Endothermic/Exothermic Processes

Fall 2013 Vanderbilt Student Volunteers for Science

Training Presentation

Important!!!

• Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit!

• We recommend that you work through the kit with your team prior to going into the classroom.

• This presentation does not contain the entire lesson—only selected experiments that may be difficult to visualize and/or understand.

I. Introduction and Set-Up

• One team member should fill plastic water bottles with water when you arrive. Another team member should put the following vocabulary words on the board:endothermic exothermic chemical changepotassium chloride physical changeanhydrous calcium chloride

• Other team members can divide the materials in the box for the various activities.

• Divide students into pairs.• Take time to explain “endothermic” and “exothermic”. See manual

for detailed discussion.

II. Endothermic Physical Processes

• Give each pair the following:– 1 styrofoam cup– 1 thermometer– a 50 mL graduated cylinder – one water bottle (shared by two pairs)– 2 observation sheets– 1 instruction sheet in sheet protector

• Distribute 8 4 oz jars of potassium chloride with 8 plastic spoons so they can be shared by two pairs of students.

• Tell each PAIR that one of the students should fill the graduated cylinder to the 50 mL mark with water and add it to the Styrofoam cup.

• The other student should measure the temperature of the water by placing the thermometer in the water.

• Record the temperature on the observation sheet.

• One of the students should add two spoonfuls of potassium chloride and stir carefully with the thermometer.

• Record the lowest temperature reached on the observation sheet. (Takes several minutes so students have to keep watching).

III. Exothermic Physical Processes • Recyclable Hand-Warmer - Show the class

a recyclable hand warmer that contains a supersaturated sodium acetate solution.

• Distribute 8 hand warmers to every other pair - tell students to share among two pairs.

• One student in each group should use a finger tip to firmly bend the metal activation disc.

• Students should see white solid beginning to form around the disc. If they don’t, they need to bend the metal activation disc again.

• Point out that the hand warmer can be recycled by placing it in a pan of hot water for several minutes.

• Ask the students to explain how the recyclable hand warmer illustrates the law of conservation of energy. Energy is added when the solution is heated to form the supersaturated solution (liquid), and energy is released when crystallization occurs.

• WHEN FINISHED, COLLECT ALL HAND WARMERS AND RETURN TO THE KIT BOX

IV. Exothermic Chemical Processes

Part A: Starting Chemical (HotHands) Hand Warmer

• Distribute the 8 HotHands hand warmers to every other pair and tell students to share among two pairs.

• Have one of the students tear open the plastic covering, take out the hand warmer and have group members note that it is at room temperature.

• Then shake it, and put it aside until Part B.

• Students should also save the plastic covering.

• NOTE: The directions on the plastic covering suggest waiting 30 minutes, but students will be able to feel warmth from the hand warmer after about ten minutes.

• HAVE STUDENTS GO ON TO PART B WHILE THEY ARE WAITING FOR HAND WARMERS TO GET WARM.

IV. Exothermic Chemical Processes (cont.)

Part B. Anhydrous calcium chloride mixed with water

• Give each pair another Styrofoam cup • Distribute 8 4-oz jars of anhydrous calcium

chloride with 8 plastic spoons so they can be shared by two pairs.

• Have pairs do the following:– Add 50 mL of water to a styrofoam cup.– Place a thermometer in the cup, and

after a few minutes, record the temperature of the water.

– Add one plastic spoonful of anhydrous calcium chloride to the styrofoam cup and stir carefully with the thermometer.

• Record the highest reading reached. This will take several minutes. (Students should observe an increase of about 20 degrees C, so this is an exothermic reaction.)

• Disposal: Pour the solutions from the Styrofoam cups into the waste bottle provided. Put used styrofoam cups in the trash bag before putting them back in the kit box. Also put the waste bottle back in white plastic bag with water bottles.

IV. Exothermic Chemical Processes (cont.)

• Part C. Checking the HotHands Hand Warmer

• Tell the class that the “missing ingredient” that is needed to make the hand warmer warm up is oxygen. When the plastic covering is removed, the inside pouch is porous enough to allow air to enter the pouch. The oxygen in air reacts with iron to form iron oxide with the release of heat. The HotHands hand warmer is an exothermic chemical reaction that occurs when powdered iron is mixed with activated carbon, water, salt, and vermiculite in the presence of air.

• Take the empty 4 oz jar, cut open a hand warmer pouch and pour the contents inside the jar. Let the students look at this jar and compare what the contents look like with the jar that contains contents of a HotHands hand warmer that were exposed to air for 24 hours.

• Ask students to record their observations on the observation sheet and to indicate whether a chemical or physical change has occurred.