Questions: Particulate nature of matter

Q1. How does grinding chalk show that matter is made of tiny particles?

Answer (English): When chalk is broken and ground into powder, every speck is still chalk, because only the size of the pieces changes and grinding is a physical change. If the powder could be broken further and further, we would finally reach the basic units of chalk, its constituent particles. The fact that a whole stick of chalk is built from these units shows that matter is composed of a very large number of extremely small particles.

Hinglish: Chalk ko todkar peesne par bhi har tukda chalk hi rehta hai; sirf size chhota hota hai, substance nahi badalta, kyunki grinding physical change hai. Aur zyada peesne par aakhir mein chalk ki basic units milengi, jinhe constituent particles kehte hain. Ek chalk stick aise bahut saare chhote particles se bani hai, isliye matter particles ka bana hota hai.

Q2. What are constituent particles and interparticle spaces? Explain with the sugar-and-water example.

Answer (English): A constituent particle is the smallest unit from which a larger piece of a substance is built. The gaps between these particles are called interparticle spaces. When sugar is stirred into water, it breaks into particles too small to see, and these particles occupy the spaces between the water particles. The water tastes sweet everywhere, and no sugar particles are visible, which shows that matter is made of tiny units with empty spaces between them.

Hinglish: Constituent particle kisi substance ke bade tukde ki basic unit hai. In particles ke beech ki khaali jagah ko interparticle spaces kehte hain. Sugar ko paani mein milaane par woh itne chhote particles mein badal jaati hai ki dikhti nahi, aur ye particles paani ke particles ke beech ki jagah mein chale jaate hain. Paani har jagah meetha lagta hai par sugar ke particles dikhte nahi, jo dikhata hai ki matter chhote particles aur unke beech khaali spaces se bana hai.

Q3. Compare the arrangement, attraction and movement of particles in solids, liquids and gases.

Answer (English): In solids, particles are packed most closely, the attractions are strongest, and the particles are fixed in place so they only vibrate. In liquids, particles are a little farther apart, the attractions are weaker than in solids, and the particles can move within a limited space. In gases, the spacing is largest, the attractions are negligible, and the particles move freely in all directions. This ordering of spacing and attraction explains the different shapes and volumes of the three states. Spacing and attraction therefore vary in the same order: least in solids, more in liquids, most in gases.

Hinglish: Solid mein particles sabse paas, attraction sabse strong, aur particles fixed jagah par sirf vibrate karte hain. Liquid mein particles thode door, attraction solid se kam, aur particles limited space mein move kar sakte hain. Gas mein spacing sabse zyada, attraction negligible, aur particles har direction mein free move karte hain. Isi wajah se teeno states ka shape aur volume alag hota hai.

Q4. Why do solids have a definite shape and volume? What happens to their particles on heating?

Answer (English): In a solid, the interparticle attractions are strong and the particles are tightly packed in fixed positions, so the solid keeps its shape and volume. Heating makes the particles vibrate more vigorously. At the melting point, the vibrations become strong enough for the particles to leave their fixed positions, the attractions are weakened, and the solid changes into a liquid. Solids with weak attractions melt at lower temperatures than those with strong attractions.

Hinglish: Solid mein interparticle attraction strong hota hai aur particles fixed positions par tightly packed hote hain, isliye solid ka shape aur volume fixed rehta hai. Heating par particles zyada zor se vibrate karte hain. Melting point par vibrations itni strong ho jaati hain ki particles apni fixed jagah chhod dete hain, attraction kamzor hoti hai, aur solid liquid ban jaata hai. Kam attraction wale solids kam temperature par pighalte hain.

Q5. Why do liquids have a fixed volume but no fixed shape?

Answer (English): The particles of a liquid are close together, so the liquid keeps the same volume when poured from one container to another. However, the particles are not fixed in place; they can move around within the liquid. This is why the liquid takes the shape of whatever container holds it. Moving a finger through water shows the same thing: the water is pushed aside and flows back, without a permanent hole.

Hinglish: Liquid ke particles paas-paas hote hain, isliye ek container se doosre mein daalne par volume same rehta hai. Par particles fixed jagah par nahi hote; woh liquid ke andar move kar sakte hain. Isliye liquid jis container mein ho usi ka shape le leta hai. Paani mein ungli chalane par paani hat kar wapas aa jaata hai, koi pakka chhed nahi banta.

Q6. Why do gases have no fixed shape or volume? Describe the smoke-jar activity.

Answer (English): Gas particles move freely in all directions and the attractions between them are negligible, so a gas spreads out to fill whatever space is available. In the activity, smoke is trapped in one jar, the jar is covered with a glass plate and a second jar is placed above it. When the plate is removed, the smoke spreads into the second jar and fills it. This shows that gases have neither a fixed shape nor a fixed volume.

Hinglish: Gas ke particles har direction mein free move karte hain aur attraction negligible hoti hai, isliye gas jitni jagah mile use bhar deti hai. Activity mein ek jar mein dhuan bhara, uske upar glass plate aur doosra jar rakha; plate hatate hi dhuan doosre jar mein phail kar use bhar deta hai. Isse pata chalta hai ki gas ka na shape fixed hota hai na volume.

Q7. What does the syringe test show about interparticle spaces? Why does the water level change when sugar dissolves?

Answer (English): In the syringe test, air can be compressed because gas particles have large spaces between them; water cannot be compressed much because its particles are already close together. This shows that the interparticle spaces are largest in gases and smaller in liquids and solids. When sugar is added to water, the level rises, but after the sugar dissolves the level is lower than the new mark, because sugar particles move into the spaces between water particles. The solution's volume is smaller than the two volumes added together.

Hinglish: Syringe test mein hawa compress ho jaati hai kyunki gas particles ke beech zyada space hota hai; paani compress nahi hota kyunki uske particles already paas hote hain. Isse pata chalta hai ki interparticle spaces gases mein sabse zyada hote hain. Sugar daalne par paani ka level badhta hai, par ghulne ke baad naye mark se neeche aa jaata hai, kyunki sugar ke particles paani ke particles ke beech ki jagah mein chale jaate hain. Solution ka volume dono ke volume ke sum se kam hota hai.

Q8. What is diffusion? How does temperature affect it?

Answer (English): Diffusion is the spreading of particles from a region of higher concentration to one of lower concentration because the particles are in constant motion. When a grain of potassium permanganate is dropped into water, its pink colour spreads until the whole glass is uniform, and an incense stick's fragrance reaches every corner of a room. In the temperature test, the colour spreads fastest in hot water, more slowly at room temperature and slowest in ice-cold water, because heating increases the movement of particles.

Hinglish: Diffusion matlab particles ka zyada concentration wali jagah se kam concentration wali jagah tak phailna, kyunki particles constantly move karte hain. Potassium permanganate ka grain paani mein daalne par uska pink colour poore glass mein phail jaata hai, aur incense ki khushbu kamre ke har kone tak pahunchti hai. Temperature test mein colour garam paani mein sabse tez, room temperature par dheere, aur ice-cold paani mein sabse dheere phailta hai, kyunki heat se particle movement badhti hai.

Q9. How does thermal energy decide whether a substance is a solid, a liquid or a gas?

Answer (English): Thermal energy is the energy of motion of the particles. In a solid, thermal energy is low, so particles stay close and only vibrate. At the melting point, added energy overcomes the attractions enough for particles to leave their fixed positions, and the substance becomes a liquid. In a gas, the particles carry enough energy to break the attractions completely and move with full freedom in all directions.

Hinglish: Thermal energy particles ki motion ki energy hai. Solid mein thermal energy kam hoti hai, isliye particles paas rehte hain aur sirf vibrate karte hain. Melting point par di gayi energy attraction par kaabu paane ke liye kaafi hoti hai, particles fixed jagah chhod dete hain aur liquid ban jaate hain. Gas mein particles ke paas itni energy hoti hai ki woh attraction ko poori tarah cross karke har direction mein free ghoomte hain.

Q10. Why do gases mix readily but solids hardly mix?

Answer (English): Gases mix readily because their particles move freely in all directions and the attractions between them are negligible, so particles of one gas can spread through the space occupied by another. In solids, particles are held in fixed positions by strong attractions and can only vibrate, so a solid cannot flow into another solid and mix by particle movement. Diffusion is therefore fast in gases and very slow in solids.

Hinglish: Gases aasani se milti hain kyunki unke particles har direction mein free move karte hain aur attraction negligible hoti hai, isliye ek gas ke particles doosri gas ki jagah mein phail jaate hain. Solids mein particles strong attraction se fixed hote hain aur sirf vibrate karte hain, isliye solid doosre solid mein beh kar mix nahi ho sakta. Isliye diffusion gases mein tez aur solids mein bahut dheema hota hai.

The quick check below has five multiple choice questions on the particulate nature of matter, the three states and diffusion. Each one comes with a short explanation, so take the quiz and see which topics need another read.