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Topic: Energy and Changes of State  (Read 3189 times)

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Offline quest10

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Energy and Changes of State
« on: July 26, 2009, 08:06:01 PM »
Hello,  I have attempted this question and was hoping to have some help.

This is the question:

Purpose: To plot the change of temperature due to the absorption of energy for a chemical as it changes phase from solid to liquid to gas.

Create a plot of temperature versus added energy in joules for a 1.0 g sample of ethanol over a temperature range of   -180oC to 180oC. The relevant values for your calculations are:

sp. heat (solid) = 0.54 J/g.oC         melting point = -114oC        heat of vaporization = 854 J/g
sp. heat (liquid) = 2.44 J/g.oC        boiling point = 78oC
sp. heat (gas) = 0.81 J/g.oC
heat of fusion = 104 J/g

1.   Calculate the following amounts of energy:

(a)   Joules to heat 1.0 g of solid ethanol from -180oC to -114oC
(b)   Joules to melt 1.0 g of solid ethanol
(c)   Joules to heat 1.0 g of liquid ethanol from-114oC to 78oC
(d)   Joules to boil 1.0 g of liquid ethanol
(e)   Joules to heat 1.0 g of gaseous ethanol from 78oC to 180oC

2.    On graph paper, scale the x-axis in joules from 0 to 1600 (this should be the approximate total energy required). Scale the y-axis from -180 to 180

3.   Make your plot with 5 distinct straight lines:

•   Line 1: Joules increase by the amount in 1 (a); temperature increases from -180oC to -114oC.
•   Line 2: Joules increase by the amount in 1 (b); no temperature increase (a straight line).
•   Line 3: Joules increase by the amount in 1 (c); temperature increases from -114oC to 78oC
•   Line 4: Joules increase by the amount in 1 (d); no temperature increase.
•   Line 5: Joules increase by the amount in 1 (e); temperature increases from 78oC to 180oc.

****************************************************************************************

Ok so this is what I tried. Should I keep all of the answers in KJ or is it ok to convert it to scientific notation? and if so, is it now in J?:

1. a)

1.0g x (-180 -(-114oC)) x 0.54 J/g.oC x 1KJ/103J
1.0g x (-66oC) x 0.54 J/g.oC x 1KJ/103J

0.03564 KJ  :rarrow: 3.56 x 10-2J
Did I do everything correct with the degrees?  is it just -114? or -66?

1. b)

1.0g x 104 J/g. x 1KJ/103J
= 0.104 KJ or 1.04 x 10-1


1. c)

1.0g x (-114 -(78oC)) x 2.44 J/g.oC x 1KJ/103J
1.0g x (-36oC) x 2.44 J/g.oC x 1KJ/103J

Again did I do everything correct with the degrees?  is it just 78? or do i subtract 78 from -114? i didn't do the answer because I'm unsure of the degrees

1. d)

1.0g x (78oC)) x 2.44 J/g.oC x 1KJ/103J
= .190KJ or 1.90 x 10-1


1. e)

Is this supposed be mass x heat of vaporization = heat or is it mass x  :delta:t x sp.heat (gas) = heat?  I completed the following in heat of vaporization

1.0g x (854 J/g x 1KJ/103J
= .854 KJ  :rarrow: 8.54 x 10-1J

For Part 3 do i just take the answers from part 1 and plot them on graph paper or are there other calculations I should do?  For some reason the wording is not clear to me.

Thanks again for the help  ;D

Offline Astrokel

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Re: Energy and Changes of State
« Reply #1 on: July 26, 2009, 10:36:29 PM »
Quote
Should I keep all of the answers in KJ or is it ok to convert it to scientific notation? and if so, is it now in J?
I'm fine with any of it as long as you got the answer right.

Quote
Did I do everything correct with the degrees?  is it just -114? or -66?
:delta: T = Tfinal - Tinitial

Quote
Is this supposed be mass x heat of vaporization = heat or is it mass x  :delta:t x sp.heat (gas) = heat?  I completed the following in heat of vaporization

There should be no increase in temperature during change of state.
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

Offline quest10

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Re: Energy and Changes of State
« Reply #2 on: July 27, 2009, 05:45:29 PM »
Thanks so much for your *delete me*

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