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. evolutio너 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?

Answer 1

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.

1. Change in chemical properties and composition of the substance
2. Initial substances cannot be recovered
3. Absorption and evolution of energy take place, during reaction.
4. Sometimes light may be released

1. Small changes in temperature can be perceived by human. Small changes in temperature can be detected by thermo meters, thermo couples.
2. KHCO₃ + HBr = KBr + H₂O + CO_{2 (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.

1. 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.

1. Change in chemical properties and composition of the substance
2. Initial substances cannot be recovered
3. Absorption and evolution of energy take place, during reaction.
4. Sometimes light may be released

1. Small changes in temperature can be perceived by human. Small changes in temperature can be detected by thermo meters, thermo couples.
2. KHCO₃ + HBr = KBr + H₂O + CO_{2 (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.

1. 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.

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