Measuring the Latent Heat of Fusion

The "calorimeter" is an insulated container which (hopefully) does not allow heat to enter or escape. It therefore allows us to measure the latent heat of fusion of water by melting ice in water: the heat gained by the ice in melting is lost by the water, and its final temperature will reflect this loss.

We will use a calorimeter, a balance, a beaker, a thermometer, water, ice and a hot pad.

Name:

Lab Partners:

When entering numeric data, use exponentials: ie., 1.6 * 10-19 = 1.6E-19.

Procedure

  1. Measure the mass of the inner calorimeter cup (without the ring) and the stirrer:
    mcup & stirrer = g
    Record the temperature of the room air:
    Tair = C

  2. Fill the beaker with enough water to fill the inner cup half way, and heat it to a temperature 10-15 degrees C above room temperature.

  3. Fill the inner cup half way with the heated water and weigh it with the stirrer to determine the mass of the water:
    mcup & stirrer & water = g
    Place the cup and stirrer into the calorimeter jacket. Stir the water gently and measure the temperature of the water:
    Tstart = C

  4. Select several small pieces of ice (about the size of the end of your thumb,) and dry them carefully with paper towel. Without touching them with your fingers, add them to the water, being careful not to spill any water. Gently stir the water. When the ice has melted, read the temperature of the water.

  5. Repeat step 4 until the temperature is lower than room temperature by the same amount that it was higher in step 3. Record the final temperature:
    Tfinal = C
    Why do we stop when we do?

  6. Weigh the inner cup, water and stirrer to determine the mass of the ice added:
    mcup & stirrer & water & ice = g

Analysis

  1. The cup and stirrer are made of aluminum. Look up the specific heat of aluminum:
    cAl = cal / g C

  2. Compute the heat capacity (specific heat times mass) of the cup and stirrer:
    Ccup & stirrer = cAl * mcup & stirrer

    = cal / C

    and that of the water:
    Cwater = cH2 O * ( mcup & stirrer & water - mcup & stirrer )

    = cal / C

    and that of the melted ice:
    Cmelted ice = cH2 O * ( mcup & stirrer & water & ice - mcup & stirrer & water )

    = cal / C

  3. Compute the heat lost by the cup and stirrer and the water:
    DQcup & stirrer & water = ( Ccup & stirrer + Cwater ) * ( Tstart - Tfinal )

    = cal

    Subtract from that the heat gained by the melted ice:
    DQ = DQcup & stirrer & water - Cmelted ice * ( Tfinal - 0 )

    = cal

    This assumes that the entire apparatus plus contents is at equilibrium both before and after the ice has melted, and that the ice was at 0 C before it was added.

  4. Divide the result of the last step by the mass of the ice:
    L = DQ / ( mcup & stirrer & water & ice - mcup & stirrer & water )

    = cal / g

    and calculate the error in that amount relative to the accepted value for the latent heat of fusion of water:
    DL = 100 % * | L - 80 | / 80

    = %

©2004, Kenneth R. Koehler. All Rights Reserved. This document may be freely reproduced provided that this copyright notice is included.

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