Latent heat of vaporization of water experiment
Answers
Answer:
Here is a simple experiment that can be performed in almost any laboratory.� No expensive or special equipment is required in order to obtain relatively accurate results.
This procedure has been performed in our freshmen chemistry laboratories for many years with excellent results.� The experiment is useful in enumerating several important basic chemistry concepts.� These concepts include the following:
1. The effect of external pressure upon boiling point is easily illustrated1.� One can show that as the pressure inside of the boiling flask is reduced, the boiling point is lowered.� Starting with the lowest pressure that can be obtained by using a good aspirator, a dynamic demonstration is presented. One can hold their hand for an indefinite period of time on the surface of the boiling flask while the water is boiling.
2. This experiment provides an excellent opportunity to introduce the concept of logarithms to the freshmen students.� Many students have scientific calculators that have logarithm functions; yet, they are totally unaware of the purpose of these keys.
3. This experiment can be used to help students to develop new techniques in the preparation of graphs.� In connection with this, the concept of reading slopes and the meaning of the slope intercept form of an equation for a straight line, should become apparent following successful completion of the experiment.
4. If computers are available, this experiment provides an excellent opportunity to use a spreadsheet program to perform a regressional analysis.� Ultimately, the task can be performed using an appropriate scientific calculator.� The slope of the best-fit line is provided either by the spreadsheet calculations or the calculator.
5. This experiment provides an avenue to discuss evaporation and vaporization. Factors including temperature and intermolecular forces that influence equilibrium vapor pressure can be explained.� The definition of boiling can be explained relative to the vapor pressure of a liquid and the external pressure applied to that liquid.� Finally, students are exposed to experimental technique wherein a value, in this case the heat or vaporization of water, is obtained indirectly by measuring other quantities.
6. If an aspirator is used to develop the required vacuum, its operation can be illustrated and explained.� Contrary to popular belief, most aspirators do not operate upon Bernoulli�s principle where streamline flow is expected2.� Please refer to figure III.
Answer:
Because we allowed the 5 mL sample of water to completely vaporize, we can divide the energy absorbed by this sample by the mass of the sample in order to determine the heat of vaporization of water (in Joules per gram). We can compare this experimental value to the accepted value of 40.7 kJ/mol (2260 J/g).