absorbed in the process.
• Example: liquid ice packs (reaction with water and ammonium nitrate), photosynthesis.

Exothermic Reactions

• Release energy (heat) during the process.
• Give off heat.
• Feel warm or hot to the touch, because heat is being released.
• Example: burning of wood, explosion of dynamite, rusting

Overall Energy Changes in Reactions

• In endothermic reactions, the energy needed to break existing bonds is greater than the energy released when new bonds are formed.
• In exothermic reactions, the energy released when forming new bonds is greater than the energy taken in to break existing bonds.

Reaction Profile Diagrams

• Show the energy changes during a chemical reaction.
• The difference between reactants and products, on a reaction profile graph, is the energy change in the reaction.
• The diagram shows the progress of the reaction.

Activation Energy

• The minimum amount of energy required to start a chemical reaction.
• Without this energy, a reaction won't happen.
• Examples:
  • Striking a match requires enough energy to start combustion.
  • Gasoline requires a spark (enough energy input) to burn in air.

Catalysts

• Substances that speed up chemical reactions without being used up in the process.
• Catalysts reduce the activation energy (the required minimum energy to start the reaction), so less energy is needed to get the reaction going.
• Examples: Enzymes are biological catalysts.