1. Heat and Change of State Thornburg 2014

2. When an ice cube melts, it absorbs heat from its surroundings. The liquid water holds a temperature of 0 ˚ C until all of the ice has melted into liquid water Only once the ice cube has entirely melted does the liquid water begin to change temperature This occurs because it takes work (energy) to actually convert the solid into liquid This “work” is what chemists call the Heat of Fusion Thornburg 2014

3. Phase Change and Energy Thornburg 2014

4. Chemists measure the amount of energy required to convert 1 mole of a substance as its… Molar heat of vaporization (liquid → gas) Molar heat of condensation (gas → liquid) Molar heat of solidification (liquid → solid) Molar heat of fusion (solid → liquid) Thornburg 2014

5. Practice Problem The Molar Heat of fusion for water is… ∆H fus H 2 O = 6.01 KJ/mole Calculate the amount of heat absorbed when 200 g of ice (H 2 O) at 0 ˚ C melts and turns into liquid water at 0 ˚ C. 200 g of H 2 O x 1 mole H 2 O x 6.01 KJ = 18 g of H 2 O 1 mole H 2 O 66.8KJ Thornburg 2014