```Measuring the Heat Energy of a Chemical ChangePatricia Riley                 Lincoln Park High School                               2001 N. Orchard St. Mall                               Chicago IL 60614                               (312) 534-8130Objectives:

To compare the heat conducting properties of water and paper by boiling water.
To study the Law of Conservation of Energy.
To study the differences between heat and temperature.
To calculate the heat produced by a burning candle.
To calculate the heat produced by a burning nut.
To compare the heat produced by equal masses of different types of nuts.

Materials needed:

Teacher's demonstration:        Equipment per group of 4:
1 ring stand                    thermometer           test tube
1 small ring clamp              candle                test tube holder
paper cups                      petri dish            large cork
goggles                         matches               disposable lighter
apron                           water                 various nuts
balance

Strategy:

1.  Fit a paper nut cup into the ring clamp, attach the clamp to the ring stand,
fill the cup to the brim with water, and place a candle under the cup.  Ask the
students to make predictions as to what will happen when the candle is lighted.
Light the candle.  On the chalk board record the observations.  In a separate
column record the questions this experiment raises among the students.  In a
third column list possible answers (hypotheses) suggested by the students for
their questions.  Where ever possible test the hypotheses with a brief
experiment.  Have the students draw a conclusion:  the cup does not burn because
the water removes the heat from the paper before the paper becomes hot enough
to burn.
2.  Now investigate how much heat is produced by the candle.  Explain that a
calorie is a unit of heat.  Ask students what they know about calories; most
will say that foods contain calories, exercise burns calories, and calories can be counted.  Emphasize that a candle burns wax and air to release calories of energy (heat and light), just as our body burns food, though without a flame, to release energy (heat, muscle energy, etc.).  Have the students work in groups and:     a.  First attach the candle to a petri dish.  Then weigh the dish and candle on a balance.     b.  Measure 10mL of water into a graduated cylinder and then pour into a test tube.     c.  Take the temperature of the water.     d.  Use a test tube holder to hold the test tube.  Light the candle.  Hold the test tube in the flame, while gently moving the test tube in small circles.     e.  Continue heating for two or three minutes.  Take the temperature of the water just before removing the test tube from the flame.  Be sure the thermometer does not touch the glass as its read.     f.  Blow out the candle.  Weigh the candle and the petri dish.     g.  Record all observations:  water temperature before heating, the water temperature after heating, volume of water heated, mass of candle and dish before heating, mass of candle and dish after burning, mass of candle burned.     h.  Record also any questions raised by the group during the experiment.     i.  Calculate the heat produced by the burning candle:          Heat produced = Heat absorbed =  Mass of X  Temperature X  1 cal
by candle       by water         water      change of       g x oC                                                      water     j.  Calculate the heat produced by one gram of candle:          Heat produced by one gram = Heat produced by burning candle = cal/g                                       Mass of candle burned     k.  Pool the class data on the board.  Discuss the questions the students raised in their groups.  Students should draw conclusions:  even though the groups all burned different masses of candle, they all came up with the same number of calories per gram (cal/g).3. Now consider whether all substances that burn produce the same amount of heat per gram burned.  Students may say that foods do not all contain the same number of calories.  Have the students again work in their groups to explore this by repeating step 2 for three varieties of nuts (suggested:  Brazil, peanuts, walnuts; be sure they are raw, not roasted).  A nut is stuck onto a dissecting pin (already inserted into a cork).  Burn the nut instead of the candle.  Ignite the nut with a disposable lighter.  Heat the test tube of water until the nut stops burning.  Record all data and questions raised.  Pool class data.  Draw conclusions:  all varieties of nuts do not produce equal amounts of energy.References:

Schug, Ken.  Demonstration given during S.M.I.L.E., Fall, 1992.
Summerlin, Lee R. and Ealy, James L., Jr.  Chemical Demonstrations:  a Source
Book for Teachers, Volume I.  American Chemical Society, Washington, D.C.,     1988.```