Key Concepts

The process of dissolving deserve to be endothermic (temperature goes down) or exothermic (temperature walk up).When water dissolves a substance, the water molecule attract and “bond” to the particles (molecules or ions) the the substance leading to the corpuscle to separate from each other. The “bond” the a water molecule makes is not a covalent or ionic bond. The is a solid attraction caused by water’s polarity.It takes energy to break the bonds in between the molecules or ion of the solute. Power is released when water molecules bond come the solute molecules or ions.If it takes much more energy to separate the particles of the solute 보다 is released when the water molecules bond to the particles, then the temperature goes under (endothermic). If the takes less energy to separate the corpuscle of the solute than is released as soon as the water molecules bond to the particles, climate the temperature goes up (exothermic).


Students will certainly feel the temperature adjust that occurs as soon as a cold pack and a hot pack room activated. They will check out that these temperature alters are as result of a solid problem dissolving in water. Students will then compare the temperature alters that happen as four different solutes dissolve in water and classify these together either endothermic or exothermic. Students will certainly be presented to the concept that it takes energy to break bonds and also energy is released when bonds are formed during the process of dissolving.


Students will have the ability to identify variables in an experiment to discover out exactly how much the temperature increases or decreases as each of four solutes dissolves in water. Student will have the ability to correctly share the procedure of dissolving as either exothermic or endothermic because that each solute. Students will have the ability to explain that the temperature alters in dissolving room a result of the amount of power released compared to the lot of energy used as “bonds” room formed and broken.

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Download the student task sheet, and also distribute one per student as soon as specified in the activity. The task sheet will serve as the “Evaluate” ingredient of every 5-E class plan.


Be certain you and the student wear properly fitting goggles. Overabundance dry product from the hot and cold packs can be placed in the trash.

Materials because that the Demonstrations

2 disposable cold packs2 disposable warm packsGraduated cylinderWater (room temperature)2 clear plastic cups2 thermometers

Materials because that Each Group

Potassium chlorideCalcium chlorideSodium carbonateSodium bicarbonateWater5 little cupsGraduated cylinderThermometerGram balance

Notes about the Materials

The hand warmer shown in the video in the Extend includes a super-saturated equipment of salt acetate through a small metal disk within a clean plastic bag. This warmer is activated by bending the metal disk slightly. This hand warmers, referred to as The warm Solution, are available from Flinn Scientific, product number AP1933, and also a selection of various other vendors. Potassium chloride may be purchased in ~ a grocery store under the brand surname Nu-Salt Salt instead of or native Flinn Scientific, product number P0042.Calcium chloride may be purchased at a hardware keep under the brand surname Damp-Rid or stimulate calcium chloride, anhydrous product number C0016 indigenous Flinn Scientific.Sodium carbonate, anhydrous might be purchased from Flinn Scientific, product number S0052. Sodium bicarbonate is baking soda. That may likewise be purchased from Flinn Scientific, product number S0043.

Read an ext about the energy transforms in making and also breaking bonds in the context of dissolve in the teacher background section.

Note: This task deals v a concept that is not frequently addressed in center school—that a temperature adjust occurs throughout the process of dissolving. Most center school textbooks and also curricula associate a readjust in temperature just with chemical change. Dissolve is usually thought about a physical adjust but also can an outcome in a readjust in temperature. This readjust in temperature is based upon the energy changes connected in breaking and making “bonds” in the process of dissolving.


Allow student to feeling the temperature adjust in an triggered cold pack and an activated hot pack.

Tell students that they will check out how part hot and cold packs work. Offer them a hint that it has to do with dissolving, i m sorry they have actually been studying in this chapter.

Materials because that the Demonstration

1 disposable cold pack1 disposable hot pack


Select 2 student volunteers—one come activate one cold pack and also another come activate one hot pack. Have actually each student feeling each bag and also guess what is inside each. Castle should notice a dried pellet-like solid and a fluid-filled bag. Allude out that the bags do not feeling cold or hot yet.

Direct the students come activate your packs by following the instructions on the package. Have them shake the packs to get the liquid to spread throughout the bag.

Pass the cold and hot packs roughly the room.

Expected outcomes

The cold pack quickly becomes cold while the hot pack easily becomes hot.

Do a demonstrate to show how cold and hot packs work.

Note: In this demonstration, 1 teaspoon of every substance is liquified in 10 mL that water. Due to the fact that the function of this demonstrate is to show whether the temperature simply goes up or down, this type of volume measure is fine. But to compare which problem is much more or less exothermic or endothermic 보다 another, together students will do in the activity, the solute will be measure in grams.

Materials for the Demonstration

1 disposable cold pack1 disposable warm packGraduated cylinder, 50 mL or smallerWater (room temperature)2 clear plastic cups2 thermometers1 teaspoon


Carefully cut open one cold pack and one warm pack. Present students the contents, yet do not handle or permit students to take care of the heavy substance inside the packs. Phone call students that the liquid within the fluid-filled bags in both the cold and hot packs is water. Pour around 10 mL that room-temperature water in two separate clear plastic cups. Ar a thermometer in every cup and select two student volunteer to call the course the starting temperature that the water in every cup.

With the thermometer still in the cup, add around 1 teaspoon of the solid substance from the cold load to the water in one cup. Gently swirl the cup to aid the substance dissolve. Have actually the course watch the thermometer and then ask a student to phone call the class the lowest temperature of the solution.

With the thermometer still in the cup, place about 1 teaspoon of the substance from the warm pack in the water in the other cup. Gently swirl the cup to aid the problem dissolve. Have the course watch the thermometer and then asking a college student to phone call the course the greatest temperature that the solution.

Expected Results

Dissolving the substance from the cold load will cause the temperature come decrease to less than 10 °C (endothermic). Dissolving the substance from the hot pack will reason the temperature to rise to over 40 °C (exothermic). Results may vary.

Introduce the state endothermic and exothermic.

Tell students the scientists describe temperature transforms that happen when substances interact as either endothermic or exothermic. Once the temperature decreases, together it does in the cold pack, the procedure is endothermic. Once the temperature increases, together it does in the warm pack, the procedure is exothermic.


Introduce the dissolving activity students will execute and help students identify the variables.

Tell students that they will compare exactly how much the temperature changes when four household substances dissolve in water. Present the crystals students will dissolve:

Potassium chloride is a typical salt substitute.Calcium chloride is used to absorb humidity from the air. It is also included in some ice-melt mixtures to act icy sidewalks during winter. Sodium carbonate is a typical ingredient in detergents because that dishwashing machines.

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Have students monitor alters in temperature together they dissolve four different household solutes in water.

Question come Investigate

Which solute dissolves the many endothermically and also which dissolves the many exothermically in water?

Materials for Each Group

Potassium chlorideCalcium chlorideSodium carbonateSodium bicarbonateWater5 small cupsPermanent marker or masking tape and also penGraduated cylinderThermometerGram balance


Label the tiny plastic cup Potassium Chloride, Calcium chloride, sodium carbonate, and also Sodium bicarbonate.Weigh 2 g of every solute and place castle in their labeled cups. Include 10 mL that water to the tiny unlabeled cup and place a thermometer in the water. Document this early stage temperature in the graph on the task sheet.

Pour the potassium chloride into the water and swirl the cup. Clock the thermometer.

When the temperature stops changing, record the final temperature. Repeat procedures 3–5 for each solute.

Expected Results

Potassium chloride dissolved the most endothermically, and also calcium chloride liquified the many exothermically. College student temperature readings will certainly vary, however will likely be similar to the following:

Discuss college student observations.

Ask students:

Which solutes dissolved endothermically? Potassium chloride and also sodium bicarbonateWhich solute liquified the many endothermically?Potassium chlorideWhich solutes dissolved exothermically?Calcium chloride and sodium carbonateWhich solute dissolved the many exothermically?Calcium chloride