Which of these are physical changes? Which are the chemical changes and why?

1.Wet clothes are dried out by the sun. (Physics, belongs to the phenomenon of evaporation) 2Copper is produced in moist air to form green copper. (Chemical, oxidation reaction with oxygen and water in the air).

3.Paper burns. (Chemical, paper and oxygen combustion).

4.The porcelain bowl is broken. (Physics).

5.Iron rusts. (Chemical, oxidation reaction with water and oxygen in the air) 6Paraffin melts. (Physical, solid to liquid).

7.Breathe in front of a glass window in the cold winter, and a layer of water mist appears on the glass. (Physics, liquefaction phenomenon).

8.Put a ball of snow in a warm room on a snowy day and the snow melts. (Physical, solid to liquid).

1 Physical changes.

2 Chemical changes.

3 Chemical changes.

4 Physical changes.

5 Chemical changes.

6-8 are all physical changes.

The most basic way to tell the difference between physical change and chemical change is to see if there's any new substance being formed, for example, the most likely thing to go wrong in your question: the burning of paper, which reacts with oxygen in the air at high temperatures to form carbon black and other new oxides that weren't available before

For example, the last one is ice that turns into water, it's all water, but the state changes from solid to liquid, and the matter itself doesn't change, and no new matter is produced, so it's a physical change.

This kind of problem is very simple: read more books, pay attention to associations, pay attention to observation, and it is not difficult to good luck

1. 4。 6 。7 8 is a physical change.

Others are chemical changes.

Physical change does not produce new matter, only a change in the physical state.

Chemical changes definitely lead to the creation of new substances.

Absolutely correct I am the Department of Physics, Peking University.

1 thing. 2.

3. 4 things.

5. 6 things.

7 things. 8 things.

The formation of a new substance is a chemical change.

It's a physical change, it's a chemical change.

The biggest difference between physical change and chemical change is whether the molecule has been redivided, taking the change of water as an example, the mutual transformation of the three states of water, ice and water vapor is a physical change, the water molecule is still a water molecule, and the water molecule is not redivided, so their mutual transformation is a physical change, and the electrolysis of water to produce hydrogen and oxygen is a chemical change, because the covalent bond between hydrogen and oxygen in the water molecule is broken, and after the water molecule is redivided, the obtained atoms are recombined into oxygen and hydrogen. So the electrolysis of water to produce hydrogen and oxygen is a chemical change. Do na.

Here please note Kaihu Zen, the mutual transformation between the elements is not all physical changes, for example, white phosphorus isolates the air and stares at the dust and heats up into red phosphorus, under normal circumstances, white phosphorus and red phosphorus are only represented by a P, but in fact, the chemical formula of white phosphorus is P4, and red phosphorus is a giant covalent molecule, amorphous, in the process of transformation from white phosphorus to red phosphorus, the redivision of white phosphorus molecules (phosphorus-phosphorus bond breakage) occurs, and then recombination into red phosphorus, so the conversion of white phosphorus to red phosphorus is actually a chemical change.