Exothermic or Endothermic?

 

Background: A process is described as endothermic when heat energy is absorbed, increasing the internal energy of the system. If you touch a container that holds an endothermic process, it will feel cool to touch. An exothermic process results when heat energy is released, decreasing the internal energy of the system. If you touch a container that holds an exothermic process, it will feel warm or hot to the touch. In order for a reaction to occur, the particles involved must have enough energy to break the existing bonds to form new bonds. The minimum energy required for a chemical reaction is called the activation energy. When more energy is released as products form than is absorbed to break the bonds in the reactions, the reaction is exothermic. When more energy is needed to break the bonds in the reactants than is given off by forming the bonds in the products, the reaction is endothermic.

 

Purpose: Students will be able to:

1. Identify exothermic and endothermic reactions
2. Observe the formation of products from reactants
3. Observe and provide activation energy to start reactions

 

Materials:

-plastic baggies                                                    -8 g ammonium thiocyanate

-1 g ammonium nitrate                                         -flasks

-water                                                                     -rubber stopper

-5g Sodium carbonate/ Calcium Chloride         -wood panel

-sodium hydroxide pellets                                  -test tube

-digital balance                                                     -graduated cylinder

 

Procedure: Part One

1)       Place 1 g of ammonium nitrate in a resealable plastic bag.

2)       Add 5 mL of water to the bag and seal.

3)       Record your observations in Table A. Was the reaction endothermic or exothermic?

 

Procedure: Part Two

1)       Place 5 g of Sodium Carbonate/Calcium Chloride to a resealable plastic bag.

2)       Add 5 mL of water to the bag.

3)       Record your observations in Table A. Was the reaction endothermic or exothermic?

 

Procedure: Part Three

1)       To a flask containing 8 g of Ammonium Thiocyanate, add 16 g of barium hydroxide.

2)       Place a rubber stopper in the mouth of the flask. Shake it vigorously.

3)       Place the stoppered flask on a wood board that has been wet down with puddles of water.

4)       Record your observations in Table A. Was the reaction endothermic or exothermic?

 

Procedure: Part Four

1)       Using a chemical scoop, transfer 3 pellets of sodium hydroxide to a test tube half full of water. **Attention: do not pick up sodium hydroxide with your hands. It will burn you! Wear goggles when adding the sodium hydroxide to the water!**

2)       Carefully feel the side of the test tube.

3)       Record your observations in Table A. Was the reaction endothermic or exothermic?

 

 

 

Data: Table A

 

Procedures	Brief Description of Procedure	Endothermic/Exothermic Reaction?
Procedure 1
Procedure 2
Procedure 3
Procedure 4

 

Questions/Analysis: Answer the questions below in complete sentences.

 

1) What reactions were endothermic?

 

 

 

2) How could you tell the reactions were endothermic?

 

 

 

3) What reactions were exothermic?

 

 

 

4) How could you tell the reactions were exothermic?

 

 

 

5) Identify the following changes as exothermic or endothermic:

 

a)       Melting ice:          

b)       Lighting a match:

c)       Frying an egg:

 

6) The water in a teapot is heated on a stovetop. The water begins to boil. Where is the activation energy coming from in this reaction?

 

 

 

 

7) The water in a teapot is heated on a stovetop. The temperature of the water increases. Is this an endothermic or exothermic reaction? Why?