Chapter 5, Lesson 9 Multimedia

Breaking and Making Bonds

• 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

• 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

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

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

• 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

• 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.