>> Physical and chemical phenomena (chemical reactions). Let's experiment at home. External effects in chemical reactions
Physical and chemical phenomena (chemical reactions)
The material in this paragraph will help you figure out:
>what is the difference between physical and chemical phenomena.(chemical reactions);
> what external effects accompany chemical reactions.
In natural history lessons, you learned that various physical and chemical phenomena occur in nature.
Physical phenomena.
Each of you has repeatedly observed how ice melts, water boils or freezes. Ice, water and water vapor consist of the same molecules, so they are one substance (in different states of aggregation).
Phenomena in which a substance does not transform into another are called physical.
Physical phenomena include not only changes in substances, but also the glow of hot bodies, the passage of electric current in metals, the spread of the smell of substances in the air, the dissolution of fat in gasoline, and the attraction of iron to a magnet. Such phenomena are studied by the science of physics.
Chemical phenomena (chemical reactions).
One of the chemical phenomena is combustion. Let's consider the process of burning alcohol (Fig. 46). It occurs with the participation of oxygen contained in the air. When burned, alcohol seemingly turns into a gaseous state, just as water turns into steam when heated. But that's not true. If the gas obtained as a result of the combustion of alcohol is cooled, then part of it will condense into liquid, but not into alcohol, but into water. The rest of the gas will remain. With the help of additional experiment it can be proven that this residue is carbon dioxide.
Rice. 46. Burning alcohol
So the alcohol that burns and oxygen, which participates in the combustion process, are converted into water and carbon dioxide.
Phenomena in which some substances are transformed into others are called chemical phenomena or chemical reactions.
Substances that enter into a chemical reaction are called starting substances, or reagents, and those that are formed are called final substances, or reaction products.
The essence of the chemical reaction considered is conveyed by the following entry:
alcohol + oxygen -> water + carbon dioxide
starting materials final substances
(reagents) (reaction products)
The reactants and products of this reaction are made up of molecules. During combustion, a high temperature is created. Under these conditions, the molecules of the reagents disintegrate into atoms, which, when combined, form molecules of new substances - products. Therefore, all atoms are conserved during the reaction.
If the reactants are two ionic substances, then they exchange their ions. Other variants of interaction of substances are also known.
External effects accompanying chemical reactions.
By observing chemical reactions, you can record the following effects:
Change in color (Fig. 47, a);
gas release (Fig. 47, b);
formation or disappearance of sediment (Fig. 47, c);
appearance, disappearance or change in odor;
release or absorption of heat;
the appearance of a flame (Fig. 46), sometimes a glow.
Rice. 47. Some external effects during chemical reactions: a - appearance
coloring; b - gas release; c - appearance of sediment
Laboratory experiment No. 3
The appearance of color as a result of the reaction
Are solutions of soda ash and phenolphthalein colored?
Add 2 drops of phenolphthalein solution to a portion of soda solution I-2. What color appeared?
Laboratory experiment No. 4
Release of gas as a result of the reaction
Add a little chloride acid to the soda ash solution. What are you observing?
Laboratory experiment No. 5
The appearance of a precipitate as a result of the reaction
Add 1 ml of copper sulfate solution to the soda ash solution. What's happening?
The appearance of a flame is a sign of a chemical reaction, i.e. it indicates a chemical phenomenon. Other external effects can also be observed during physical events. Let's give a few examples.
Example 1. Silver powder obtained in a test tube as a result of a chemical reaction is gray in color. If you melt it and then cool the melt, you will get a piece of metal, but not gray, but white, with a characteristic shine.
Example 2. If you heat natural water, gas bubbles will begin to emerge from it long before boiling. This is dissolved air; its solubility in water decreases when heated.
Example 3. An unpleasant odor in the refrigerator disappears if granules of silica gel, one of the silicon compounds, are placed in it. Silica gel absorbs molecules of various substances without destroying them. Activated carbon works in a similar way in a gas mask.
Example 4 . When water turns into steam, heat is absorbed, and when water freezes, heat is released.
To determine what kind of transformation has occurred - physical or chemical, you should carefully observe it, as well as comprehensively examine the substances before and after the experiment.
Chemical reactions in nature, everyday life and their significance.
Chemical reactions occur constantly in nature. Substances dissolved in rivers, seas, and oceans interact with each other, some react with oxygen. Plants absorb carbon dioxide from the atmosphere, water and dissolved substances from the soil and process them into proteins, fats, glucose, starch, vitamins, other compounds, as well as oxygen.
This is interesting
As a result of photosynthesis, about 300 billion tons of carbon dioxide are absorbed from the atmosphere each year, 200 billion tons of oxygen are released, and 150 billion tons of organic substances are formed.
Reactions involving oxygen, which enters living organisms during respiration, are very important.
Many chemical reactions accompany us in everyday life. They occur during frying meat, vegetables, baking bread, souring milk, fermenting grape juice, bleaching fabrics, burning various types of fuel, hardening cement and alabaster, blackening silver jewelry over time, etc.
Chemical reactions form the basis of such technological processes as the extraction of metals from ores, the production of fertilizers, plastics, synthetic fibers, medicines, and other important substances. By burning fuel, people provide themselves with heat and electricity. Using chemical reactions, they neutralize toxic substances and process industrial and household waste.
The occurrence of some reactions leads to negative consequences. Rusting of iron shortens the life of various mechanisms, equipment, vehicles, and leads to large losses of this metal. Fires destroy housing, industrial and cultural facilities, and historical values. Most foods spoil due to their interaction with oxygen in the air; in this case, substances are formed that have an unpleasant odor, taste and are harmful to humans.
conclusions
Physical phenomena are the phenomena in which each substance is conserved.
Chemical phenomena, or chemical reactions, are the transformation of one substance into another. They can be accompanied by various external effects.
Many chemical reactions occur in the environment, in plants, animals and humans, and accompany us in everyday life.
?
100. Match:
1) dynamite explosion; a) physical phenomenon;
2) solidification of molten paraffin; b) chemical phenomenon.
3) food burning in a frying pan;
4) the formation of salt during the evaporation of sea water;
5) separation of a strongly shaken mixture of water and vegetable oil;
6) fading of dyed fabric in the sun;
7) passage of electric current in the metal;
101. What external effects are accompanied by such chemical transformations: a) burning of a match; b) rust formation; c) fermentation of grape juice.
102. Why do you think some food products (sugar, starch, vinegar, salt) can be stored indefinitely, while others (cheese, butter, milk) quickly spoil?
Experimenting at home
External effects in chemical reactions
1. Prepare small amounts of aqueous solutions of citric acid and baking soda. Pour portions of both solutions together into a separate glass. What's happening?
Add a few soda crystals to the remainder of the citric acid solution, and a few citric acid crystals to the remainder of the soda solution. What effects do you observe - the same or different?
2. Pour some water into three small glasses and add 1-2 drops of brilliant green alcohol solution, known as “zelenka,” to each. Add a few drops of ammonia to the first glass, and citric acid solution to the second. Has the color of the dye (green) in these glasses changed? If so, how exactly?
Write down the results of the experiments in a notebook and draw conclusions.
Popel P. P., Kryklya L. S., Chemistry: Pidruch. for 7th grade zagalnosvit. navch. closing - K.: VC "Academy", 2008. - 136 p.: ill.
Lesson content lesson notes and supporting frame lesson presentation interactive technologies accelerator teaching methods Practice tests, testing online tasks and exercises homework workshops and trainings questions for class discussions Illustrations video and audio materials photographs, pictures, graphs, tables, diagrams, comics, parables, sayings, crosswords, anecdotes, jokes, quotes Add-ons abstracts cheat sheets tips for the curious articles (MAN) literature basic and additional dictionary of terms Improving textbooks and lessons correcting errors in the textbook, replacing outdated knowledge with new ones Only for teachers calendar plans training programs methodological recommendationsCHEMICAL AND PHYSICAL PHENOMENA The purpose of the lesson:
melting
crystallization
condensation
evaporation
Physical phenomena in chemistry
Filtration
Distillation
Evaporation
Physical and chemical phenomena
LIGHTNING
Physical and chemical phenomena
Physical and chemical phenomena
Eruption
Physical and chemical phenomena
Physical and chemical phenomena
Leaves in autumn
Physical and chemical phenomena
Fire in the forest
Physical and chemical phenomena
Machine corrosion
Physical and chemical phenomena
Ice melting
Physical and chemical phenomena
Leaf rotting
Physical and chemical phenomena
Sauerkraut
I V L E N I
F I Z I C H E S K I E
H I M I C H E S K I E
Signs of a chemical reactionRelease or absorption of heat
Change
Precipitation (dissolution)
Selection
Selection
Conditions for the occurrence and occurrence of chemical reactions
catalyst
Heating
Ultraviolet
irradiation
Experiment 1. Floating paraffin.
They placed a piece of paraffin in a porcelain cup and heated it. After the paraffin melted, the flame was extinguished. When the cup cooled down, we examined the paraffin.
Write down your observations (fill in the blanks in the sentences). What is this phenomenon?
Observations. When paraffin is heated, it ________ goes into the ____________ state.
Conclusion: This is a _____________ phenomenon.
Experiment 2. Evaporation of water.
Pour some water into the test tube and heat it.
Observations: When heated, water boils, and its _________________
Conclusion: This is a _________________ phenomenon.
Based on experiments, tell me what phenomenon is called physical?
PHYSICAL are those phenomena in which these substances do not transform into others, but a change in the aggregate state of the substance or its form occurs.
Experiment 3. “Dissolving soda.”
Add acid (acetic vinegar) to the white crystalline substance (soda). Record your observations. What is this phenomenon?
Observations. In this case, there is a rapid release of _______. The ghost of transformation is the release of _______.
Conclusion. This is a ____________________ phenomenon.
Experiment 4. “Interaction of solutions.”
Pour a blue salt solution (CuCl₂) and a colorless solution – NaOH into a test tube. Record your observations.
What is this phenomenon?
A sign of transformation is the loss of ____ and _____ colors.
Conclusion. This is a __________________ phenomenon.
Find a match. Option 1: Option 2:
Physical phenomenon
chemical phenomenon
2. Which of the phenomena are chemical?
1) water freezing
2) combustion of sulfur
3) decomposition of mercury oxide when heated
4) melting metals
5) candle burning
6) air liquefaction
7) natural gas combustion
1. Which of the phenomena are considered physical?
a) boiling water
b) decomposition of water by electric current
c) interaction of zinc with hydrochloric acid
d) melting metal
d) melting snow
f) decomposition of carbonic acid into carbon dioxide and water
g) freezing of water.
CHEMICAL AND PHYSICAL PHENOMENA
Physical: Chemical:
a– d – e – g 2 – 3 – 5 – 7
Homework level I: - Read §25 and §26,
Bibliography:
Explanatory note
Introduction (7 hours)
Bodies and substances (19 h)
Temperature. Thermometers.
Divisibility of substances. Structure of atom and ion.
Solutions and suspensions.
Class
Physical and chemical phenomena (8 hours)
Chemical reactions as processes of formation of some substances from others. Signs of chemical phenomena and conditions for their occurrence.
Explanation of chemical reactions from a molecular point of view. The breakdown of substances and molecules into atoms or ions, the formation of new substances from them. Conservation of mass of substances in chemical reactions.
Repetition of signs of chemical elements. Compound and decomposition reactions. Drawing up equations for compounding and decomposition reactions.
Substances in nature. The concept of classes of inorganic and organic substances (15 h)
Oxides are complex substances consisting of two chemical elements, one of which is oxygen. Examples of the most common oxides, their distribution in nature and use.
Acids. Basic information about acids, examples of the most common acids. Use of acids in the household and everyday life. Rules for handling acids. Recognition of acids.
Grounds. General information about bases, soluble bases – alkalis; lime water, slaked lime. Application of principles in the national economy and everyday life. Rules for handling grounds. Recognition of bases. Neutralization reaction.
The concept of indicators. Action of acids and bases on indicators.
Salts are complex substances that contain metal ions and acidic residues. Examples of salts, their distribution in nature. Properties and uses of a number of salts: table salt, soda, copper sulfate, etc.
Organic and inorganic substances. Proteins, fats and carbohydrates are the most important nutrients for the human body. Recognition of certain proteins, fats, carbohydrates.
Natural gas and oil. The origin of natural gas, oil, coal as products of decay of various organic residues without air access at high pressures. The most important oil and gas fields in Russia, their importance as sources of various types of fuel and as the most important raw material for the chemical industry.
Man and nature (11 h)
Energy sources. Various types of energy sources: solar energy, mineral fuel, nuclear fuel. Flammable energy sources. Digestion as a process of human energy replenishment. The importance of solar energy for life on Earth.
Outstanding natural scientists, their role in creating the foundations of natural science. The main directions of modern scientific research in the field of physics and chemistry.
The need to create artificial materials. Examples of artificial materials and their use: ceramics, ferrites, super-strong alloys, artificial diamonds, liquid crystals, etc. Information on methods of growing artificial crystals. Instructions for conducting a home experiment on growing a crystal.
Polymers. Polyethylene, polyvinyl chloride, polystyrene and other plastics. Natural and chemical fibers. Use of these materials in everyday life.
Rubber and rubber. Recognition of natural and chemical fibers. Rubber, its properties and production. Vulcanization of rubber, rubber and ebonite.
Environmental pollution. The main factors of the harmful effects of human activity on the environment. Environmental disasters, military actions. Harmful production emissions. The need to monitor the state of the atmosphere and the main methods of its implementation. The need to combat environmental pollution.
The need to save natural resources and use new technology. Discussion of the environmental condition at the school and in the area adjacent to it. Drawing up a plan for specific tasks to improve the environmental situation, which can be completed during summer school practice.
Modern science and production. Means of communication. Knowledge, its role in human life and society. How people understand the world around them (science yesterday, today, tomorrow).
Production management: the role of automation, electronics. Computerization of production. Robots.
Communications and information transmission: telephone, radio, television.
QUESTIONS ABOUT PHYSICS
1. What does physics study? Physical body, physical phenomenon, physical quantity, substance.
2. Measurements. Measuring instruments.
3. Aggregate states of matter.
4. Movement and interaction of particles of matter.
5. Mass of the substance. Density.
6. Interaction of bodies. Force.
7. Body pressure on the support.
8. Pressure in liquids and gases.
9. Mechanical movement. Speed
10. Thermal expansion. Heat transfer
11. Electrification of bodies.
12. Electric current. Current sources.
13. Light sources. Reflection and refraction of light.
14. Simple mechanisms
15. Permanent magnets. Magnetic interaction
Sample practical tasks
Draw a table in your notebook and distribute the following words in it: lead, thunder, rails, blizzard, aluminum, dawn, blizzard, Moon, alcohol, scissors, mercury, snowfall, table, copper, helicopter, oil, boiling, blizzard, shot, flood .
Carefully pour a full teaspoon of granulated sugar into a glass filled to the brim with tea, so that the tea does not overflow over the edge of the glass. Why?
Why do we pass by the dining room and know what dish they prepare there?
Which shoes make your feet feel colder: loose or tight ones? What role can a wool sock play?
Why are the handles of pliers always longer than the cutting part?
Explanatory note
The proposed program is implemented in the textbook “Introduction to Natural Science Subjects. Natural science. 5-6 grades”, authors A.E. Gurevich, D.A. Isaev, L.S. Pontak.
The program is compiled on the basis of the fundamental core of the content of general education and the requirements for the results of mastering the basic educational program of basic general education, presented in the Standard of Basic General Education.
Introduction (7 hours)
Nature is living and inanimate. Natural phenomena. Man is part of nature. Man influences nature. The need to study nature and respect it. Protection of Nature.
Chemistry is the science of nature. Bodies and substances. What does chemistry study? Scientific methods of studying nature: observation, experience, theory.
Introduction to the simplest chemical equipment: test tube, flask, beaker, funnel, pipette, spatula, plastic and metal stands, test tube holder. Heating device, features of the flame. Rules for heating a substance.
Measuring instruments: scales, thermometer, beaker (units of measurement, instrument scale, division value, measurement limit, rules of use).
Bodies and substances (19 h)
Characteristics of bodies and substances (shape, volume, color, smell). Solid, liquid and gaseous states of matter.
Temperature. Thermometers.
Divisibility of substances. Molecules, atoms, ions. An idea of the particle size of a substance. Movement of particles of matter. Relationship between particle speed and temperature. Diffusion in solids, liquids and gases. Interaction of particles of matter and atoms. Explanation of the structure of solids, liquids and gases from a molecular point of view. Structure of atom and ion.
Chemical elements (oxygen, nitrogen, hydrogen, iron, aluminum, copper, phosphorus, sulfur). Signs of chemical elements. Periodic system D.I. Mendeleev.
Simple and complex substances (oxygen, nitrogen, water, carbon dioxide, table salt).
Oxygen. Combustion in oxygen. Photosynthesis. Air is a mixture of gases.
Solutions and suspensions.
Water. Water as a solvent. Purification of natural water.
Physical and chemical phenomena (8 hours)
Melting and solidification. Melting snow, freezing water, smelting iron and steel, making casting parts.
Evaporation of liquids. Condensation.
