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### Topic: Basic Phase change problem help  (Read 19494 times)

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#### mr cool

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##### Basic Phase change problem help
« on: January 30, 2009, 06:08:26 PM »
alright so im doing phase change problems and this is the question...  How many calories must be released to convert 100.0 grams of summer lake water at 65.0 C to winter ice at -10.0?

im really stuck on where to start then pretty much everything after that.  i hate phase change problems

also can someone tell me if my work on this problem is correct??

How many calories are required to convert 45.00 grams of liquid water at 30.0*C to steam at 110.0*C?

(80cal/g)(45.00g)+(80cal/g*C)(30.0*C)+(45.00g)(540cal/g) and i got 30300 calories.

ps.. the * is my makeshift degrees symbol for now.

thanks

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #1 on: January 30, 2009, 07:00:13 PM »

#### mr cool

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##### Re: Basic Phase change problem help
« Reply #2 on: January 30, 2009, 08:20:39 PM »

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #3 on: January 30, 2009, 08:32:01 PM »

#### mr cool

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##### Re: Basic Phase change problem help
« Reply #4 on: January 30, 2009, 08:56:20 PM »
Would it be (.5cal/g)(100.0g)(65.0 C -10.0 C)?  It came out too 3240

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #5 on: January 30, 2009, 09:04:17 PM »

#### mr cool

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##### Re: Basic Phase change problem help
« Reply #6 on: January 30, 2009, 09:12:44 PM »
Would i use heat of formation to do this? Such as 80 cal/g?  If so do i have to make it like -80 cal/g or something?

Does this work?.

(80.0 cal/g)(100.0g) = 8000 cal.?

This is for b.) by the way

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #7 on: January 30, 2009, 09:16:17 PM »

Dear reezyfbaby;

Bravo! -  Correct!
Now whats the final value for c.)?

Good Luck!
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#### mr cool

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##### Re: Basic Phase change problem help
« Reply #8 on: January 30, 2009, 09:17:42 PM »
I wound up with 17740 calories...

Thanks for the help man.

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #9 on: January 30, 2009, 09:22:22 PM »

#### mr cool

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##### Re: Basic Phase change problem help
« Reply #10 on: January 30, 2009, 09:28:12 PM »
Ok now i got ya... It is a lot easier if you just take it step by step. I got 15000 cal

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #11 on: January 30, 2009, 09:31:13 PM »

#### mr cool

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##### Re: Basic Phase change problem help
« Reply #12 on: January 30, 2009, 09:52:22 PM »
Oki doki, here is a shot at my other problem,
A.)---(1.0 cal/g)(45.00)(100*C - 30*C)=3150 I did 100 - 30 to get up too 100*C
B.)---(540 cal/g)(45.00) = 24300  im not sure if i did B.) correct
C.)---(.5 cal/g)(45.00)(0+10) = 225
Total.)--- 27675 calories.

Im not positive but i think i did alrght other than step number 2.

Anyone feel like seeing if i did it correct? Thanks.

#### ARGOS++

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##### Re: Basic Phase change problem help
« Reply #13 on: January 30, 2009, 09:55:52 PM »

Dear reezyfbaby;

Congratulation!,   -  Exact result!

Good Luck!
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#### mr cool

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##### Re: Basic Phase change problem help
« Reply #14 on: January 30, 2009, 09:59:54 PM »
Thanks for the help man, i'm going to hit the hay and maybe put up some more tries at my problems tomorrow. Thanks again