Calculating joules?

Question

i know joules is the measure of work but i am not sure how to calculate it,my teacher just wont help me ,please tell me each step to calculate these plz dont give me just the answer, i wanna learn how to do it.


when 25.0 grams of water are cooled from 20.0 cellcius to 10.0 celsius the number of joules of heat energy released is
a 42 b 105 c 840 d1050

how many kilojoules of heat energy are absorbed when 100.g of water are heated from 20.0c to 30.0 c by the addition of 3762 j. what is the mass of water? a0.03g b 30.0g
c 0.30 g d 300.0

Answer 1

The heat capacity of water is 1 cal per g per degC or 4.184 J per g per degC.

20.0C - 10.0C = 10degC

25gH2O x 10degC x 4.184J/cal-degC = 1046J, or 1050J to two significant figures. d. is correct

The next question is confusing, because it asks for kJ but says 3762J are added. It asks for the mass of water, but says 100g H2O.

Answer 2

Hi Rooney,
I imagine you dont study at University ok? Because many things can be forgot if you dont. Ex:
Is there thermic cover? What is the temperature of air around? Is there Wind?

These are especific heat problems and you can solve them by expression: Q=m*c*delta T , where:

Q is exchanged heat in calories
m is mass in grams
c is specific heat in cal/g. C
delta T is difference between Tf and Tb ; (Tf-Tb)=>>Tf=final temperature and Tb is temperature of begin
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1st. The goal is to discover what is the Q.
Q=?
Data:
m=25g of H2O c=1cal/g.C (to water) delta T=Tf-Tb ==> T=10-20= -10 C (take care the signal)
So,
Q=25.1.(-10)=-250
[Q]= g*cal/g.C*C=cal Q=-250 cal ( minus signal= lost heat)

But you want the answer in Joules, not in calories (another unit heat), so we need to convert it:
1 cal = 4.19 Joules
-250 cal = x

x = -1047,5 J

Rounding the answer, we have -1050 J. The difference was caused because in your book 1cal= 4.2J. No problem! Use 4.2J.
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2nd. I didnt understood the idea of your text. I dont know speak english very well, but i think may be you did wrong copy.

Goal is mass (m), but mass is 100g (!?)

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another possible solution, if you want to know the mass

Q=m*c*delta T
goal, m=?
Remember first grade equations?

m*c*delta T=Q
m= Q / (c*deltaT),

and this is the expression for to calculate mass. You can do the same thing if want to know the others variables. Such as, you can have 4 different expressions from this expression, because there are 4 variables!

I hope have helped.
#################
PS. Joule IS THE UNIT OF HEAT, WORK OR ENERGY!!!
anothers units are cal and BTU.

Answer 3

Joules are a measure of energy, not work.

I takes 4.186 joules to change the temperature of 1 gram water by 1 degree, except for temperatures of freezing and boiling. (Assuming standard pressure).

So for 25 grams, it takes
4.186 x 25 x 10 joules to go from 20 C to 10 C
= 1046.5 J, or about 1050 J

Answer 4

what is the mass of water?
1 cc of water is 1 gram
1 fluid once of water is 1 oz
1 gallon = 8lbs =128 oz
1L of water is 2.2 lbs= 1 Kg or 1000 grams.
what planet are you from?

Answer 5

1...1,050 J (Actually 1,046J).
2...Your question is totally incorrect...
Ignoring your 100g of water in this question...
3,762J = ?g x 10 x 4.184 = 41.84 x ?g
?g = 3,762/41.84 = 89.9grams of water.