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Why is the ripening of a tomato considered a chemical change?The ripening of a tomato is a chemical change because its internal chemical composition changes, a new substance is formed, and it results in an irreversible color shift from green to red.Give two examples of natural changes.Two examples of natural changes are the changing of seasons and the melting of glaciers.What are human-made changes?Human-made changes are those changes that occur specifically due to human efforts or activities, such as weaving cloth or cooking food.Why is the rusting of iron classified as a slow change?Rusting of iron is classified as a slow change because it requires a long duration of many days, months, or years to complete.Provide two examples of fast changes.Two examples of fast changes are the bursting of crackers and the burning of a matchstick.Why is rainfall sometimes considered both a desirable and an undesirable change?Rainfall is desirable for farmers during the sowing of seeds but becomes undesirable when it occurs during the harvesting of crops.What is a periodic change?A periodic change is a change that recurs regularly at fixed intervals of time, such as the swinging of a clock’s pendulum.What are non-periodic changes?Non-periodic changes are changes that do not occur at fixed intervals of time, such as coughing or volcanic eruptions.Why is the curdling of milk an irreversible change?Curdling of milk is irreversible because milk cannot be recovered from curd by reversing any of the conditions.Define a physical change.A physical change is a change in which only the physical properties of a substance change without forming any new substance or altering its chemical composition.What are physical properties of a substance?The physical properties of a substance include its shape, size, color, and state of matter.State the process of condensation.Condensation is the process in which a gas changes directly into its liquid state at a fixed temperature upon cooling.How does evaporation differ from boiling in terms of where it takes place?Evaporation takes place only from the surface of the liquid, whereas boiling takes place throughout the entire bulk of the liquid.Why do water droplets appear on the outer surface of a glass containing ice cubes?Water droplets appear because the water vapour present in the surrounding air condenses upon touching the cold outer surface of the glass.How can salt be recovered from a salt solution?Salt can be recovered from a salt solution by completely evaporating the water over heat, which leaves a white residue of salt behind in the dish.Name three substances that undergo sublimation.Three substances that undergo sublimation are camphor, ammonium chloride, and solid carbon dioxide.Why is magnetising a piece of iron considered a physical change?Magnetising iron is a physical change because no new substance is formed, and the iron retains its original chemical properties.Define a chemical change.A chemical change is a change in which the chemical composition and properties of a substance are altered, resulting in the formation of one or more new substances.Write the chemical equation for respiration in living organisms.The chemical equation for respiration is Glucose + Oxygen → Carbon dioxide + Water + Energy.What is observed when a lighted matchstick is brought near the mouth of a test tube releasing hydrogen gas?A pop sound is heard when a lighted matchstick is brought near the test tube, confirming the presence of hydrogen gas.How can we demonstrate that mixing iron filings and sulphur powder is a physical change?Mixing them is a physical change because the iron filings can be easily separated from the sulphur powder using a magnet.What happens to the magnetic properties of iron when it is heated strongly with sulphur?When heated strongly with sulphur, iron reacts to form iron sulphide and entirely loses its magnetic property, so it is no longer attracted to a magnet.What is an endothermic change?An endothermic change is a change in which heat energy is absorbed from the surroundings, such as when dissolving ammonium chloride in water.What is an exothermic change?An exothermic change is a change in which heat energy is evolved or released into the surroundings, such as during the burning of fuels.Why is the digestion of food classified as a chemical change?Digestion is a chemical change because complex food items are broken down by enzymes into simpler substances with completely different chemical compositions.
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Chapter: 02. Physical And Chemical Changes
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