May/June 2017 – Vol. 29 No. 7

Energy in Chemical Reactions Lab

Posted: Friday, October 1st, 2010

by Jeff Bradbury and Patricia Buchanan

Name ____________________

Date _____________________

Partner’s Name_____________

Question: Food provides us with energy to live, but how much of this energy can actually be found in a single peanut?

Purpose: To determine the heat of a chemical reaction.

Part 1 Introduction

Background Information:

1.       What is a calorie?

A Calorie is a unit of heat.  It is the amount of heat needed to raise the temperature of 1 gram of water 1 degree Celsius.  You will actually measure the calories of a food product and compare this to the calories on the container.  Food Calories usually have an upper case C.  1 Calorie = 1000 calories.  Today you will measure calories and then convert them to Calories.

2.       How are heat and temperature different?

Temperature is the average amount of kinetic energy contained in the molecules of a substance.  It is measured with a thermometer and the units are degrees Celsius.  Heat is the total amount of energy in a sample of substance.  It is measured indirectly and the units are calories.

3.       How is heat measured?

To measure calories in food, for example, the food is burned in a combustion chamber.  The heat from the combustion reaction of the food is used to raise the temperature of a sample of water.  Knowing the mass of the water and the temperature change of the water the heat gained by the water can be calculated using the following equation:

M X C X ΔT = Heat change in the water (q)

M is the mass of the water.  Δ T is the final temperature of the water—the initial temperature of the water (Δ T means change in temperature).  C is a constant called specific heat.  It tells how a particular substance absorbs heat.  All substances absorb heat differently.  It takes one calorie of heat to raise the temperature of one gram of water one degree Celsius.  C for water is 1 cal/g oC.

Example:

125 grams of water are heated by burning a sample of sugar.  The temperature of the water goes from 21 oC to 76 oC.  How much heat did the water absorb?  How much heat did the sugar release?

Answer Absorbed:____________________ Released: ____________________

SAFETY!

Safety goggles must be worn at all times.  Be careful when lighting a burner.

Part 2 Procedure

Procedure, Observations, and Data:

In this lab you will be working in groups of two.

1. Measure the mass of the apparatus, which is a wire that is attached to a cork

2. Place 1/2 of a peanut on the apparatus and find the mass.

3. Put exactly 25 ml of water in a 100 ml beaker.  Measure and record the temperature of the water.

4. Light the peanut on fire with a Bunsen burner, and once the peanut is lit, quickly hold the beaker of water over the peanut.  The goal is to get as much heat into the water as possible.  (Is it possible to get all of the heat into the water?)

5. Do not let the water boil!  Blow out the flame before this happens.

6. After the peanut has burned, make sure the water is mixed so that the hot water is evenly dispersed in the beaker, and measure the temperature of the water and record.

7. Record the mass of the apparatus and peanut after it was burned.  Be sure to pick up any crumbs that fell off of the wire.

8. Repeat this experiment until you have burned two peanuts.

Table 1:  Mass and Temperature Changes in a Chemical Reaction

Mass of apparatus Mass of apparatus and peanut (initial) Mass of apparatus and peanut (final) Temperature of water (initial) Temperature of water (final) Mass of water used

Part 3 Calculations (Do this for each peanut)

Show all of the calculations for one nut in your lab book but show the results of all calculations in a table in your book

1. What is the initial mass of the peanut?

2. What is the final mass of the peanut?

3. What is the change in mass of the peanut?

4. What is the change in temperature of the water?

5. What is the heat gain of the water in calories?

6. What is the heat gain of the water in Calories?

7. What is the experimental heat loss of the peanut in Calories?

8. What is the heat loss per gram of the peanut?

9. What is the average heat loss per gram of the peanut?

10. What is the theoretical heat loss per gram of the peanut in Calories? (from the average)

11. What is the efficiency of this experiment? (from the average)

Table 2:  Calculating Heat Changes in a Chemical Reaction

Initial mass of peanut Final mass of peanut Change in mass of peanut Change in temp. of water Heat gain of water cal. Heat gain of water Cal. Experimental heat loss of peanut in Cal. Experimental heat loss per gram of peanut in Cal. Ave. heat loss of peanut Theo. heat loss of peanut % Eff.

Questions:

1. How could you make it so that more of the heat from the burning peanut goes into the water

2. The mass of the peanut went down and the temperature of the water went up.  Did you change matter into energy?  Make sure you explain your answer with evidence.

3. What happened to the matter of the peanut that was burned?

4. How did the energy get into the peanut in the first place?

Jeff Bradbury is a Professor of Chemistry at Cerritos College in Norwalk; Patricia Buchanan is the Cal Grip Grant Project Assistant at Cerritos College.  The original idea for this activity came from the Los Angeles County Office of Education 15 years ago, which the authors modified.

Written by California Science Teachers Association

California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

One Response

  1. As a chemistry teacher of 30 years I have to say that with the number of students who have peanut allergies these days this lab has been modified by most of us to use other food sources from cheerios to cheetos but ANYTHING except NUTS
    If a kid is allergic and inhales the smoke from the peanut he will end in the hospital
    The questions on this lab are well thought out but PLEASE change the food source!
    It can also be done simply and easily with candles as the FUEL if you are not talking food energy but rather alternative fuels along with ethanol–just a few drops in a dish.
    I use an aluminum can to hold over the flame with a ring stand adn can even build an insulating chinmey

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