Physical or Chemical change?

Question

can you let me know which of the following is primarily a physical or primarily a chemical change:

1) boiling an egg
2) freezing ice cream
3) souring milk
4) boiling water
5) formation of a snowflake
6) churning cream to make butter

Answer 1

1 chemical
2physical
3chemical
4physical
5physical
6physical

Answer 2

1) boiling an egg is actually a complicated matter. For the most part, the change in the egg's properties is caused by denaturation of proteins, which is a physical change. However, there are also likely to be disruption/formation of disulfide bonds and possibly amide crosslinks between amines and acids, which would fall into the category of chemical change. Either answer is justifiable.

2) freezing ice cream is a physical process. It's not any different than freezing water.

3) souring milk is a chemical change. I'm not sure if it's from acellular oxidation of, for example, the milk fat, or if it's from anaerobic metabolism by bacteria. Either way, there are chemical reactions going on.

4) boiling water is a physical change. The water molecules are the same whether they are in liquid form or gaseous form.

5) formation of a snowflake is a physical change. Again, the water molecules are the same whether they are in the air, or in a crystalline lattice.

6) as far as I know, churning cream into butter is only a physical process. Cream is a fat emulsion. When you churn it, you are de-emulsifying it by disrupting the fat globules. There are no chemical reactions taking place.

Answer 3

1. Chemical Change
2. Chemical Change
3. Chemical Change
4. No Change
5. Physical Change
6. Chemical Change