When a material undergoes a phase transition from one state to another -- solid to liquid, liquid to gas, solid to gas -- it may release or absorb large amount of energy. Today, you will practice your skills in calorimetry by measuring
Your lab manual describes the procedure by which you can measure the heat given off by a chunk of ice as it melts. Basically, you place an ice cube into an insulated cup of a known masss of water at a known temperature, let the cube melt completely, let the ice-water come to equilibrium with the original water, and then measure the temperature of the resulting mixture.
How close is your value of the latent heat of fusion of ice to the value in your textbook? Did your modifications lead to a better result in the second trial?
Calculating the uncertainty in your value for latent heat of fusion is tough: there are several steps in the calculation, some of them additive and some multiplicative. You need to use different rules for combining uncertainties in the two different kinds of steps. You can do it, but it will take ten or fifteen minutes. Ask me for help if you don't know what to do.
Once you have a value for the uncertainty, you can check to see if your latent heat of fusion agrees with the textbook's value within the uncertainty.
As a challenge, try a very similar experiment using a piece of solid carbon dioxide instead of ice. Solid CO2 will not melt into a liquid; instead, it will sublimate into a gas. Can you use the same apparatus to measure this procedure? Let's find out.
Follow the same procedure as you did for ordinary ice. Watch carefully for signs that gas is escaping from your calorimeter. Is there anything you can do to stop it from doing so?
You may use this value for the latent heat of sublimation of C02:
246.3 BTU/lbOne BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. Convert this value to Joules per kilogram before you compare it to the value you determined experimentally.
How close is your value of the latent heat of sublimation of CO2 to the value above?
You should hand in all your work before you leave the lab room. In addition to the items specified above, it should include
Last modified May 16, 2001 by MWR.
Copyright © Michael Richmond. This work is licensed under a Creative Commons License.