The understandable notes- Chemical reaction and equations, Class 10, Part 1
Physical and Chemical Change
1. Physical Change
A physical change is a change in the shape, size, or state of a substance, but its composition remains the same. No new substance is formed.
( Ye to i think sabko pata ho hoga ki physical chage ya fir chemical change kisi kehte hai. Nahi pata to sun lo jab bhi kisi substance ki shape, size yar fir uske state mai koi change aata hai tab physical change hota hai. Physical change mai koi naya product form nahi hota. Jaise ladki kaat kr furniture bana diya. Ye generally nature mai reversible hote hai yani ki inhe dubara wapis usi state mai laya jaa sakta. Jaise ice melt hokar pani ban gayi aur pani ko freeze krke ice bana di. Badi ladki ko kaatkr chota bana diya aur fir use chipka kar bada bana diya. Kul milakar substance apni original form mai hi rehta hai.)
Examples:
Melting Ice: When ice melts into water, it changes its state from solid to liquid, but it is still water.
Tearing Paper: The paper is broken into pieces, but it is still paper.
Dissolving Sugar in Water: The sugar disappears in water, but it remains sugar (it can be separated by evaporation).
Key Features of Physical Change:
✔ No new substance is formed.
✔ It is usually reversible.
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2. Chemical Change
A chemical change is a change in which a new substance is formed with different properties.
Examples:
Burning Paper: When paper burns, it turns into ash and smoke. This is a new substance that cannot be changed back into paper.
Rusting of Iron: When iron reacts with air and water, it forms rust (iron oxide), which is a completely different substance.
Cooking Food: Raw vegetables and rice change their structure when cooked, forming new substances.
Key Features of Chemical Change:
✔ A new substance is formed.
✔ It is usually irreversible.
✔ It often involves heat, gas release, or color change.
( Ab dusre type ke change aate hai chemical change. To inme koi naya substance form hota hai. Aur ye nature mai bhi irreversible hote hai yani ki inhe dubara se original form mai nahi laya jaa sakta. Jaise doodh ki dahi bana di. Lakdi ko jala diya. Ye dhyan do ki lakdi ko jalana ek chemical change hai par metal to jalana ek physical change hai kyunki metal sirf apni state change krenge na ki properties. Ab cooking bhi chemical change hi hai. Ya fir lohe pr jang lag jana, fruits ka kharab ho jana ye sab chemical change hai.)
Chemical Reaction
Whenever a chemical change takes place, we say that a chemical reaction occurs. The key properties of a chemical reaction are given below:
- Change in state
- Change in color
- Evolution of a gas
- Change in temperature
Pehle wali ke liye samjho jaise hydrogen aur oxygen combine hokr water bana deti hai. Dono gases hai aur product liquid hai.
Cooper sulphate jiska colour blue hota hai jab usme iron mila diya jata hai to uska colour green ho jata hai.
Teesre wale to aise hi yaad rakh lo baki iske bhi kai examples hai. Jaise ki jab coal ko jalaya jata hai to CO2 release hoti hai.
Aur 4th wale ke liye thoda wait kre mai niche pura topic padhaunga.
Burning of magnesium
Burning of magnesium is a chemical change because it reacts with oxygen to form a new substance, magnesium oxide (MgO). This reaction is irreversible and produces heat and bright white light, indicating a chemical transformation. The properties of magnesium before and after burning are different—shiny metal turns into a white powder, confirming the change.
Before burning, magnesium needs to be cleaned because it forms a layer of magnesium oxide (MgO) or magnesium carbonate (MgCO₃) on its surface due to exposure to air. This layer prevents efficient burning, so magnesium is rubbed with sandpaper to remove it. Cleaning ensures a proper reaction with oxygen, allowing the metal to burn brightly and completely.
( Dekho ye aapki book mai likha hua hai isi liye batana jaruri hai. Ab jab bhi hum magnesium ko jalate hai tab wo ek kafi bright light ke sath jalta hai. Jise dekhna hai vo Mr. Indian Hacker ki video dekh sakta hai. Ab kamal ki baat hai ki agar magnesium mai aag lag rakhi hai aur aap uspar pani daalte ho to wo pani ki oxygen ko bhi chura leta hai aur aur tez jalne lagta hai. Agar uspr fire extinguisherska spray kroge to CO2 ki bhi oxygen chura lega. To ye magnesium jalkr form krta hai magnesium oxide, jo ki ek white powder hoti hai. Ab sari properties hi change ho gayi to hua na chemical reaction.
Ek aur baat aur ye question ncert mai bhi hai ki ise jalane se pehle saaf kyu krte hai. To magnesium kafi jyada reactive hota hai open environment mai aur ye kai baar oxygen se react krke ek magnesium oxide ki layer pehle hi apne upar chadha leta hai. Ab jab pehle se hi upar magnesium oxide ki layer hogi to jalega kaise. Bas isi liye ise pehle saaf krte hai.)
When zinc (Zn) reacts with dilute sulfuric acid (H₂SO₄), it produces zinc sulfate (ZnSO₄) and hydrogen gas (H₂).
Reaction:
Observations:
Zinc dissolves in sulfuric acid.
Bubbles of hydrogen gas are released.
The solution becomes colorless due to the formation of zinc sulfate (ZnSO₄).
This reaction is an example of a single displacement reaction, where zinc replaces hydrogen from sulfuric acid. The hydrogen gas produced can be tested by bringing a burning matchstick near it—it burns with a 'pop' sound.
(Ab is reaction ko bhi dekh lo. Jab zinc granules ko hum dilute sulphuric acid mai dalte hai tab zinc to sulfate ke sath react krke zinc sulphate bana leta hai aur hydrogen release hoti hai. Iske sath hi container ka temperature bhi increase ho jata hai. To yaha par gas bhi release ho gayi aur temperature bhi increase ho gaya to hua na ye bhi chemical reaction. Aur ye baat to pata hi hogi ki hydrogen hi release hui hai ye hum use jalakar check kr sakte hai kunki hydrogen burns with a pop sound.)
Chemical equation
A chemical equation is a way of representing a chemical reaction using symbols and formulas. It shows what substances react and what new substances are formed.
For example, when hydrogen reacts with oxygen to form water, we can write:
( Ab kisi bhi chemical reaction ko ya to statement ki form mai likho ya word equation ki ya fir chemical equation ki. Sabse aasan chemical equation hi hoti hai. Haan abhi shayad tumhe samajh nahi aaegi lekin hoti yehi hai. Koi nahi bas thoda time do ye chapter paaka krwa dunga.
Parts of a Chemical Equation
1. Reactants: The substances that react (left side of the equation).
Example: H₂ and O₂ in the above equation.
2. Products: The new substances formed (right side of the equation).
Example: H₂O (water) in the above equation.
3. Arrow ( → ): Means "reacts to form" or "yields".
( Yaar dekho isi mai teeno part samjha deta hu. Jo react hoga wo hoga reactant aur ledt hand side likha jayega. Yaad rakhna reactant react hoga. Jo banega vo hoga product jo ki right hand side likha jayega aur ek arrow hota hai jiski puinch normal arrow se thodi lambi hoti hai uska matlab hota hai reacts to form yani ki jo uski tail ki taraf honge vo honge reactants aur jiski taraf vo point krega wo honge product. Basic to ho gaya na clear ab baar krte hai balanced equation ki air ise likhne ke procedure ki.)
REACTANTS, PRODUCTS, ARROW
Reactants are the compounds or elements located on the left side of a chemical equation. These reactants are used in the reaction to form new products. During this process, they lose their original chemical properties and give rise to a new compound with different properties. For example, hydrogen and oxygen react to form water. While both hydrogen and oxygen are highly flammable gases, water is a liquid and resistant to fire. In this case, the reactants are gases, while the product is a liquid.
(Reactants naam se hi clear ho raha hai ki ye reaction ke liye use honge. Ab agar sabse jyada simple language mai batau to agar aap log matar paneer kha rahe ho to raw vegetables reactants hai. Matlab ki vo products jo further react hokr ek final product banate hai. Isme ek cheez ka dhyan rakhna kaafi important hai ki reactants compound bhi ho sakte hai aur elements bhi. Dhyan se samjho ki reactant ka kaam hota hai aapas mai ya fir kisi energy se react hokr final product banana. To ye baat kaafi jyada clear hai ki ye kuch bhi ho sakte hai jiase ki mere diye hue examples mai dono hi elements hai lekin final product ek compound hai water. Yaar dekho chemistry mai kaafi jyada chize yaad rakhni padtu hai lekin koi baat nahi 80 percent to mai samjha hi dunga. Haan to i hope ki reactants samajh aa gaya hoga aapko.)
Products are the final compounds or elements formed as a result of a chemical reaction between the reactants. The state of the product may or may not depend on the state of the reactants, and the properties of the product often differ from those of the reactants. Products are located on the right side of the chemical equation.
For example, when copper sulfate reacts with iron, they are reactants. During the reaction, iron sulfate is formed, and copper is displaced. In this case, copper and iron sulfate are the products.
CuSO₄ (aq) + Fe (s) → FeSO₄ (aq) + Cu (s)
(Ab jab reactants aapas mai react hokr ek naya compound banate hai to wo final product banta hai. Iska matlab ye hua ki jo final product hume kisi bhi reaction se milega use product hi kehte hai. Ab jaise ki is reaction mai cooper sulphate ka reaction jab iron se hota hai tab iron sulfate banta hai aur cooper separate ho jata hai to is case mai cooper sulfate aur iron reactants hai aur iron sulfate aur cooper products.)
The arrow (→) tells us the direction in which the reaction proceeds. The compounds or elements on the left side of the arrow are generally called reactants, and those on the right side are called products. A single arrow (→) represents an irreversible reaction, while a double arrow (⇌) represents a reversible reaction.
(Ab last part jo hume kisi equation mai samajhna hai vo hota hai arrow. To arrow hume ye btata hai ki reaction kis direction mai proceed kr raha hai jis taraf arrow ka face hota hai us taraf products hote hai aur jis taraf arrow ki tail hoti hai us taraf reactants. Aur jo reversible reaction hote hai unhe do arrow se represent kiya jaata hai.
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