1. How is a chemical change distinguished from a physical change chemi cal cha t
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Question
1. How is a chemical change distinguished from a physical change chemi cal cha that nes lan Ces hcacFion involues making o bonds between ato m 2. List fo ur kinds of observations that can lead you to conclude that a chemical change has tion is alten accompanied by eas and 1:ght , tLe lo-mak.on picc i pitat , tke. evolutio tance 3. How small of a change in temperature can you detect by touch? How could smaller changes in temperature be detected/ Soms aj these eh location au thed h the temper afus chang is being pac henpnatune n and whethe the te-panat is i”Chua s.ng.. olecneas.n a which the is ben Pancived 4. What would you expect to observe if KHCO, reacted with HBr? What test would you use to identify the product? 2. ame Violi ellow oz ine wate 5. How might a burning magnesium wire be used in a commercial application?Explanation / Answer
Basis for comparison
Physical change
Chemical change
Physical change refers to a change in which the molecules are rearranged but their internal composition remains same.
Chemical Change is a process in which the substance transforms into a new substance, having different chemical composition.
Example
ExampleTearing of paper, melting/freezing of water, cutting of trees, etc.
Burning of wood/trees/paper, rusting of iron, setting of curd, etc.
Nature
Reversible
Irreversible
Original matter
Original matter can be recovered
Original matter cannot be recovered
Involves
Change in physical properties of the substance, i.e. shape, size, color etc.
Change in chemical properties and composition of the substance.
Product Formation
No new product is formed.
New product is formed.
Energy
Absorption and evolution of energy do not take place.
Absorption and evolution of energy take place, during reaction.
In the above reaction effervescence is observed, this is due to release of CO2 gas. These gas can be detected by passing the same in to lime water then lime water turns in to milky white precipitate.
2Mg + O2 = 2MgO
Basis for comparison
Physical change
Chemical change
Physical change refers to a change in which the molecules are rearranged but their internal composition remains same.
Chemical Change is a process in which the substance transforms into a new substance, having different chemical composition.
Example
ExampleTearing of paper, melting/freezing of water, cutting of trees, etc.
Burning of wood/trees/paper, rusting of iron, setting of curd, etc.
Nature
Reversible
Irreversible
Original matter
Original matter can be recovered
Original matter cannot be recovered
Involves
Change in physical properties of the substance, i.e. shape, size, color etc.
Change in chemical properties and composition of the substance.
Product Formation
No new product is formed.
New product is formed.
Energy
Absorption and evolution of energy do not take place.
Absorption and evolution of energy take place, during reaction.
In the above reaction effervescence is observed, this is due to release of CO2 gas. These gas can be detected by passing the same in to lime water then lime water turns in to milky white precipitate.
2Mg + O2 = 2MgO
Basis for comparison
Physical change
Chemical change
Physical change refers to a change in which the molecules are rearranged but their internal composition remains same.
Chemical Change is a process in which the substance transforms into a new substance, having different chemical composition.
Example
ExampleTearing of paper, melting/freezing of water, cutting of trees, etc.
Burning of wood/trees/paper, rusting of iron, setting of curd, etc.
Nature
Reversible
Irreversible
Original matter
Original matter can be recovered
Original matter cannot be recovered
Involves
Change in physical properties of the substance, i.e. shape, size, color etc.
Change in chemical properties and composition of the substance.
Product Formation
No new product is formed.
New product is formed.
Energy
Absorption and evolution of energy do not take place.
Absorption and evolution of energy take place, during reaction.
Change in chemical properties and composition of the substance
Initial substances cannot be recovered
Absorption and evolution of energy take place, during reaction.
Sometimes light may be released
Small changes in temperature can be perceived by human. Small changes in temperature can be detected by thermo meters, thermo couples.
KHCO3 + HBr = KBr + H2O + CO2 (g)
In the above reaction effervescence is observed, this is due to release of CO2 gas. These gas can be detected by passing the same in to lime water then lime water turns in to milky white precipitate.
Burning Mg can be used commercially in crackers
2Mg + O2 = 2MgO
Basis for comparison
Physical change
Chemical change
Physical change refers to a change in which the molecules are rearranged but their internal composition remains same.
Chemical Change is a process in which the substance transforms into a new substance, having different chemical composition.
Example
ExampleTearing of paper, melting/freezing of water, cutting of trees, etc.
Burning of wood/trees/paper, rusting of iron, setting of curd, etc.
Nature
Reversible
Irreversible
Original matter
Original matter can be recovered
Original matter cannot be recovered
Involves
Change in physical properties of the substance, i.e. shape, size, color etc.
Change in chemical properties and composition of the substance.
Product Formation
No new product is formed.
New product is formed.
Energy
Absorption and evolution of energy do not take place.
Absorption and evolution of energy take place, during reaction.
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