Homework Help: To: Bobpursely

Posted by Sara on Wednesday, April 7, 2010 at 7:46pm.

You helped me with my observations yesterday, but I need help with my questions as well. I tried to answer as many as I could by myself, but I'm having difficulties understanding some. Pointing me towards the right direction would be helpful, thanks.

Questions:

Which changes that u noted in step 4 were physical? which were chemical?

I wrote: Changes in step 4 which were physical were the candle melting and the flame growing. Changes in step 4 which were chemical were the oxygen and the wick burning.

I am kind of having troubles identifying which changes are chemical and which are physical so I'm not sure which other occured changes were physical and which were chemical.

What evidence showed the release of energy? what forms of energy were produced by the burning candle? where was this energy in the unlit candle?

I wrote:
The flame growing hotter and hotter; heat is given off. This energy was in the wick --Please correct me if I'm wrong, thanks

based upon your analysis of your observations in Part 3, what are 2 substances produced by the combustion of the candle?

-I dont get this question-- i dont know the answer. i'll guess and say that bubbles were produced.

How does the mass of the candle change during combustion, explain this change in mass.?????????????????

Is it because of the wax starting to melt?

is there any evidence that the candle needs something from the air to help it burn? what might this something be?

- I dont get the first part but is the second one oxygen and hydrocarbon?

To: Bobpursely - bobpursley, Wednesday, April 7, 2010 at 7:56pm
You did not read my response.

Physical changes: wax melted, then wax vaporized.

CHemical change: wax vapor and oxygen in air changes to combustion products. THe cobalt paper tested for water vapor in the "fumes", and the limewater tested for carbon dioxide. So the output of the combustion was water and carbon dioxide.

The mass of the candle changes because it is consumed in the burning. As for a evidence that something in the air was contributing to the burning, didn't the candle smother, or at least reduce the burn rate, when you put the coil down over it to shut off the air?
To: Bobpursely - Ms. Sue, Wednesday, April 7, 2010 at 8:03pm
Sara -- if you expect us to help you, you must thoroughly read all responses. It's discouraging for us to post an answer -- only to find that the student has ignored it.
To: Bobpursely - Sara, Wednesday, April 7, 2010 at 8:07pm
sorry Ms. Sue, sorry bobpursley for that inconvenience.

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