Topic: Exergonic and endoenergetic reactions - types of reactions

Target group

Elementary school student (grades 7. and 8.)

Core curriculum

Elementary school. Chemistry.

III. Chemical reactions. Student:

4) defines the terms: exothermic reactions and endothermic reactions; gives examples of such reactions.

General aim of education

The student explains what the exo- and endoenergetic reactions consist in and gives examples of such reactions

Key competences

• communication in the mother tongue;

• communication in foreign languages;

• mathematical competence and basic competences in science and technology;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to explain what are exoenergy and endoenergetic reactions;

• to give examples of exoenergetic and endoenergetic reactions taking place in the environment;

• to describe chemical experiments, including: glass and laboratory equipment; chemical reagents, apparatus schema, observations and conclusions;

• to apply safety rules when performing chemical experiments.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• computers with internet access, or tablets;

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers;

• methodician or green, yellow and red cards;

• equipment, laboratory glass and reagents - see description of the experiment in the methodical commentary.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

3. Health and safety – before starting the experiments, students familiarise themselves with the safety data sheets of the substances that will be used during the lesson. The teacher points out the need to be careful when working with them.

Realization

1. The teacher informs students that they will watch the movie „Reaction of aluminum with oxygen” (information in the methodical commentary). Before this happens, they are to formulate a research question and hypotheses and make them in the abstract observation diary, prepared in advance by the teacher or in the notebooks. After the screening, the teacher asks the students what they have observed - after joint observation and conclusions, they are recorded in the indicated place.

2. The lecturer performs the „Decomposition of the substance contained in the baking powder” - information in the methodical commentary - in front of him, he asks the students to formulate a research question and hypotheses and save them in the indicated place. After the show, the students and the teacher set the observations and conclusions and write them down.

3. In relation to the movie „Reaction of aluminum with oxygen” and the „Decomposition of substance contained in baking powder” presentation, the teacher displays the illustrations „Exogenous transformation” and „Endogenous transformation” from the abstract and explains the diagrams. Then he asks the students the question: „What effects accompanied the first reaction, and what other?” - there is a discussion. In its summary students try to define the reaction in terms of energy. The teacher, using the pre‑prepared presentation, explains the concepts of exoenergetic and endoenergetic reactions.

4. The teacher divides the students into groups, distributes sheets of paper and markers, and asks for writing out the similarities and differences between the exoenergetic reaction and the endoenergetic reaction. After the work, the group leaders, using the talking wall technique, discuss the effects of the activities. The teacher sums up this stage of the class.

5. The teacher asks students to give examples of reactions from the human environment, including the division into exo- and endoenergetics - discussion is underway; the teacher also takes part in it, supporting students and completing information.

6. At the end of the lesson, the teacher asks students to do an interactive exercise - individual work.

Summary

1. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

Homework

1. Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

2. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Exergonic and endoenergetic reactions - types of reactions

All chemical reactions are accompanied by energy effects. Sometimes these are effects visible to the naked eye, and sometimes - changes so small that these can go unnoticed. Depending on the direction of energy flow, chemical changes are divided into two groups. The reactions during which energy is released into the environment are called exergonic reactions. On the other hand, reactions accompanied by the absorption of energy from the environment are called endoenergetic reactions. Energy released or absorbed by reacting substances can be in the form of heat, light or work.

Exergonic reactions are not only those that are accompanied by heat and light emission. That are also the reactions during which work is carried out by the emitted gas. When liquids and solids react with each other to form a gas, there may be a thousand‑fold or even a larger increase in the volume of products formed in relation to the volume of substrates. The resulting gas displaces the atmospheric air. If the volume increase occurs in a very short time, an explosion occurs. Air bags in cars uses sodium azide – a substance with the formula ${\mathrm{NaN}}_3$. This chemical compound during the collision, under the influence of an electrical impulse, immediately decomposes. Nitrogen is then formed, which in a fraction of a second fills up the entire airbag and protects the passenger against additional injuries. The reaction of sodium azide analysis occurs according to the equation:

$\text{2}{\text{NaN}}_{\text{3}}\text{→}\text{2N}\text{a}\text{+ 3}{\text{N}}_{\text{2}}$

$\text{sodium azide → sodium + nitrogen}$

• All chemical reactions, in order to start, require a certain amount of energy. Every chemical change needs a different amount of this energy.

• Due to energy effects, we divide chemical reactions into exergonic and endoenergetic.

• Exergonic reactions are chemical changes during which energy from the reaction system is released into the environment in the form of heat, light or work.

• Endoenergetic reactions are chemical changes that take place with energy intake from the environment.

• Combustion reactions always occur with the separation of energy, which is why these are included in exergonic reactions.