Physics question for you smarties

[Wolfala]

Lets see how smart our O-Club is late at night - b/c i'm tired and my feet are cold.

Find the total energy at 1 atmosphere of pressure required to heat one mole of ice from -100 deg Celsius to ultimately form water vapor at + 200 deg Celsius.

This is a 5 step process:
 

   1. Heating ice from -100 deg to 0 deg, using the heat capacity of solid water (ice)
   2. Melting the ice to form water at 0 degrees, using the heat of fusion (also called enthalpy of melting)
   3. Heating liquid water from 0 degrees to 100 degrees, using the heat capacity of liquid water
   4. Evaporating liquid water to form water vapor (steam), using the heat of vaporization (also called enthalpy of vaporization)
   5. Heating steam from 100 degrees to 200 degrees, using the heat capacity of water vapor (the gaseous phase of water)

 
As a partial check on your calculations, do a dimensional analysis on the units. Each of the 5 terms in the sum (and the answer) should have units of J (joules)….

Good luck!

S!

Wolf

[B@tfinkV]

1 X kettle with 240V mains power.

1 X pint mug

1 X spoon of suger

2 X heaped spoons instant coffee

a dash of milk

[Redwing]

61221.6 J
or 61.2216 kJ
or 14621.83 calories

dT = Q / cp is the only formula you need


How about this one:
A hot air ballon has a volume of 2500 cubic meters and a takeoff weight (mass) of 250 kg. Outside temperature is 15 degrees C.
At what inside temperature will it take off?

Assume air is an ideal gas with a volume of 22,4 liters per mole and consists of 20% oxygen (O2) and 80% nitrogen (N2).

[AWMac]

Originally posted by B@tfinkV
1 X kettle with 240V mains power.

1 X pint mug

1 X spoon of suger

2 X heaped spoons instant coffee

a dash of milk

Haaaaaaa...... you forgot:

2 X Shots of Baileys.

[DREDIOCK]

Do your own homework


Now here's one for you guys.


Without looking it up in the dictionary

How many know what the word "congruent" means?

And if you do. Would you use it in a homework assignment for a 9 year old?

[lasersailor184]

I would if they are learning about geometry...  But then again I wouldn't have just thrown the word out there.  I would have explained what it is first.



PS. I hate thermodynamics with a passion.

[john9001]

the answer is 300 kelvanators.

[Holden McGroin]

Actually the easiest way is to look it up in steam tables.

But from memory, and in English units

960 or so btu / lb latent heat of evap

80 or so  btu / lb latent heat of liquid/solid

960 + 80 + 180*in ice form, + 180* in steam form should get you in the ball park. (1400 btu / lb)

*a guess for hc solid and hc v, I would have to look that up in Marks before I put a stamp to it.

[Mustaine]

no

the answer is 1.21 jigawatts

[Sandman]

Bah... too easy.

Tell us why ice is slippery.

[Mustaine]

Originally posted by Sandman
Bah... too easy.

Tell us why ice is slippery.

because it doesn't like you and wants to make you fall sandy.

[Reschke]

To many steps just get a pan and put the ice cube in it on the cook top. Turn cooktop eye to HIGH and watch.

[mietla]

Originally posted by Sandman
Bah... too easy.

Tell us why ice is slippery.

It's not ice. It is a thin layer of water. The pressure you exert on ice changes the melting point and causes it to melt on contact.

Take a block of ice and place the ends of it on two chairs, so the the block is suspended in the air (like the brick or a cement block for the karate chop). Now take a wire with weights on both ends. Place it over the block such that each weight is on the opposite side of the block. You'll see that with time the wire will cut through the ice and fall down below, but the ice block will remain in one piece.

The pressure the wire exerts, melts the ice beneath the wire causing it to slowly cut through, but the water immediatelly freezes above the wire (no pressure there), so the block remains intact after the experiment.

[crowMAW]

Originally posted by Wolfala
Find the total energy at 1 atmosphere of pressure required to heat one mole of ice from -100 deg Celsius to ultimately form water vapor at + 200 deg Celsius.  

I never liked iced mole...the wiskers tickle once they thaw.

[nirvana]

Congruent for a 9 year old, no.  Go have a talk with the teacher.


Ice melts due to a thin layer of water, like previously stated.