What is the interaction between two or more chemicals that produce new chemicals?
The focus ideas of pushes and pulls is explored through Show
Contrasting student and scientific viewsStudent everyday experiencesChildren will have experienced many examples of chemical change without actually realising it. They are familiar with burning, cooking, rusting and chemical processes that appear to involve dissolving. However at this level students don't see new materials being produced as a result of chemical change, rather they see that existing materials have merely been modified in some way. For example they see smoke as part of the wood that is somehow released when the wood burns. Because students rarely understand the concept of ‘a substance’ they don't see substances being changed. Yet an understanding of chemical change is fundamental to appreciating the role of chemistry in their lives and at this level students can begin to appreciate this. Students frequently believe that to get something new, things just need to be mixed together. When a chemical reaction does take place, they believe that one or other of the reactants is simply modified; it hasn't really changed. For example, students consider that rust is still iron/steel; it has just gone brown. Similarly, rust flaking off is usually not noticed – it is thought that the iron just disappears. Gas bubbles that are frequently produced when a tablet dissolves in water are often not seen by students as a new substance. Processes like cordial mixing with water, the use of colouring in food, freezing and boiling are seen as similar to chemical changes like those involved in cooking eggs. Research: Johnson (2002) In combustion, children frequently believe materials like wood or paper just disappear - after all there is not much of the product left to see. In their view, air has little to do with burning. In burning carbon based materials such as wood, students believe that charcoal (carbon) appears from the burning rather than the material. Research: Arizona State University (2001) Because so many reactions children know about are involved in things like cooking and burning, they assume that heat is always necessary for reactions to occur. In everyday language, the word ‘chemical’ is often used as a label for undesirable things that shouldn't be in foods or cosmetics. Hence students may regard chemicals as a group of substances found in laboratories rather than seeing all the substances in foods (for example) as chemicals. Scientific viewAll materials are made of chemicals. Chemical reactions involve interaction between chemicals such that all reactants are changed into new materials. The properties of the new materials are different from those of the reactants. This is distinct from other changes such as evaporation, melting, boiling, freezing and mixing where changes involve no new substances. While heat is often necessary to start reactions, this need not be the case. Chemical reactions involve breaking chemical bonds between reactant molecules (particles) and forming new bonds between atoms in product particles (molecules). The number of atoms before and after the chemical change is the same but the number of molecules will change. Although many chemical reactions proceed quickly, small, slow changes such as rusting or biological processes can take place over much longer periods of time. Chemical reactions are reversible (a fact often omitted in many science texts) but in practice most differ from other changes children observe, such as melting, by being very difficult to reverse. Humans use chemical reactions to produce a wide range of useful materials; the breakdown of waste materials also involves chemical reactions that occur naturally in the environment. For some human made wastes, there are no such reactions and they cause problems as a result. Critical teaching ideasIn teaching about chemical reactions at this level the emphasis should be on improving student understanding of the importance of chemical reactions in our lives in producing many of the things we take for granted as well as improving their recognition and understanding of what is involved in a chemical change. It is not necessary at this stage to talk about particles such as atoms or molecules or chemical bonds.
Explore the relationships between ideas about chemical reactions in the Concept Development Maps – (Atoms & Molecules, Chemical Reactions, Conservation of Matter, States of Matter) In learning about chemical reactions students will need to describe various substances, which at this level will be materials they are familiar with (the kitchen and changes involving cooking are very good starting points). They will need to be able to identify changes in these substances with the purpose of eventually recognising when new chemicals have been produced i.e. a chemical change has taken place. As mentioned above, this is can be difficult as students often fail to see the difference between an egg white going through a change from liquid to solid as it is cooked and changes such as melting chocolate or boiling water which do not involve chemical change. Teaching will need to be focused on what happens when new substances are formed. These ideas are also explored in the focus idea Problems with classifying. Environmental effects of chemical reactions can also be considered, for example how we dispose of some chemicals once they are produced, in forms such as plastic bags. Open up discussion via a shared experienceInitial teaching activities should aim to bring out students’ existing ideas. At this stage it is important that students are encouraged to put up their ideas and discuss them in small groups. All alternatives should be considered with no resolution at this stage. A starting activity could be observing the burning of a candle and discussing the changes that take place. Here the distinction can be made between the melting of the wax and the appearance of new materials. Questions posed could include:
Promote reflection on and clarification of existing ideasActivities which provide problems to be explored and challenge existing ideas are useful in encouraging students to seek new explanations for things they observe. Students should investigate a number of changes and ask questions similar to those above. In all of these students should be encouraged to observe the changes that take place and to identify what products are formed. Discussion can also centre on how these are different from the starting materials. Some examples could include:
Practise using and build the perceived usefulness of a scientific model or ideaOther activities can involve chocolate making. Students can be encouraged to look for the differences between making chocolate where the chocolate melts and the production of caramel/toffee where the sugar changes into something different. There are many other similar chemical changes that can be investigated - further cooking activities can include: making a chocolate cake, melting and browning cheese, making honeycomb, baking bread, poaching eggs and making toast. Other changes can include the setting of two component glues like Araldite and mixing steel wool and a solution of copper sulfate (available from plant nurseries). Oxygen is a very important reactant in many chemical reactions and students can investigate changes involving this component of air. Clarify and consolidate ideas for/by communication to othersIt is important at this stage to clarify and consolidate what students have observed and to focus on what happens in a chemical reaction which is different from melting, boiling and freezing. To achieve this students could be asked in groups to make mini posters which show the changes that take place in the one or more of the reactions they have seen, particularly comparing the products with the starting materials and demonstrating how they are different. This can be assisted by using new names for the products, such as ‘soot’ or ‘carbon dioxide’. Students then present their posters to the class. Resulting class discussion should bring out student ideas, examine alternatives and move to more accepted scientific views about chemical reactions. Activities should be carried out which test the usefulness of the chemical reactions model and further consolidate student ideas about what constitutes a chemical reaction. Students can be further encouraged to compare the products with the starting materials. For example students could investigate the rusting of a steel nail under different conditions (such as in air/water/salty water). To further develop students' appreciation of the role of chemical change in their lives, they could research the production of metals from ores (such as aluminium and steel) or the production of plastics and synthetic fibres. The emphasis in this exploration is on the importance of chemical change in producing the materials we use every day. Further resourcesScience related interactive learning objects can be found on the FUSE Teacher Resources page. To access the interactive learning object below, teachers must login to FUSE and search by Learning Resource ID:
What is it called when 2 or more chemicals react?A combination reaction is a reaction in which two or more substances combine to form a single new substance. Combination reactions can also be called synthesis reactions. The general form of a combination reaction is: A+B→AB. One combination reaction is two elements combining to form a compound.
What is it called when you combine two chemicals?A chemical reaction occurs when two or more substances are combined to form a new substance and cannot be separated back into its original substances.
What helps an interaction between two chemicals to occur?Chemical Reactions
For a chemical reaction to occur, when two or more molecules collide, they must collide with the necessary force and orientation to cause the bonds between atoms to break in order for new molecules to be formed.
What is it called when two chemicals interfere with each other's action?In toxicology, synergism refers to the effect caused when exposure to two or more chemicals at one time results in health effects that are greater than the sum of the effects of the individual chemicals.
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