Question

1. classify each description as a physical change or chemical change.

a) milk spoiling in the fridge and starting to sour
b) transforming iron into steel using a blast furnace
c) water evaporating from a sidewalk in a hot day
d) dissolving sugar into coffee
e) digesting food after eating a large meal
e) popping popcorn in a microwave
f) shredding paper
g) a firework exploding

Explanation:

• a) Milk spoiling is a chemical change as new substances are formed by bacterial action.
• b) Transforming iron to steel is a chemical change as the composition changes through reactions in the blast - furnace.
• c) Water evaporating is a physical change as it is a change of state from liquid to gas without changing the substance's chemical identity.
• d) Dissolving sugar in coffee is a physical change as it is a mixture formation without new chemical substances.
• e) Digesting food is a chemical change as enzymes break down food into new substances.
• f) Popping popcorn is a chemical change as heat causes chemical reactions in the kernels.
• g) Shredding paper is a physical change as it only changes the physical form, not the chemical composition.
• h) A firework exploding is a chemical change as it involves rapid chemical reactions producing heat, light, and new substances.

Answer:

a) Chemical change
b) Chemical change
c) Physical change
d) Physical change
e) Chemical change
f) Chemical change
g) Physical change
h) Chemical change