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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: helpmeimnoob on January 01, 2008, 11:16:37 PM

Title: a basic phase change problem
Post by: helpmeimnoob on January 01, 2008, 11:16:37 PM

Ok, its winter break and I totally forgot how to do chemistry problems from last year so can you remind me how to do this problem?

How many joules does it take to heat 50.0 grams of water at 0.0 degrees celceus to 50.0 degrees celceus?

Title: Re: a basic phase change problem
Post by: Alpha-Omega on January 01, 2008, 11:31:58 PM

OK you have 50.0 g H2O
To = 0.00 C
Tf = 50.0 C
What is the specific heat of water?  (get it from a table in your text book)
Heat(cal)= Mass(g) x T change in degrees C x specific heat (cal/g x degree c).

You will have to convert your calories to Joules.  That iis also in a table in your text book.

GOOD LUCK!!!!!!!!!!!!!!!!!!!!!!

Title: Re: a basic phase change problem
Post by: helpmeimnoob on January 01, 2008, 11:38:33 PM

ok, wait cant i just do like..

specific heat of water (J/g x c) x 50g x 50 degrees c ?

Title: Re: a basic phase change problem
Post by: Alpha-Omega on January 01, 2008, 11:49:03 PM

You sure can....since:

The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance.

BTW- there is a site on the web....that will allow you calculate these just by plugging in the variables.....check your answer here:

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html