Topic: Exergonic and endoenergetic reactions – oxidation and combustion

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 oxidation and combustion process is about

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:

• what effects may accompany chemical reactions;

• which distinguishes combustion from other redox reactions;

• exchange examples of oxidation, including combustion, from everyday life and the human environment.

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;

• interactive whiteboard, tablets/computers;

• methodician or green, yellow and red cards;

• sheets of paper, markers, glutaki.

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 divides the students into groups, gives out job cards and refers them to the textbook, abstract and the internet asking them to answer the question „What effects can accompany chemical reactions?”. Students write information useful in the work cards to answer. After completing the work, the groups present their observations. The teacher summarizes the activities of the students and possibly completes the messages.

2. The teacher informs students that they will watch the film „Burning magnesium in 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.

3. In relation to the film „Burning magnesium in oxygen”, the teacher asks the students the question: „What effects did burning accompany?”, Initiating the discussion. He asks for a combustion reaction to be defined, then displays on the multimedia presentation an explanation of the concept of „combustion”.

4. The lecturer presents images in a multimedia presentation, for example with the phenomenon of rust, or shows various props. The students have already learned the rusting process - in order to remind them, the teacher asks questions, eg what conditions have to be met, that this process will happen, what accompanies it, how this process is called, how it can be defined - the discussion is going on. In its summary, the teacher displays the explanation of the term „oxidation”.

5. The teacher divides the students into groups, distributes sheets of paper and markers. It asks to be listed, which distinguishes the combustion reaction from other oxidation reactions. After the end of work, group leaders using the technique of a talking wall discuss the effects of actions. The teacher sums up this stage of the class.

6. The teacher gives various examples of chemical reactions (combustion and oxidation) and asks people to write chemical equations of these reactions using symbols and formulas of chemical compounds, including balancing equations, eg iron rusting, magnesium combustion, sulfur combustion, oxidation of sulfur dioxide to sulfur trioxide, oxidation of sodium, combustion of hydrogen in oxygen. The rest make entries in the notebooks.

7. At the end of the lesson, the teacher asks students to do interactive exercises - 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 – oxidation and combustion

All chemical reactions are accompanied by an energy effect. Under this concept, we mean the emission of energy into the environment or its uptake by reacting substances. During the conversion of substrates into products, the system may give energy in various forms to the environment – in the form of heat, light, work or even electricity. The same type of energy during other chemical changes can be absorbed by reacting substrates. Whether energy will be released during the reaction or whether energy is consumed depends on the substances reacting with each other.

It may be surprising that regardless of whether substances react with one another or emit energy, each chemical conversion requires a certain amount of energy, without which it cannot be initiated. Before using the heat released during the reaction of carbon with oxygen (coal burning), you need to provide the substrate with the right amount of energy. After initiation, the reaction (combustion) proceeds spontaneously. This is also the case when motor vehicles move. Neither petrol nor diesel fuel is immediately ignited in the presence of oxygen from the air. What is needed is an additional factor (energy) that would initiate this reaction. In gasoline engines it is an electric spark, while in diesel engines – compression (volume reduction) and fuel heating. These impulses initiate the reaction of fuel with oxygen, which occurs with the release of energy.

All reactions differ in the amount of energy required to initiate them. There are changes that only a small amount of energy is needed to initiate, such as a slight shock, as in the case of substances contained in explosives. Some, however, need more energy to initiate the conversion of substrates into products.

During oxidation, the atom passes from a lower level of oxidation to a higher one (which is equivalent to electron donation). In practice, a given reaction is called oxidation when the increase in the oxidation state concerns a compound or chemical element being the main subject of the reaction. This name is contractual since each oxidation reaction must be accompanied by a reduction reaction. In total, this process is called the redox reaction. As a electron acceptor, a chemical compound (oxidizer) or a positive electrode (anode) may be used. The process of combining substances with oxygen can occur slowly. An example of such a process is the oxidation of iron to iron(III) oxide, which is the main component of rust: steel or iron parts of various objects rust gradually, with no visible energy effects.

 Combining the substance with oxygen can also take place very quickly, with the release of energy in the form of a large amount of heat and light. In this case, combustion occurs. The Combustion reaction is a reaction with oxygen, that proceeds relatively quickly, in a rapid manner; it is accompanied by thermal, light and sometimes even sound effects. Combustion takes place when the entire mass of the combusted substance is oxidized. It occurs when not only there is no smoke or inflammable substances in the ash, but also some of the fuel in the form of steam does not escape.

Conclusion: combustion is also oxidation, while not every oxidation is combustion.

• 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.