MHS AP Chemistry
Heat of Fusion of Ice

Purpose
In this lab you will calculate the energy required to change one gram of ice to water at its melting point (0 °C).  This is also the energy that must be removed from one gram of water at its freezing to point to change it ice.  This quantity is known as "the Specific Heat of Fusion of Ice," and has the symbol  DHf.

Materials
lots of ice                calorimeter

Procedure
Let the tap water run hot for a few minutes to get the hottest possible water coming out.  Record the mass of the empty calorimeter cup, and the mass of the same cup with about 200 mL of hot water in it.  Place a thermometer in the cup and wait until the temperature steadies.

Obtain about 50 g of ice.  That's about 1/2 a handful.  Make sure it has a minimal coating of water from melting.

Record the temperature of the hot water immediately before adding the ice.  Record the temperature every five seconds until it has been constant for 25 sec.  What is the final temperature?

Measure the final mass of the mixture and cup.

Data

 T of ice water (°C) __________ __________ __________ V of hot water (mL) __________ __________ __________ T of hot water (°C) __________ __________ __________ Final V of water mix (mL) __________ __________ __________ Final T of water mix (°C) __________ __________ __________

Calculations & Results

 m of water mix (g) __________ __________ __________ m of hot water (g) __________ __________ __________ mass of ice (g) __________ __________ __________ DT hot water (C°) __________ __________ __________ DT melted ice (C°) __________ __________ __________ Cp water (cal/gC°) __________ __________ __________ DHf ice (cal/g) __________ __________ __________ Avg DHf ice (cal/g) __________ % error (%) __________ __________ __________

Hints
Remember that the heat gained or lost by a substance that changes temperature (but not phase) can be found by the formula

q = mCpDT
where m is the mass of the substance, Cp is its heat capacity, and DT is the change in temperature.  The heat capacity of water is  1 cal/gC°.

When a substance changes state, there is an energy change, but instead of a change in temperature, the molecules change their positions relative to each other (this is a potential energy change).  The energy change for this is calculated by

q = mDHpc
where “pc” stands for the phase change being examined.  Notice there is no DT term in this formula.

Use the formula  qmelt + qwarm up + qcool down = 0 to calculate the heat of fusion of water in cal/g.  Compare to the book's value (seee p. 385; it’s in kJ/mole so you may have to convert).  This TOTAL energy change is zero because all the energy in water to start with is still there at the end.

Be careful to show all labels and calculations!