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Chapter 5, Lesson 9 Multimedia

Breaking and Making Bonds

This video shows that breaking bonds requires energy, while making bonds releases energy.

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  • When two atoms or molecules that are attracted to each other are together, it takes energy to break them apart.
  • When two atoms or molecules that are attracted to each other are apart, energy is released when they form a bond.
  • It takes energy to break bonds and energy is released when bonds are formed.

Energy and Dissolving

Energy is released as water molecules associate with solute particles. Energy is absorbed when solute molecules are seperated from one another by the water molecules.

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  • When water molecules are attracted to and bond to the solute, energy is released.
  • It takes energy When water molecules pull on the solute, causing it to separate.

Exothermic Dissolving

The process of dissolving a solute in water.  Two solute molcules are first surrounded by water molecules. In an exothermic dissolving process, when the water molecules associate with the solute particles, energy is released.  More energy is released when the water molecules associate with the solute particles than is abosrbed when water molecules

If more energy is released when water bonds to the solute than it takes to separate the solute, the dissolving is exothermic and the temperature increases.

Endothermic Dissolving

The process of endothermic dissolving in water.  Two solute molcules are first surrounded by water molecules. In an endothermic dissolving process, when the water molecules associate with the solute particles, not much energy is released.  More energy is required to pull the solute molecules apart than is released when the water moleclules first as

If less energy is released when water molecules bond to the solute than it takes to separate the solute, the dissolving is endothermic and the temperature decreases.

Hand Warmer

A hand warmer is activated and a crystal forms, along with a drastic increase in temperature.

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  • The liquid in the hand warmer is a very concentrated solution of a salt called sodium acetate.
  • The sodium and acetate ions are ready to bond with each other and with water molecules to form a crystal.
  • Then these ions and molecules attract and bond to each other, energy is released.

Temperature Change Alcohol in Water

A small sample of rubbing alcohol is added to a cup of water. The mixture briefly appears very cloudy, then clears up.

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  • When alcohol dissolves in water, water molecules “bond” to alcohol molecules and separate them from other alcohol molecules.
  • The energy released when alcohol and water molecules attract and bond is greater than the energy required to separate alcohol molecules from each other.
  • Since the energy released is greater than the energy absorbed, the dissolving of alcohol in water is exothermic.