Class 7 Science Chapter 5: Changes Around Us: Physical and Chemical (Hinglish Notes)

Ye chapter kis baare mein hai?

Chapter chaar students se shuru hota hai jo bataate hain unhone kya dekha: aadhe ghante mein paani ban gaya baraf ka tukda, raat bhar mein phool ban gayi gulaab ki kali, thande paani ki bottle jo ab thandi nahi rahi, aur kela jismein aur bhoore daag aur tez gandh aa gayi. Aise badlaav hamaare chaaron or hote hain, aur hum unhe dekhkar, soonghkar, chhookar, sunkar aur chakhkar pehchaante hain. Chapter poochta hai ki kya inhe kuch prakaar mein baanta ja sakta hai, aur do mukhya prakaar paata hai: physical aur chemical.

Physical changes

Kaagaz ki naav banaakar khol do: wahi kaagaz waapas milta hai. Gubbaare ki hawa nikaal do: wahi rubber hai. Chalk peeskar powder banao: vo ab bhi chalk hai, bas chhote tukdon mein. Paani bhi solid, liquid ya gas ho sakta hai aur in avasthaon ke beech badalta hai. Har baar roop badalta hai, par koi naya padaarth nahi banta. Jab sirf aakaar, size ya avastha jaisi physical properties badlein, to use physical change kehte hain. Padho physical aur chemical changes.

Chemical changes

Straw se nal ke paani mein phoonk maaro to sirf bulbule bante hain. Lime water mein phoonk maaro to vo doodhiya ho jaata hai; kuch der rakhne par neeche ek safed solid baith jaata hai. Kuch naya bana hai. Jo badlaav ek ya zyaada naye padaarth banaaye, vo chemical change hai, aur jis prakriya se ve bante hain use chemical reaction kehte hain. Yahan hamaari saans ki carbon dioxide lime water (calcium hydroxide) ke saath reaction karke calcium carbonate banaati hai, ek safed padaarth jo paani mein nahi ghulta, aur thoda paani. Reaction ko chhote mein chemical equation se likh sakte hain, aur lime water ka doodhiya hona carbon dioxide ki jaanch hai.

Sirke ya nimbu ke ras mein thoda baking soda (sodium hydrogen carbonate) daalo to jhaag aur bulbule bante hain. Ye gas taaze lime water se guzre to use doodhiya kar deti hai, isliye ye carbon dioxide hai: sirka + baking soda → carbon dioxide + doosre padaarth. Saade paani mein baking soda bina bulbulon ke bas ghul jaata hai.

Jang aur combustion

Lohe mein jang lagne par ek naya bhoora padaarth, jang (iron oxide), banta hai, isliye jang lagna chemical change hai. Magnesium ribbon chakaachaundh roshni ke saath jalta hai aur safed powder, magnesium oxide, chhodta hai: magnesium + oxygen → magnesium oxide + garmi + roshni. Jab koi padaarth oxygen ke saath reaction karke garmi aur/ya roshni de, to us reaction ko combustion kehte hain, aur is tarah jalne waale padaarth, jaise lakdi, kaagaz, cotton aur kerosene, combustible padaarth hain. Glass ke tumbler se dhaki mombatti jaldi bujh jaati hai, kyunki jalne ko oxygen chahiye; phir plate ka lime water doodhiya hota hai, jo dikhata hai ki wax ke carbon aur hawa ki oxygen se carbon dioxide bani. Jugnu bhi chemical change se roshni dete hain, par bina garmi ke: ise bioluminescence kehte hain.

Ignition temperature aur fire triangle

Kaagaz saalon hawa mein pada rahe to bhi nahi jalta. Jalti maachis ki teeli use lagbhag turant jala deti hai, aur magnifying glass se ikattha ki gayi dhoop use pehle dhuaan aur phir aag deti hai, bina kisi lau ke. Kaagaz tab jalta hai jab vo kaafi garam ho jaaye. Jis sabse kam taapmaan par koi padaarth aag pakade, vo uska ignition temperature hai. Isliye combustion ko teen cheezein chahiye, yaani fire triangle: combustible padaarth ya fuel, oxygen, aur itni garmi jo fuel ko ignition temperature tak le jaaye. Isiliye jis insaan ke kapdon mein aag lage, us par kambal lapetne se aag bujh jaati hai: hawa ruk jaati hai. Synthetic kambal kabhi use mat karo, vo pighalkar twacha se chipak sakta hai. Padho combustion kya hai.

Ek hi prakriya mein dono

Jalti mombatti mein dono tarah ke badlaav hain. Lau ki garmi wax ko pighaalti hai, jo batti pe chadhkar vaashp banta hai; neeche tapakta pighla wax phir jam jaata hai. Ye physical changes hain. Phir wax ki vaashp jalkar lau banaati hai, jo chemical change hai. Scientist Michael Faraday ko mombatti itni achhi shuruaat lagi ki unnisvi sadi mein unhone The Chemical History of a Candle naam se mashhoor lectures diye, pighalne, vaashp banne aur combustion par.

Kya badlaav ulte ho sakte hain?

Kuch badlaav ulte ho sakte hain: pighli baraf phir jamaai ja sakti hai, aur bhaap bana paani phir se paani banaaya ja sakta hai. Kuch nahi ho sakte: kati sabziyan apne purane size aur aakaar mein waapas nahi aa saktin, aur popcorn phir makka nahi banta. Badlaav chahe gaye bhi ho sakte hain, jaise doodh se dahi, phal ka pakna aur khaana pakna, ya anchahe, jaise lohe mein jang aur rakha khaana sadna. Ek hi badlaav dono ho sakta hai: sadna khaana kharaab karta hai, par rasoi ke kachre se compost bhi banaata hai. Insaanon ke kuch badlaavon ka asar lamba hota hai: gaadiyon mein zyaada fuel jalne se hawa mein carbon dioxide badhti hai, aur sookhta paint aise padaarth chhodta hai jo hawa ko pradooshit karte hain. Padho reversible aur irreversible changes kya hain.

Dheeme praakritik badlaav

Pahaadon ki talhati mein ret, mitti aur pattharon ke dher, jinhe sediments kehte hain, chattaanon ke tootne se bante hain. Taapmaan ke badlaav, badhti jadein aur daraaron mein jamta paani chattaanon ko physical tareeke se todte hain, jabki paani aur hawa unhe chemical tareeke se badal sakte hain: lohe waali kaali basalt chattaan par iron oxide ki laal parat ban sakti hai. Ye saare badlaav milkar weathering hain, aur dheere-dheere mitti banaate hain. Erosion hawa aur behte paani se kankad, mitti aur sediments ka le jaaya jaana hai, ek physical change; nadi ke kankad chikne ho jaate hain, aur jahan paani dheema hota hai wahan sediments baithkar hazaaron saalon mein nayi chattaan ban jaate hain.

Saar mein

Physical change sirf physical properties badalta hai; chemical change naye padaarth banaata hai aur equation se likha ja sakta hai. Combustion, khaana pakaana aur jang chemical changes hain, aur aag ko fuel, oxygen aur garmi chahiye. Badlaav ulta ho bhi sakta hai aur nahi bhi, chaha bhi ho sakta hai aur anchaha bhi, aur dheeme praakritik badlaav chattaanon ko mitti banaate hain. Har activity aur sawaal ke jawaab Chapter 5 ke NCERT solutions mein hain.