chemical and physical changes. please help im so confused

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[erinoglesby]

hi! ok so i am sooo lost on my homework and i have a huge test tomorrow! if there is anyone who can help that would be great! and i can help u back! ok so the question im stuck on is -what is the summary of observed behavior? and then the other question im lost on is what is the physical or chemical change?
please please help

[Otis]

A physical change is a change of the substance without changing it chemically, it's still the same substance. A few examples, water (H2O) will undergo change of state when frozen (solid - ice)) or boiled (gas - steam) but it remains H2O. Sugar will dissolve in water but when the water is evaporated the sugar remains. A piece of copper can ground into fine dust or be pounded into a flat sheet then cut with shears into tiny pieces. These small pieces can be melted and formed into a single piece again. There was no change of the substance during any of these processes.

In a chemical change you end up with something different - It has gone through a chemical reaction. Water reaction with nitrogen dioxide (NO2) in the atmosphere to form nitric acid (HNO3) a constituent of acid rain. Hot sodium (Na)reacting with chlorine gas (Cl2) to form sodium chloride (NaCl). Wood burning, wine fermenting, iron rusting are examples of a chemical change - the products are different from the starting materials.

Hope this helps,

Otis

[erinoglesby]

omg! thank u so much that makes so much mre since! i have another question if thats ok...um ok what is the summary of observed behavior?

[Otis]

If this is from a post lab then it's a summary of *your* observations during the lab.

Otherwise, the question has no context for me to be helpful.

Best of luck,

Otis

[erinoglesby]

ok thanks again! thats where i got stuck is we havent done any labs lately