How many joules does it take to melt 35 g of ice at 0° C?
It takes 12,000 Joules of energy to melt 35 grams of ice at 0 °C
The enthalpy change for melting ice is called the entlaphy of fusion. Its value is 6.02 kj/mol. This means for every mole of ice we melt we must apply 6.02 kj of heat. We can calculate the heat needed with the following equation:
In this problem we would like to calculate the heat needed to melt 35 grams of ice at 0 °C. This problem can be broken into three steps:
1. Calculate moles of water
2. multiply by the enthalpy of fusion
3. Convert kJ to J
Step 1: Calculating moles of water
Step 2: Multiply by enthalpy of fusion
Step 3: Convert kJ to J
Finally rounding to 2 sig figs (since 34°C has two sig figs) we get
For more examples on phase changes and enthalpy, see the video below:
One last note, if the temperature were not 0 °C then the ice would have to be heated in addition to melted. This would be a phase change problem combined with a heat capacity problem.