Samacheer Kalvi Class 6 Science Solutions Term 2 Chapter 3 Changes Around Us

I. Choose The Correct Answer

Question 1. When ice melts to form water, change occurs in its
(a) position
(b) colour
(c) state
(d) composition
Answer: (c) state
In simple words: When ice turns into water, its physical form changes from solid to liquid. This is called a change of state.

🎯 Exam Tip: Remember that melting, freezing, boiling, and condensation are all examples of changes in state.

Question 2. Drying of wet clothes in air is an example of
(a) Chemical change
(b) Undesirable change
(c) irreversible change
(d) physical change
Answer: (d) physical change
In simple words: When clothes dry, water simply evaporates and goes into the air, but the clothes themselves do not change into a new substance. This makes it a physical change.

🎯 Exam Tip: Physical changes alter a substance's appearance but not its chemical composition; chemical changes form new substances.

Question 3. Drying of wet clothes in air Is an example of
(a) Chemical change
(b) Undesirable change
(c) irreversible change
(d) physical change
Answer: (d) physical change
In simple words: Drying clothes means the water turns into vapor and leaves the clothes, but the clothes remain the same material. So, it's a physical change.

🎯 Exam Tip: Recognizing whether a new substance is formed is key to distinguishing physical from chemical changes.

Question 4. Out of the following an example of a desirable change is
(a) rusting
(b) change of seasons
(c) earthquake
(d) flooding
Answer: (b) change of seasons
In simple words: Desirable changes are those that are useful or good for us. The change of seasons brings variety and allows for different crops to grow, which is helpful.

🎯 Exam Tip: Think about the impact of each change on humans and the environment to decide if it's desirable or undesirable.

Question 5. Air pollution leading to Acid rain is a
(a) reversible change
(b) fast change
(c) natural change
(d) human made change
Answer: (d) human made change
In simple words: Acid rain is caused by pollution from human activities like burning fuels. This makes it a change created by people, not by nature alone.

🎯 Exam Tip: Distinguish between changes caused by natural processes (like weather) and those resulting from human actions (like pollution).

II. Fill In The Blanks

Question 1. Magnet attracts iron needle. This is ........... change, (a reversible / an irreversible)
Answer: a reversible
In simple words: A magnet attracting an iron needle is a reversible change because you can easily separate them again without changing either material. The needle does not turn into a magnet permanently.

🎯 Exam Tip: A change is reversible if you can get the original substance back easily.

Question 2. Boiling of egg results in ........... change, (a reversible / an irreversible)
Answer: an irreversible
In simple words: Once an egg is boiled, you cannot make it raw again. This means the change is permanent and cannot be undone.

🎯 Exam Tip: Changes that create new substances or cannot be undone are usually irreversible.

Question 3. Changes that are harmful to us are ........... (desirable / undesirable)
Answer: undesirable
In simple words: Changes that cause harm or are not wanted are called undesirable changes. These changes usually have a negative impact.

🎯 Exam Tip: Classify changes as desirable or undesirable based on their benefits or harm to living things and the environment.

Question 4. Plants convert Carbon-di-oxide and water into starch. This is an example of ........... change, (natural / human made)
Answer: Natural
In simple words: Photosynthesis, where plants make food from carbon dioxide and water, is a process that happens all the time in nature without human help. It's an essential natural process.

🎯 Exam Tip: Natural changes occur without human intervention, while human-made changes are caused by human activities.

Question 5. Bursting of fire crackers is a ........... change whereas germination of seeds is a ........... change, (slow / fast)
Answer: fast; slow
In simple words: Firecrackers burst very quickly, in a moment. Seed germination, on the other hand, takes many days to weeks, showing a much slower change.

🎯 Exam Tip: Differentiate between fast and slow changes by considering the time scale over which they occur.

III. True Or False. If False, Give The Correct Statement

Question 1. Growing of teeth in an infant is slow change.
Answer: True
In simple words: A baby's teeth grow over many months, not quickly. This is indeed a slow change.

🎯 Exam Tip: Many biological growth processes, like teeth or hair growth, are examples of slow changes.

Question 2. Burning of match stick is a reversible change.
Answer: False – It is an irreversible change
In simple words: Once a matchstick burns, it turns into ash and smoke, and you cannot get the original matchstick back. This makes it a permanent change.

🎯 Exam Tip: Burning is a classic example of an irreversible chemical change because new substances are formed.

Question 3. Change of New moon to Full moon is human made.
Answer: False – It is a Natural change
In simple words: The moon's phases, from new moon to full moon, are caused by its orbit around the Earth and the sun's light. Humans do not create this change.

🎯 Exam Tip: Celestial events and weather patterns are typically natural changes.

Question 4. Digestion of food is a physical change.
Answer: False – It is a Chemical change
In simple words: When we digest food, our body breaks it down into different, simpler substances using chemicals. This chemical breakdown is essential for nutrient absorption.

🎯 Exam Tip: Digestion involves chemical reactions, where complex food molecules are broken into simpler ones, making it a chemical change.

Question 5. In a solution of salt in water, water is the solute.
Answer: False - Water is the solvent
In simple words: In a solution, the solvent is what does the dissolving, and it's usually present in a larger amount. Water dissolves the salt, so water is the solvent.

🎯 Exam Tip: Remember that the substance being dissolved is the solute, and the substance doing the dissolving is the solvent.

IV. Analogy

Question 1. Curdling of milk : irreversible change :: Formation of clouds : ........... change
Answer: reversible
In simple words: You cannot un-curdle milk once it's spoiled, but water vapor can form clouds and then turn back into rain, which is a reversible process.

🎯 Exam Tip: Consider if the original state can be recovered to determine if a change is reversible or irreversible.

Question 2. Photosynthesis : ........... change :: burning of coal : Human – made change
Answer: Natural
In simple words: Photosynthesis is a process that happens naturally in plants. Burning coal is done by humans for energy, making it a human-made change.

🎯 Exam Tip: Classify changes based on whether they occur in nature or are initiated by human activities.

Question 3. Dissolving of glucose: reversible change :: Digestion of food : ........... change
Answer: Irreversible
In simple words: You can get glucose back by evaporating the water, but once food is digested into simpler chemicals, you cannot turn it back into its original form.

🎯 Exam Tip: If new substances are formed and the process cannot be easily reversed, it's typically an irreversible change.

Question 4. Cooking of food : desirable change :: decaying of food : .............change
Answer: undesirable
In simple words: We cook food to make it taste good and safe, which is a desirable change. But food decay means it spoils and becomes unusable, which is undesirable.

🎯 Exam Tip: Evaluate changes from a human perspective to determine if they are desirable (beneficial) or undesirable (harmful).

Question 5. Burning of matchstick: ............ change :: Rotation of the Earth : Slow change
Answer: Fast
In simple words: A matchstick burns in a very short time, which is fast. The Earth's rotation, which causes day and night, is a continuous and much slower process in comparison.

🎯 Exam Tip: Compare the duration of different processes to distinguish between fast and slow changes.

V. Circle The Odd One Out. Give Reason For Your Choice

Question 1. Growth of a child, Blinking of eye, Rusting, Germination of a seed.
Answer: Blinking of eye (a fast change)
In simple words: Blinking happens very quickly. Growth of a child, rusting, and seed germination all take a long time to happen, making them slow changes.

🎯 Exam Tip: When identifying the odd one out, look for a common characteristic among most items and how one item differs.

Question 2. Glowing of a bulb, lighting of a Candle, breaking of a coffee mug, curdling of milk.
Answer: Curdling of milk (a chemical change)
In simple words: Glowing a bulb, lighting a candle (melting wax is physical, burning wick is chemical, but the overall context leans to physical change of light/heat), and breaking a mug are mainly physical changes. Curdling milk is a chemical change because new substances are formed.

🎯 Exam Tip: Pay attention to whether new substances are formed or if only the form/appearance changes to distinguish between chemical and physical changes.

Question 3. Rotting of an egg, condensation of water vapour, trimming of hair, Ripening of fruit.
Answer: Trimming of hair (Man-made change)
In simple words: Rotting of an egg, condensation, and ripening of fruit are all natural processes. Trimming hair is an action done by a person, so it is human-made.

🎯 Exam Tip: Consider the agent or cause of the change (natural forces vs. human action) to categorize it correctly.

Question 4. Inflating a balloon, popping a balloon, fading of wall paint, burning of kerosene
Answer: Burning of Kerosene (Chemical change)
In simple words: Inflating and popping a balloon, and paint fading are physical changes or processes that don't create new substances. Burning kerosene, however, produces new substances like carbon dioxide and water, making it a chemical change.

🎯 Exam Tip: The formation of new substances (like ash, gas, or a change in color due to chemical reaction) is a strong indicator of a chemical change.

VI. Give A Very Short Answer

Question 1. What kind of change is associated with the decaying of plants?
Answer: Decaying of plants is associated with slow change and chemical change. Dead plants break down over time into simpler substances. This process is important for the soil.
In simple words: When plants decay, it's a slow and chemical change, as they break down into new materials.

🎯 Exam Tip: Remember that decomposition (decay) involves chemical reactions and typically occurs over a period, making it a slow process.

Question 2. You are given some candle wax. Can you make a candle doll from it? What kind of change is this?
Answer: Yes, I can make a doll from the candle. The kind of change is a physical change. You can melt the wax and reshape it without changing what the wax is made of.
In simple words: Yes, you can make a doll from candle wax. This is a physical change because the wax itself doesn't turn into a new material.

🎯 Exam Tip: Reshaping a substance, like melting and molding wax, is a physical change as its chemical properties remain the same.

Question 3. Define a slow change.
Answer: Changes which take place over a long period of time (hours/days/months/years) are known as slow changes. These changes are often gradual and not easily observed happening in real-time.
In simple words: A slow change is something that takes a long time, like hours, days, or even years, to happen.

🎯 Exam Tip: Give examples like rusting or growth of a tree to illustrate your definition of a slow change.

Question 4. What happens when cane sugar is strongly heated? Mention any two changes in it.
Answer: When Cane sugar is strongly heated, it will initially melt and after that start to decompose. It will turn brown and then black and give off fumes. This process is called caramelization and eventually carbonization. The changes involved are:
1. Physical change
2. irreversible change
In simple words: When sugar is heated strongly, it first melts, then turns brown and black, giving off smoke as it breaks down. These changes are physical (melting) and irreversible (decomposition).

🎯 Exam Tip: Heating sugar involves both physical (melting) and chemical (decomposition) changes, with the chemical change being irreversible.

Question 5. What is the solution?
Answer: When a solute is dissolved in a solvent, it forms a solution. A solution is a uniform mixture where one substance is completely dissolved in another. Solute + solvent \( \rightarrow \) solution.
In simple words: A solution is made when one substance (solute) completely mixes into another (solvent).

🎯 Exam Tip: Remember that in a solution, the solute is the substance that dissolves, and the solvent is the substance in which it dissolves.

VII. Give A Short Answer

Question 1. What happens when the paper is burnt? Explain.
Answer: When the paper is burnt, oxygen from the air combines with carbon in the paper turning into carbon dioxide and water vapor which float away, leaving solid ash. The action of burning paper can't be reversed. So, it is an irreversible change. Also, it is a Chemical change and a Fast change. Burning always produces new substances.
In simple words: When paper burns, it combines with air to make new things like ash and gases. You cannot get the paper back, so it's a fast, irreversible chemical change.

🎯 Exam Tip: Burning is a key example of a chemical change that is irreversible and usually fast, producing new substances.

Question 2. Can deforestation be considered a desirable change? Explain.
Answer:
1. Deforestation cannot be considered a desirable change.
2. Because it is harmful to our environment and not desired by us are known as Undesirable changes. Deforestation leads to soil erosion, loss of biodiversity, and climate change.
In simple words: No, deforestation is not desirable. It harms the environment by causing problems like less rainfall, soil erosion, and loss of animal homes.

🎯 Exam Tip: Focus on the negative impacts of deforestation, such as environmental degradation and loss of resources, to explain why it's undesirable.

Question 3. What type of changes is associated with the germination of a seed? Explain.
Answer:
1. Germination of seed is a slow change.
2. Changes which take place over a long period of time (days) are known as Slow changes. During germination, the seed also undergoes chemical changes as stored food is converted for growth.
In simple words: Seed germination is a slow change because it takes many days for the seed to grow. It also involves chemical changes as the seed develops.

🎯 Exam Tip: Remember that biological processes like germination are generally slow and involve complex chemical transformations.

VIII. Answer In Detail

Question 1. Give one example in each case that happens around you.
(a) Slow and fast change
(b) Reversible and irreversible change
(c) Physical and chemical change
(d) Natural and man-made change
(e) Desirable and undesirable change
Answer:

🎯 Exam Tip: When asked for examples, ensure they are distinct and clearly illustrate the specific type of change being asked for.

IX. Questions Based On Higher Order Thinking Skills (Hots)

Question 1. When a candle is lit the following changes are observed.
1. Wax melts.
2. Candle keeps burning.
3. The size of the candle decreases.
4. The molten wax solidifies
Answer: The changes observed when a candle is lit include:
1. Wax melts: This is a physical change as solid wax turns into liquid wax.
2. Candle keeps burning: The wick burns, and the wax vaporizes and burns, producing light and heat. This is a chemical change.
3. The size of the candle decreases: This is a physical change due to the consumption of wax.
4. The molten wax solidifies: This is a physical change as liquid wax cools and becomes solid again.
In simple words: When a candle burns, the wax melts (physical change), the candle gets smaller, and the wax turns solid again (physical changes). But the burning of the wick and wax vapor is a chemical change, making new substances like smoke.

🎯 Exam Tip: Candle burning is a good example of how both physical (melting, solidifying, size decrease) and chemical (burning of wick and wax vapor) changes can happen at the same time.

Question 2. Which of the changes can be reversed? Justify your answer.
Answer: When the candle is burning, the heat of the flame melts the solid wax to liquid wax. This signifies reversible (or) Physical changes. Also, as the wax melts, the size of candle decreases. If then molten wax solidifies and takes a different shape. The melting and solidifying of wax are reversible because the wax itself does not change its chemical nature.
In simple words: The melting of the wax into liquid and then its solidifying back into solid wax are reversible changes. You can always get the wax back in its original chemical form, even if the shape changes.

🎯 Exam Tip: Differentiate between the melting/solidifying of wax (physical, reversible) and the actual burning of wax/wick (chemical, irreversible).

I. Choose The Appropriate Answer

Question 1. Water changes into ice on cooling are called as
(a) Melting
(b) Vaporisation
(c) Condensation
(d) Freezing
Answer: (d) Freezing
In simple words: When water gets cold enough to turn into ice, this process is called freezing. It's when a liquid becomes a solid.

🎯 Exam Tip: Understand the specific terms for phase changes: melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), condensation (gas to liquid), and sublimation (solid to gas).

Question 2. ........... is the process in which something becomes different from what it was earlier.
(a) Classification
(b) Composition
(c) Position
(d) Change
Answer: (d) Change
In simple words: Change is simply when something alters or transforms from its previous state or form. It describes any alteration in an object or substance.

🎯 Exam Tip: The term "change" is a broad concept covering any alteration in a substance or object.

Question 3. Evaporation of water from lakes and river
(a) Slow change
(b) Fast change
(c) Natural change
(d) Both (a) and (b)
Answer: (d) Both (a) and (b)
In simple words: Water evaporation from large bodies like lakes is generally a slow, continuous process, but it is also a natural process that happens without human involvement.

🎯 Exam Tip: Some changes can fit into multiple categories, like evaporation being both a natural and a slow (or sometimes fast, depending on conditions) physical change.

Question 4. ........... change is a temporary change
(a) Physical
(b) Chemical
(c) Undesirable
(d) slow
Answer: (a) Physical
In simple words: Physical changes, like melting ice, are temporary because the substance can usually go back to its original form easily. No new substance is created.

🎯 Exam Tip: The key feature of a physical change is that it is often temporary and reversible, without forming new chemical identities.

Question 5. The blackening of the Silver anklet is a (an)
(a) Irreversible change
(b) Temporary change
(c) Short term change
(d) Periodical change
Answer: (a) Irreversible change
In simple words: Silver blackens due to a chemical reaction with sulfur in the air, forming silver sulfide. This new substance is hard to reverse, making it an irreversible change.

🎯 Exam Tip: Tarnishing of silver is a chemical change because a new compound (silver sulfide) is formed on the surface, which is difficult to reverse completely.

II. Fill In The Blanks

Question 1. A change in which a new substance is formed is called ...........
Answer: Chemical Change
In simple words: When a substance changes into something completely different, it's called a chemical change.

🎯 Exam Tip: The defining characteristic of a chemical change is the formation of one or more new substances.

Question 2. Formation of coal is a ...........
Answer: Slow Change
In simple words: Coal takes millions of years to form from dead plants, making it a very slow process.

🎯 Exam Tip: Geological processes like the formation of fossil fuels are classic examples of extremely slow changes.

Question 3. An example of natural as well as an undesirable change is ...........
Answer: Earthquake
In simple words: An earthquake is a natural event that we do not want because it causes a lot of damage and harm. It is a natural and undesirable event.

🎯 Exam Tip: Natural disasters like earthquakes and tsunamis are examples of changes that are both natural and undesirable.

Question 4. ........... is the Universal Solvent.
Answer: Water
In simple words: Water is known as the universal solvent because it can dissolve more substances than any other liquid.

🎯 Exam Tip: Water's ability to dissolve many different substances makes it crucial for biological and chemical processes.

Question 5. Eco-friendly changes are ...........
Answer: Desirable changes
In simple words: Changes that are good for the environment are called eco-friendly, and these are always desirable because they help nature.

🎯 Exam Tip: Desirable changes benefit either humans or the environment, often both.

III. Match The Following

Question. Match the following.

🎯 Exam Tip: For matching questions, understand the core definition of each term to correctly pair them with examples.

IV. Analogy

Question 1. Rusting of Iron : undesirable change : : Dead plants turn into manure : ...........
Answer: Desirable change
In simple words: Rusting is harmful and unwanted. But dead plants becoming manure is good because it makes the soil rich and helps new plants grow.

🎯 Exam Tip: Analogies test your ability to find similar relationships between different pairs of concepts.

Question 2. Touch me not plant: ........... : : digestion of food : Irreversible change
Answer: Reversible change
In simple words: The touch-me-not plant's leaves close when touched but open up again later, showing a reversible change. Food digestion, however, cannot be undone once it breaks down into new substances.

🎯 Exam Tip: Focus on whether the original state can be restored when classifying changes as reversible or irreversible.

Question 3. Change of seasons : slow change : : Breaking of glass : ...........
Answer: fast change
In simple words: Seasons change slowly over months. Breaking glass happens in an instant, which is a very fast change.

🎯 Exam Tip: Consider the time taken for each change to occur when categorizing them as slow or fast.

Question 4. Earth quake : undesirable change : : Heartbeat: ...........
Answer: desirable change
In simple words: Earthquakes cause harm, so they are undesirable. A heartbeat is necessary for life and keeps us alive, so it is a desirable change.

🎯 Exam Tip: Assess the positive or negative impact of a change to determine if it is desirable or undesirable.

Question 5. Silver articles turning black .............Boiling of H2O : physical change
Answer: Chemical change
In simple words: When silver turns black, it is a chemical reaction. Boiling water is a physical change because water just changes its state from liquid to gas, but it's still water.

🎯 Exam Tip: Tarnish on silver indicates a chemical reaction, while boiling water is a physical change of state.

V. Very Short Answer

Question 1. What is the change?
Answer: Change is the observable difference between the initial state and the final state of any substance. It describes any alteration in a substance's properties, form, or composition.
In simple words: A change is when something looks different or acts different from how it was before.

🎯 Exam Tip: A good definition of "change" highlights the difference between an initial and a final state.

Question 2. What is a reversible change?
Answer: Changes which can be reversed (to get back to the original state) are known as reversible changes. This means the substance can return to its first form without permanent alteration.
In simple words: A reversible change is when you can easily turn something back to how it was at the start.

🎯 Exam Tip: Always provide an example like melting ice or dissolving sugar to illustrate a reversible change.

Question 3. What is melting? Give example.
Answer: The conversion of a solid into a liquid by heating is called melting. Ex.: Ice into water. This process occurs when a substance absorbs enough energy to break its rigid solid structure.
In simple words: Melting is when a solid turns into a liquid because it gets warmer, like ice turning into water.

🎯 Exam Tip: Clearly state that melting requires heat and is the transition from solid to liquid, providing a common example.

Question 4. Water is the universal solvent. Why?
Answer: Water is known as the universal solvent. It dissolves a wide range of substances. Its unique chemical structure allows it to interact with and dissolve many different types of compounds.
In simple words: Water can dissolve many different things, more than any other liquid, so we call it the universal solvent.

🎯 Exam Tip: Explain that water's ability to dissolve many substances is why it's called the "universal solvent."

VI. Long Answer

Question 1. Distinguish between the physical and chemical changes.
Answer:

🎯 Exam Tip: When distinguishing between physical and chemical changes, focus on whether new substances are formed and if the change is reversible.

Question 2. Tabulate some changes taking place in our body system with its type.
Answer:

In simple words: Our bodies experience many types of changes, some are slow like growing hair, and others are fast like blinking our eyes. These various changes are essential for our body's functioning and overall health. Some changes can be reversed, while others, like digestion, cannot.

🎯 Exam Tip: When tabulating changes, clearly define each category and provide precise, relevant examples to ensure full marks.