Chemical Reactions and Equations: CBSE Science

• Science encompasses the systematic study of the natural and physical world through observation and experimentation.
• CBSE refers to the Central Board of Secondary Education, a national level board of education in India for public and private schools.

Chemical Reactions and Equations

• A chemical reaction involves the rearrangement of atoms and molecules to form new substances.
• Chemical equations represent chemical reactions using symbols and formulas of the substances involved.
• Balanced chemical equations have the same number of atoms of each element on both the reactant and product sides, obeying the law of conservation of mass.
• Types of chemical reactions include combination, decomposition, displacement, double displacement, and redox reactions.
• Combination reactions involve the joining of two or more reactants to form a single product.
• Decomposition reactions involve the breakdown of a single reactant into two or more products.
• Displacement reactions involve the replacement of one element by another in a compound.
• Double displacement reactions involve the exchange of ions between two compounds, forming new compounds.
• Redox reactions involve the transfer of electrons between reactants; oxidation is the loss of electrons, and reduction is the gain of electrons.
• Corrosion is the deterioration of a metal due to its reaction with the environment.
• Rancidity is the oxidation of fats and oils in food, resulting in unpleasant taste and odor.
• Antioxidants can be added to food to prevent rancidity.

Acids, Bases, and Salts

• Acids are substances that release hydrogen ions (H+) when dissolved in water and turn blue litmus red.
• Bases are substances that release hydroxide ions (OH-) when dissolved in water and turn red litmus blue.
• Salts are formed by the reaction of an acid and a base.
• pH is a measure of the acidity or basicity of a solution, with values ranging from 0 to 14.
• A pH of 7 is neutral, pH less than 7 is acidic, and pH greater than 7 is basic.
• Strong acids and bases completely ionize in water, while weak acids and bases partially ionize.
• Neutralization is the reaction between an acid and a base to form a salt and water.
• Indicators are substances that change color in the presence of acids or bases.
• Common indicators include litmus, methyl orange, and phenolphthalein.
• Some important salts include sodium chloride (NaCl), sodium hydroxide (NaOH), bleaching powder (CaOCl2), baking soda (NaHCO3), washing soda (Na2CO3.10H2O), and plaster of Paris (CaSO4.1/2 H2O).
• Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.

Metals and Non-metals

• Metals are generally hard, lustrous, malleable, ductile, and good conductors of heat and electricity.
• Non-metals are generally soft, dull, brittle, and poor conductors of heat and electricity.
• Metals react with oxygen to form metallic oxides, which are basic in nature.
• Non-metals react with oxygen to form non-metallic oxides, which are acidic in nature.
• Metals react with water to form metal hydroxides and hydrogen gas.
• Reactivity series is the arrangement of metals in the decreasing order of their reactivity.
• Ionic compounds are formed by the transfer of electrons between metals and non-metals.
• Covalent compounds are formed by the sharing of electrons between non-metals.
• Metallurgy is the process of extracting metals from their ores.
• Corrosion of metals can be prevented by coating them with paint, oil, grease, or by galvanization (coating with zinc).

Carbon and Its Compounds

• Carbon is a versatile element that can form a large number of compounds due to its tetravalency and catenation property.
• Catenation is the ability of carbon atoms to form long chains and rings.
• Carbon forms covalent bonds with other elements.
• Hydrocarbons are compounds containing carbon and hydrogen only.
• Saturated hydrocarbons contain single bonds between carbon atoms (alkanes), while unsaturated hydrocarbons contain double or triple bonds (alkenes and alkynes).
• Functional groups are atoms or groups of atoms that determine the chemical properties of organic compounds (e.g., alcohols, aldehydes, ketones, carboxylic acids).
• Homologous series is a series of organic compounds with the same functional group and similar chemical properties, differing by a CH2 group.
• Isomers are compounds with the same molecular formula but different structural formulas.
• Ethanol (C2H5OH) and ethanoic acid (CH3COOH) are important carbon compounds with various uses.
• Soaps and detergents are used for cleaning and emulsifying grease and dirt.

Periodic Classification of Elements

• Elements are classified based on their properties.
• Döbereiner's triads grouped elements with similar properties in sets of three.
• Newlands' law of octaves arranged elements in order of increasing atomic mass, with every eighth element having similar properties.
• Mendeleev's periodic table arranged elements in order of increasing atomic mass and grouped elements with similar properties together.
• Mendeleev left gaps for undiscovered elements and predicted their properties.
• The modern periodic table is based on increasing atomic number.
• Groups (vertical columns) contain elements with similar valence electron configurations and chemical properties.
• Periods (horizontal rows) represent elements with the same number of electron shells.
• Metals are located on the left side of the periodic table, non-metals on the right side, and metalloids (semi-metals) in between.
• Atomic size, metallic character, and non-metallic character vary periodically across periods and down groups.

Life Processes

• Life processes are the basic functions performed by living organisms to maintain life (e.g., nutrition, respiration, transportation, excretion).
• Nutrition is the process of obtaining nutrients from food.
• Autotrophic nutrition: organisms make their own food (e.g., plants through photosynthesis).
• Heterotrophic nutrition: organisms obtain food from other organisms (e.g., animals).
• Respiration is the process of breaking down food to release energy.
• Aerobic respiration uses oxygen, while anaerobic respiration does not.
• Transportation involves the movement of substances within the body (e.g., blood circulation in animals, transport of water and minerals in plants).
• Excretion is the removal of waste products from the body (e.g., urination in animals, removal of excess water in plants).

Control and Coordination

• Control and coordination are the processes that regulate and integrate various bodily functions.
• Nervous system: uses electrical and chemical signals to transmit information (neurons, brain, spinal cord).
• Endocrine system: uses hormones to transmit information (glands, hormones).
• Plant hormones (phytohormones) regulate plant growth and development (e.g., auxins, gibberellins, cytokinins, abscisic acid).
• Movement in plants can be tropic (directional) or nastic (non-directional).
• Reflex actions are rapid, automatic responses to stimuli controlled by the spinal cord.

How do Organisms Reproduce?

• Reproduction is the process by which organisms produce new individuals of the same kind.
• Asexual reproduction involves a single parent (e.g., fission, fragmentation, regeneration, budding, vegetative propagation).
• Sexual reproduction involves two parents and the fusion of gametes (sex cells).
• Sexual reproduction in flowering plants involves pollination (transfer of pollen) and fertilization (fusion of male and female gametes).
• Human reproductive system: male (testes, sperm) and female (ovaries, eggs) reproductive organs.
• Fertilization in humans occurs internally.
• Reproductive health and methods of contraception are important for family planning and preventing sexually transmitted diseases.

Heredity and Evolution

• Heredity is the transmission of traits from parents to offspring.
• Genetics is the study of heredity and variation.
• Gregor Mendel's experiments with pea plants revealed the laws of inheritance.
• Genes are the units of heredity located on chromosomes.
• DNA (deoxyribonucleic acid) is the genetic material that carries hereditary information.
• Evolution is the gradual change in the characteristics of a species over time.
• Evidence for evolution includes fossils, comparative anatomy, embryology, and molecular biology.
• Natural selection is the mechanism of evolution, where organisms with advantageous traits are more likely to survive and reproduce.
• Speciation is the process by which new species arise.

Light – Reflection and Refraction

• Light is a form of energy that enables us to see objects.
• Reflection is the bouncing back of light from a surface.
• Laws of reflection: angle of incidence equals angle of reflection; incident ray, reflected ray, and normal lie in the same plane.
• Mirrors are polished surfaces that reflect light (e.g., plane mirrors, concave mirrors, convex mirrors).
• Spherical mirrors have a curved reflecting surface.
• Concave mirrors converge light rays, while convex mirrors diverge light rays.
• Refraction is the bending of light as it passes from one medium to another.
• Laws of refraction: Snell's law (ratio of sines of angles of incidence and refraction is constant); incident ray, refracted ray, and normal lie in the same plane.
• Lenses are transparent materials that refract light (e.g., convex lenses, concave lenses).
• Convex lenses converge light rays, while concave lenses diverge light rays.
• Power of a lens is the reciprocal of its focal length, measured in diopters (D).

The Human Eye and the Colourful World

• The human eye is a complex organ that enables us to see.
• Parts of the eye: cornea, iris, pupil, lens, retina, optic nerve.
• Accommodation is the ability of the eye to focus on objects at different distances.
• Defects of vision include myopia (nearsightedness), hyperopia (farsightedness), presbyopia (old age sight), and astigmatism.
• Myopia is corrected using concave lenses, hyperopia is corrected using convex lenses.
• Refraction of light through a prism causes dispersion, splitting white light into its constituent colors (VIBGYOR).
• Atmospheric refraction causes twinkling of stars and apparent flattening of the sun at sunrise and sunset.
• Scattering of light by atmospheric particles causes the sky to appear blue and the sun to appear reddish at sunrise and sunset.

Electricity

• Electric charge is a fundamental property of matter.
• Electric current is the rate of flow of electric charge through a conductor, measured in amperes (A).
• Electric potential difference is the work done to move a unit charge from one point to another, measured in volts (V).
• Ohm's law relates voltage, current, and resistance (V = IR).
• Resistance is the opposition to the flow of electric current, measured in ohms (Ω).
• Factors affecting resistance: length, area of cross-section, material, and temperature.
• Series combination of resistors: total resistance is the sum of individual resistances.
• Parallel combination of resistors: reciprocal of total resistance is the sum of reciprocals of individual resistances.
• Electric power is the rate at which electric energy is consumed or dissipated, measured in watts (W).
• Electric energy is the total amount of energy consumed by an electrical appliance, measured in kilowatt-hours (kWh).

Magnetic Effects of Electric Current

• A magnetic field is a region around a magnet or a current-carrying conductor where magnetic force is experienced.
• Magnetic field lines represent the direction and strength of the magnetic field.
• A current-carrying conductor produces a magnetic field around it.
• The direction of the magnetic field can be determined using the right-hand thumb rule.
• A current-carrying conductor placed in a magnetic field experiences a force.
• The direction of the force can be determined using Fleming's left-hand rule.
• Electric motor converts electrical energy into mechanical energy.
• Electromagnetic induction is the phenomenon of inducing an electric current in a conductor by changing the magnetic field around it.
• Electric generator converts mechanical energy into electrical energy.
• Domestic electric circuits use alternating current (AC).

Sources of Energy

• Sources of energy are classified as renewable (inexhaustible) and non-renewable (exhaustible).
• Fossil fuels (coal, petroleum, natural gas) are non-renewable sources of energy.
• Renewable sources of energy include solar energy, wind energy, hydro energy, geothermal energy, and biomass.
• Solar energy can be harnessed using solar cells and solar panels.
• Wind energy can be harnessed using windmills and wind turbines.
• Hydro energy is obtained from the kinetic energy of flowing water.
• Geothermal energy is obtained from the heat inside the Earth.
• Biomass is organic matter that can be used as a fuel.
• Nuclear energy is obtained from nuclear reactions.

Our Environment

• Environment includes all the biotic (living) and abiotic (non-living) factors surrounding us.
• Ecosystem is a community of living organisms interacting with each other and their physical environment.
• Food chains and food webs show the flow of energy and nutrients in an ecosystem.
• Trophic levels represent the position of an organism in a food chain.
• Environmental problems include pollution, deforestation, and ozone depletion.
• Pollution is the contamination of the environment with harmful substances.
• Deforestation is the clearing of forests.
• Ozone depletion is the thinning of the ozone layer, which protects us from harmful UV radiation.
• Waste management involves reducing, reusing, and recycling waste materials.

Management of Natural Resources

• Natural resources are materials or substances occurring in nature that can be used for economic gain.
• Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
• Conservation of natural resources is essential for sustainable development.
• Forests and wildlife can be conserved by protecting habitats, preventing poaching, and promoting afforestation.
• Water resources can be managed by building dams, conserving rainwater, and preventing water pollution.
• Coal and petroleum can be conserved by using them efficiently and developing alternative sources of energy.

Explore chemical reactions and equations with symbols and formulas. Understand combination, decomposition, displacement, and redox reactions. Master balancing equations to obey the law of conservation of mass.