2. • How many moles of liquid water must freeze
to remove 100 kJ of heat? (Hf = 334 J/g)
3. Know Values
• Q=
• Hf=334j/g
• Molar mass of water=18g/mole
• Do we need to convert?
• Equations – how do we solve?
4. Convert?
• How many moles of liquid water must freeze
to remove 100 kJ of heat? (Hf = 334 J/g)
• YES, Q is given in kJ and Hf is in joules
• So convert 100kJ to joules
• There are a 1000 joules per kilojoule so
• 100kJ x 1000j/kJ 100,000 j
5. Solving us Hf
• First find out how many grams by using
Hf=joules of heat/grams of ice
• Rearrange first
• Grams of ice=Joules of heat/Hf
• Grams of ice =100,000j/334j/g
• Divide (joules cancel)
• =299.4 grams
6. How many moles?
• 18 g/mole or 1mole/18 g
• We have 299.4 grams
• 299.4gx 1mole/18g (grams cancel)
• =16.6 moles of water
