1 Endothermic and exothermic reactions Teacher : Claudia De Candido Tutor: Elena Monti ITC “O.Mattiussi” 2005/06

2 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.

3 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.

4 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.

5 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.

6 Time 4 class periods 50 min. each.

7 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.

8 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.

9 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.

10 Safety Wear chemical splash goggles and gloves to prepare the solutions.

11 Exo and endothermic reactions Exothermic reactions release heat energy to the surroundings. Endothermic reactions absorb heat energy from the surroundings.

12

13

14

15 Cold and hot packs How do instant hot and cold packs work?

16 Hot pack Pressing the bottom, the diaphragm breaks. Calcium chloride dissolves in water and warms it. The beverage gets warm.

17 Energy Surroundings Exothermic process Heat flows into the surroundings from the system in an exothermic process. Temperature rises Hot pack

18 Hot pack We will repeat the process in a beaker with calcium chloride ( 25 g CaCl 2 ) + 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…….

19 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.

20 Cold pack Energy Surroundings Endothermic process Heat flows into the system from the surroundings in an endothermic process. Temperature falls

21 Cold pack We will repeat the process in a beaker with ammonium nitrate ( 25 g NH 4 NO 3 ) + 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…….

22 Students’ worksheet Fill in the blanks

23 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)

24

25

26 Question What exothermic reactions or endothermic reactions do you know?

27 Liquid Vapor requires energy. This is the reason: a)you cool down after swimming b)you use water to put out a fire. + energy Changes of state

28 Explosions This reaction is exothermic!

29 Photosyntesis This reaction is endothermic!

30 Combustions These reactions are exothermic!

31 Changes in physical state

32 Giving reasons Why does the system give off or take in heat energy?

33 Energy Level Diagrams Endothermic reactions energy time of reaction energy taken in is positive reactants products The products are higher in energy than the reactants

34 The products are higher in energy than the reactants. In this case making the bonds gives you less energy than breaking them.

35 Energy Level Diagrams Exothermic reactions energy Time of reaction reactants products Energy given out is negative The products are lower in energy than the reactants

36 The products are lower in energy than the reactants. In this case making the bonds gives you more energy than breaking them.

37 energy Heat  E <0 Heat given off is negative Ca Cl 2 (s) Ca Cl 2 (aq) Ca Cl 2 (s) Ca Cl 2 (aq)

38 energy Heat  E = kJ/mol Heat given off is negative

39 energy Heat  E>0 Heat absorbed is positive NH 4 NO 3 (s) NH 4 NO 3 (aq) NH 4 NO 3 (s)NH 4 NO 3 (aq)

40 energy Heat  E = + 68 kJ/mol Heat absorbed is positive

41 Exothermic reactions The products have less energy than the reactants. The energy is given out to the surroundings. Ep - Er = E <O The temperature goes up.

42 Endothermic reactions The products have more energy than the reactants. The energy is taken in from surroundings. Ep - Er = E >O The temperature goes down.

43 Direction energy Every energy measurement has three parts: 1. a unit ( Joules of calories); 2. a number how many; 3. a sign to tell direction (negative – exothermic, positive- endothermic).

44 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 Crossword

45

46

47

48

49

50

51

52 Heat pads 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.

53 Head packs

54 Glossary