Endothermic and exothermic reactions
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Endothermic and exothermic reactions. Teacher : Claudia De Candido Tutor: Elena Monti ITC “O.Mattiussi” 2005/06. Menu. Exothermic and endothermic reactions. Experiments: hot pack and cold pack. Questions about observing and comparing. Energy level diagrams.

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Endothermic and exothermic reactions

Endothermic and exothermic reactions

Teacher : Claudia De Candido

Tutor: Elena Monti

ITC “O.Mattiussi” 2005/06


Menu

  • Exothermic and endothermic reactions.

  • Experiments: hot pack and cold pack.

  • Questions about observing and comparing.

  • Energy level diagrams.

  • Quick test, crosswords, fill in the blanks.


Objectives
Objectives

  • In this unit the students will:

  • identify endothermic or exothermic processes through temperature changes;

  • learn about the energy level diagrams and the difference in energy between products and reactants;

  • understand the meaning of the E positive or negative;

  • make predictions about reactions, known the energy level diagrams or E.


Skills
Skills

  • Knowledge of the new words and the new concepts.

  • Accurate explanation of energy level diagrams.

  • Prediction of behaviour through the acquainted knowledge.

  • Grade Level : second classes - secondary school.


Evaluation
Evaluation

  • During the lessons the students can evaluate their understanding and their improvements through activities single or in group.

  • Assessment:

  • fill in the blanks,

  • speaking (questions),

  • quick test,

  • matching exercise.


Time

  • 4 class periods 50 min. each.


Suggestions
Suggestions

  • What the students need to do:

    • Ask, ask, ask if you don’t understand.

    • During the experiments follow instructions carefully.

    • Take notes and take part in the lessons.

    • Practice and revise even when we don’t tell you.


Procedures
Procedures

  • Before showing the menu and the objectives, performing some reactions and give students a puzzle to discover the topic.

  • Perform some experiments using hot packs and cold packs. The students can hold these systems in their hands to see and feel that the reaction takes place.

  • Introduce the concept of endo/exothermic processes showing slides.

  • Repeat the experiments with chemicals , measuring the temperature. The students will make notes and answer the questions.

  • Ask the students to give examples of different kinds of exothermic processes (combustion, explosions ) and endothermic processes (melting ice , photosynthesis).

  • Introduce the energy diagrams for both of reaction and discuss the energy of reactants and products, the convention used to write the heat taken in and given out.

  • Summarise all the features of these reactions.

  • Do exercises and gather the worksheets.


Resources required
Resources required

  • Hot pack and cold pack, ammonium nitrate, calcium chloride, water.

  • Thermometer, beaker, stick.

  • Projector, computer, power point presentation about exothermic and endothermic reactions.


Safety
Safety

  • Wear chemical splash goggles and gloves to prepare the solutions.


Exo and endothermic reactions
Exo and endothermic reactions

  • Exothermic reactions release heat energy to the surroundings.

  • Endothermic reactions absorb heat energy from the surroundings.


Cold and hot packs
Cold and hot packs

  • How do instant hot and cold packs work?


Hot pack
Hot pack

  • Pressing the bottom , the diaphragm breaks.

  • Calcium chloride dissolves in water and warms it.

  • The beverage gets warm.


Exothermic process
Exothermic process

  • Heat flows into the surroundings from the system in an exothermic process.

Energy

Surroundings

Hot pack

Temperature rises


Hot pack1
Hot pack

  • We will repeat the process in a beaker with calcium chloride ( 25 g CaCl2) + water (25 ml) and a thermometer.

  • We will record the initial temperature of the water and the temperature after the dissolution of the salt.

  • Observation:

  • a temperature rise of…….


Cold pack
Cold pack

  • Water and ammonium nitrate are kept in separate compartments.

  • Pressing the wrapper, the ammonium nitrate dissolves in water and absorbs heat.

  • The pack becomes cold.

It is used to treat

sports injuries.


Endothermic process
Endothermic process

  • Heat flows into the system from the surroundings in an endothermic process.

Surroundings

Cold pack

Energy

Temperature falls


Cold pack1
Cold pack

  • We will repeat the process in a beaker with ammonium nitrate ( 25 g NH4NO3) + water (25 ml) and a thermometer.

  • We will record the initial temperature of the water and the temperature after the dissolution of the salt.

  • Observation:

  • a temperature drop of…….


Students worksheet
Students’ worksheet

  • Fill in the blanks


Complete the sentences below observing your system and using the correct word
Complete the sentences below observing your system and using the correct word.

  • The system is similar to ………………(hot /cold pack)

  • The salt which dissolves in water is……………

  • The heat energy is ……………………..(given off/ taken in)

  • The temperature ………………. (falls/rises). In fact the initial temperature was ……..and the final temperature is……………

  • The reactions is ………………….. (endothermic/exothermic)


Question
Question using the correct word.

  • What exothermic reactions or endothermic reactions do you know?


Changes of state
Changes of state using the correct word.

Liquid Vapor

requires energy.

This is the reason:

a) you cool down after swimming

b) you use water to put out a fire.

+ energy


Explosions
Explosions using the correct word.

This reaction is exothermic!


Photosyntesis
Photosyntesis using the correct word.

This reaction is endothermic!


Combustions
Combustions using the correct word.

These reactions are exothermic!


Changes in physical state
Changes in physical state using the correct word.


Giving reasons
Giving reasons using the correct word.

  • Why does the system give off or take in heat energy?


Energy level diagrams
Energy Level Diagrams using the correct word.

Endothermic reactions

products

energy

energy taken in

is positive

reactants

The products are higher in energy than the reactants

time of reaction



Energy level diagrams1
Energy Level Diagrams using the correct word.

Exothermic reactions

Energy given out

is negative

reactants

energy

products

Time of reaction

The products are lower in energy than the reactants



Ca Cl using the correct word.2 (s) Ca Cl2 (aq)

Ca Cl2 (s)

Heat

E <0

Heat given off is negative

energy

Ca Cl2 (aq)


Heat using the correct word.

energy

E = - 812 kJ/mol

Heat given off is negative


NH using the correct word.4NO3 (s)

NH4NO3 (aq)

NH4NO3 (aq)

Heat

energy

E>0

Heat absorbed is positive

NH4NO3 (s)


Heat using the correct word.

energy

E = + 68 kJ/mol

Heat absorbed is positive


Exothermic reactions
Exothermic reactions using the correct word.

  • The products have less energy than the reactants.

  • The energy is given out to the surroundings.

  • Ep - Er = E <O

  • The temperature goes up.


Endothermic reactions
Endothermic reactions using the correct word.

  • The products have more energy than the reactants.

  • The energy is taken in from surroundings.

  • Ep - Er = E >O

  • The temperature goes down.


Direction energy
Direction energy using the correct word.

  • Every energy measurement has three parts:

  • a unit ( Joules of calories);

  • a number how many;

  • a sign to tell direction (negative – exothermic, positive- endothermic).


Crossword
Crossword using the correct word.

Across

3. Able to burn

7. The electrical attractive force between the atoms

9. Substance that changes in a reaction

10. Specific part of the universe that is of interest in the study.

11. Ammonium nitrate and calcium chloride

12. The burning of fuels

13. The new substances in a reaction

Down

1. A reaction which absorbs energy

2. It increases in an exothermic reaction

4. A reaction which releases energy

5. Energy that is absorbed or released during a chemical reaction

6. This is the main endothermic plant process in nature

8. Chemical change


Heat pads
Heat pads using the correct word.

  • A heat pad contains a solution which exists as a liquid at a temperature minor than the melting point. Bending a metal disk inside the crystallisation process starts. The heat of the solidification is given out.

  • The supercooled solution is sodium acetate and water.

  • Boiling the solid, you melt it back to the liquid state.


Head packs
Head packs using the correct word.


Glossary
Glossary using the correct word.


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