What Type Of Reaction Involves A Net Increase In Energy?

Are you loving this? Not loving this? Delight consider taking a moment to share your feedback with us. Thanks!

Lesson vi.7

Energy Changes in Chemic Reactions

Key Concepts

If 2 substances react and the temperature of the mixture decreases, the reaction is endothermic.
If two substances react and the temperature of the mixture increases, the reaction is exothermic.
A chemic reaction involves the breaking of bonds in the reactants and the forming of bonds in the products.
Information technology takes energy to break bonds.
Energy is released when bonds are formed.
If a reaction is endothermic, information technology takes more energy to pause the bonds of the reactants than is released when the bonds of the products are formed.
If a reaction is exothermic, more energy is released when the bonds of the products are formed than it takes to intermission the bonds of the reactants.

Summary

Students will conduct two chemical reactions. In the first, the temperature volition go downwardly (endothermic) and in the second, the temperature will become up (exothermic). Students will see an animation to review a concept that was introduced in Chapter five—that it takes energy to break bonds and that energy is released when new bonds are formed. Students will apply this idea to explain why a reaction is either endothermic or exothermic.

Objective

Students volition be able to define an endothermic and exothermic reaction. Students will be able to use the concept of energy in bond breaking and bond making to explain why one reaction can exist endothermic and another reaction can be exothermic.

Evaluation

Download the student action sheet, and distribute one per student when specified in the action. The activity sail will serve equally the "Evaluate" component of each 5-Eastward lesson plan.

Rubber

Exist sure y'all and the students article of clothing properly fitting goggles.

Materials for Each Group

Vinegar
Blistering soda
Calcium chloride
H2o
Thermometer
4 small cups
Disposable self-heating hand warmer
Self-inflating airship

Additional Materials if Yous Cull to do the Actress Extend

Magnesium sulfate
Sodium carbonate
Citric acid
Universal indicator

About the Materials

Calcium chloride is available from Sargent Welch, Production #WLC94075-06, or Flinn Scientific, Product #C0016, or other suppliers. Calcium chloride is also available in hardware stores for absorbing wet and for melting ice in the winter.

Hand warmers may be purchased from Flinn Scientific, itemize #AP1931 or from camping ground, sporting goods, or discount stores. Look for hand warmers that are disposable and sealed in a package and will merely warm up when the packet is opened. Self-inflating mylar balloons may be purchased from Joissu, product number #43-712 or Educational Innovations, product #AS-800.

Hash out the temperature changes in chemical reactions students have conducted and so far.

Remind students that the decomposition reaction of hydrogen peroxide and the reaction with copper II sulfate and aluminum both acquired the temperature of the solution to increase. Tell students that you lot volition show them three chemic reactions where the temperature increases dramatically.

Project the video Thermite Reaction.

Afterwards adding one or more catalysts, iron oxide (rust) and aluminum react to produce elemental iron and aluminum oxide. And then much heat is produced in this reaction that the iron becomes a liquid. The heat is so intense that the molten atomic number 26 tin can exist used to weld railroad tracks together.

Project the video Nitrogen Triiodide Reaction.

This is a decomposition reaction where nitrogen triiodide decomposes into nitrogen gas and purple iodine vapor. Nitrogen triiodide crystals are so unstable that just a light touch will crusade them to rapidly decompose generating a cracking deal of heat.

Projection the video White Phosphorous Reaction.

White phosphorous is dissolved in a solvent and spread on a piece of paper. When the solvent evaporates, the phosphorous reacts with oxygen in the air in a combustion reaction.

Ask students to make a prediction:

Do you recall substances can react and cause the temperature of the mixture to subtract?

Tell students that this lesson is going to explore temperature changes in chemic reactions.

Give Each Student an Activeness Sheet.

Students will tape their observations and reply questions about the activity on the activeness sheet. The Explicate It with Atoms & Molecules and Take Information technology Further sections of the activity sail will either exist completed as a class, in groups, or individually, depending on your instructions. Await at the teacher version of the activeness sheet to find the questions and answers.
Take students measure the change in temperature of the reaction between baking soda and vinegar.

Question to Investigate

Does the temperature increase, decrease, or stay the same in the reaction between baking soda and vinegar?

Materials
- Vinegar in a cup
- Baking soda in a loving cup
- Thermometer
Materials Note: The amount of the solutions must be plenty to cover the seedling of the thermometer. If they aren't, use a smaller cup or clip the finish of a plastic-backed thermometer so that the backing is flush with the bottom of the bulb.

Teacher Preparation
- Place well-nigh 10 mL of vinegar in a modest plastic cup for each group.
- Place about ½ teaspoon of baking soda in a small cup for each group.
Procedure
1. Place a thermometer in the vinegar. Read the thermometer and tape the temperature on the activity sheet.
2. While the thermometer is in the cup, add together all of the baking soda from your cup.
3. Sentry the thermometer to observe any change in temperature. Record the temperature after it has stopped changing.
Expected Results

If you begin with room-temperature vinegar, the temperature will decrease by nearly vii °C. The amount of temperature subtract will vary. Carbon dioxide gas is likewise produced.
Discuss student observations.

Ask students:

Did the temperature increase, subtract, or stay the same when yous combined blistering soda and vinegar?

The temperature decreased.

What is the lowest temperature reached during your group's reaction?

There volition likely be some variation.

Tell students that when the temperature of a chemic reaction decreases, the reaction is called an endothermic reaction. The first part of the give-and-take, endo, means in or into and thermic has to do with heat or energy. And then an endothermic reaction means that more energy goes into making the reaction happen than is released by the reaction. This leaves the reaction mixture at a lower temperature.
Have students measure out the change in temperature of the reaction betwixt blistering soda solution and calcium chloride.

Question to Investigate

Does the temperature increment, subtract, or stay the aforementioned in the reaction between blistering soda solution and calcium chloride?

Materials
- Baking soda solution in a loving cup
- Calcium chloride in a cup
- Thermometer
Teacher Grooming
- Make a baking soda solution past dissolving about 2 tablespoons of baking soda in 1 cup of water. Stir until no more blistering soda will dissolve.
- Identify almost x mL of baking soda solution in a small plastic cup for each group.
- Place most ½ teaspoon of calcium chloride in a small loving cup for each group.
Procedure
1. Place a thermometer in the baking soda solution. Read the thermometer and tape the temperature on the activeness canvas.
2. While the thermometer is in the cup, add all of the calcium chloride from the cup.
3. Watch the thermometer to detect any change in temperature. Record the temperature when it stops irresolute.
Expected Results

The temperature of the solution should increase by about 15–xx °C. The temperature increase volition vary. Carbon dioxide gas is produced, and a white cloudy precipitate, calcium carbonate, is formed.

Read more about exothermic and endothermic chemic reactions in the teacher background section.

Annotation: Some of the temperature increment in this reaction may be due to the chemic reaction between blistering soda and calcium chloride, simply some is too due to the exothermic fashion calcium chloride dissolves in water. Chapter five Lesson ix addresses temperature changes every bit bonds between a solute are broken and the bonds between the solute and water are formed during the physical change of dissolving.
Discuss pupil observations.

Ask students:

Did the temperature increase, decrease, or stay the same when yous combined baking soda solution and calcium chloride?

The temperature increased.

What is the highest temperature reached during your group's reaction?

In that location will likely be some variation.

Tell students that when the temperature of a chemical reaction increases, the reaction is called an exothermic reaction. The get-go part of the word, exo, means out or out of, and thermic has to do with heat or energy. So an exothermic reaction means that more free energy goes out or is released by the reaction than goes into it. This leaves the reaction mixture at a higher temperature.
Explain how differences in the energy required to intermission bonds and make bonds cause temperature changes during chemical reactions.

Tell students that an example of a very exothermic reaction is the combustion or burning of fuel like the gas in a kitchen stove. Even if students have seen the animation of the combustion of methyl hydride from Affiliate half dozen, Lesson 1, remind them that methane (CH₄) reacts with oxygen (O₂) from the air to produce carbon dioxide gas (CO_ii) and h2o vapor (H₂O) and a lot of energy.

Project the animation Methyl hydride Combustion Free energy.

Click on the marsh gas and the oxygen to show that it takes energy to interruption the bonds of the reactants. This is shown by "energy arrows" going into the molecules of the reactants. Then click on the carbon dioxide and the water to show that free energy is released when the atoms bail to make the products. This shown past the energy arrows coming out of the molecules in the products. Show students that more energy was released when the bonds in the products were formed than was used to break the bonds of the reactants. This is shown past larger energy arrows coming out of the products and smaller energy arrows going into the reactants. Since more free energy was released than was used, this reaction gets warmer and is exothermic.

Project the image Blistering Soda and Calcium Chloride Reaction.

Ask students:

Is this an endothermic or exothermic reaction?

Exothermic.

What exercise yous know well-nigh the amount of free energy required to break the bonds of the reactants compared to the amount of energy required to class the products?

More than energy was released when the bonds in the products were formed than was required to pause the bonds in the reactants.

If nosotros were using energy arrows, where would the bigger and smaller arrows go?

A smaller arrow going in would be on the reactant side and a bigger arrow coming out would exist on the product side.

Project the epitome Blistering Soda and Vinegar Reaction.

Ask students:

Is this an endothermic or exothermic reaction?

Endothermic.

What do you know about the amount of free energy required to break the bonds of the reactants compared to the amount of energy released when the products are formed?

More energy was released when the bonds in the products were formed than it took to break the bonds in the reactants.

If we were using energy arrows, where would the bigger and smaller arrows become?

It took more energy to suspension the bonds of the reactants than was released when the bonds in the products were formed.

Project the blitheness Endothermic Reaction.

Remind students that a chemical reaction involves the breaking of bonds in the reactants and the making of bonds in the products. Likewise remind them that it takes free energy to intermission bonds and that energy is released when bonds are formed.

In an endothermic reaction, it takes more energy to break the bonds of the reactants than is released when the bonds in the products are formed. In an endothermic reaction, the temperature goes down.

Projection the animation Exothermic Reaction.

Explain that in an exothermic reaction it takes less energy to break the bonds of the reactants than is released when the bonds in the products are formed. In an exothermic reaction, the temperature goes upwardly.
Have students explain how changes in energy during chemic reactions cause them to be either endothermic or exothermic.

Tell students that they will utilize their knowledge of endothermic and exothermic reactions to draw the energy changes that occur when paw warmers and cocky-inflating balloons are activated. These two different products utilise chemical reactions to make them work.

Materials for Each Grouping
- Disposable self-heating manus warmer
- Self-inflating balloon
Hand Warmer

Tell students that the outer packaging on the paw warmer keeps air away from it and prevents the chemical reaction from happening, until the moment when a consumer wants it to start producing rut. Oxygen in the air is 1 of the reactants in the chemical reaction. So once the package is opened, the iron pulverisation in the hand warmer reacts with the oxygen in the air.

Cocky-Inflating Balloon

Tell students that the chemic reaction that causes the cocky-inflating balloon to inflate is very similar to a chemical reaction students accept explored already. Take students gently feel the self-inflating balloon to guess what the reactants are. They should discover a tablet and a sealed package of liquid inside the balloon. Explain that the tablet is baking soda and the liquid in the packet is citric acid, which reacts with baking soda in a way similar to vinegar. The sealed packet prevents the citric acrid from reacting with the baking soda.

Process
1. Open the bundle the hand warmer is in to begin the chemical reaction.
2. Shake the paw warmer and feel for any temperature modify.
3. Activate the cocky-inflating balloon by either pressing downwards or stepping on the bundle of citric acid to rupture it.
4. Shake the balloon and feel the area on the balloon where the liquid is.
5. Be certain everyone in your group has a take a chance to feel both the hand-warmer and the self-inflating balloon.
Expected Results

The hand warmer will become warmer, and the liquid in the self-inflating balloon will go colder. The airship will inflate as carbon dioxide gas is produced.

Enquire students:

Which is an example of an endothermic reaction? An exothermic reaction?

The self-inflating airship is an instance of an endothermic reaction, and the paw warmer is an example of an exothermic reaction.

What tin can you say near the corporeality of energy required to interruption bonds in the reactants compared to the amount of free energy that is released when bonds are formed in the products in the cocky-inflating balloon?

In the self-inflating balloon, more energy is required to break the bonds in the reactants than is released when the new bonds in the products are formed. Therefore, the reaction is endothermic.

What tin you lot say about the amount of free energy required to break bonds in the reactants compared to the corporeality of energy that is released when bonds are formed in the products in the hand warmer?

In the mitt warmer, more energy is released when the new bonds in the products are formed than is used to break the bonds in the reactants. Therefore, the reaction is exothermic.

What practice yous recall is the gas inside the self-inflating balloon?

Carbon dioxide gas is produced when citric acid and baking soda react.

If you practice not have admission to a self-inflating balloon, you may choose to have students brand their own.

Materials for Each Group
- Alka-Seltzer tablet
- H2o
- Graduated cylinder
- Snack size zip-closing plastic purse
Process
1. Identify 10 mL of water in a nothing-endmost plastic bag.
2. Tilt the open bag at an angle so that the water flows into 1 corner. Hold the bag while a partner places the Alka-Seltzer tablet in the opposite corner. Remove equally much air as possible and seal the handbag.
3. Shake the purse to aid water and tablet react. Place the handbag in a bowl or other container in case it pops.
4. Feel the liquid about the tablet to come across if there is any temperature alter.
Expected Results

The liquid volition get colder and the bag will inflate and may pop.
Have students identify clues of chemical change in the following reactions.

Remind students that in this affiliate, they accept seen unlike clues of chemical change. Ask students to identify all of the clues they find in this pair of chemical reactions.

Question to Investigate

What clues practice you find that a chemic reaction is taking identify?

Materials for Each Group
- Magnesium sulfate solution in cup
- Sodium carbonate solution in loving cup
- Citric acrid solution in cup
- Universal indicator
- Thermometer
- Dropper
Instructor Preparation
- Label three small-scale cups Magnesium Sulfate, Sodium Carbonate, and Citric Acid for each group.
- Brand each solution by adding:
  - i tablespoon of magnesium sulfate to 250 mL of h2o.
  - i teaspoon of sodium carbonate to 125 mL of water.
  - ane teaspoon of citric acid to 125 mL water.
- Cascade 30 mL of magnesium sulfate, ten mL of sodium carbonate, and 10 mL of citric acrid solution into their labeled cups for each grouping.
Procedure
1. Add five drops of universal indicator to the magnesium sulfate solution.
2. Identify a thermometer in the loving cup and record the temperature of the solution.
3. Add 10 mL of sodium carbonate solution.
4. Add together 10 mL of citric acid.
Expected Results

The magnesium sulfate, universal indicator, and sodium carbonate volition turn regal and grade a precipitate. With the addition of citric acid, the mixture volition plough xanthous or pink and bubble as the precipitate disappears. There is no noticeable temperature alter.

Ask Students:

What clues do you lot find that let yous know that a chemical reaction is taking place?

There is a color change, formation of a precipitate, another color change, and bubbling.

How can it be that in this chemic reaction, you lot did not find a temperature change?

Maybe the amount of free energy required to pause bonds was about the aforementioned as the corporeality of energy released when bonds are formed. Or the temperature change was so pocket-sized that information technology was non noticeable with student thermometers.