Posted by Connie on Saturday, September 10, 2011 at 10:36am.
What is the amount of energy of calories to heat 8.5g of water from 15 C to 36 C?
I think you take 8.5g x 21 degree C, but then I am stuck. Thank you
Chem - Jai, Saturday, September 10, 2011 at 10:50am
amount of energy absorbed or released is given by
Q = mc*(T2 - T1)
where
Q = heat (in Joules)
m = mass (in grams)
c = specific heat capacity (J/g-K)
T = temperature (in Celsius or Kelvin)
*note that Q is (+) if the object absorbed heat, and (-) if it released heat.
for water, c = 4.184 J/g-K (you can find this in books or you can google this)
substituting,
Q = 8.5*4.184*(36-15)
Q = ?
now solve for Q. units in Joules.
hope this helps~ :)
First, thank you, I get 746.844J but my book says the answer is 180 cal---what am I not doing correctly?
To convert the answer from Joules to calories, you can use the conversion factor that 1 calorie is equal to 4.184 Joules.
So, to convert 746.844 Joules to calories:
746.844 Joules * (1 calorie / 4.184 Joules) = 178.95 calories
Rounding to the nearest whole number, the answer is approximately 179 calories. It seems that there might be a rounding or conversion error in your book.
To convert the answer from Joules to calories, you need to know the conversion factor between the two units. One calorie is equivalent to 4.184 Joules.
To convert 746.844 Joules to calories, you can use the conversion factor:
180 cal = 1 cal
4.184 J x J
So, to convert 746.844 Joules to calories, you can multiply by the conversion factor:
746.844 J x (1 cal / 4.184 J) = 178.42 cal (rounded to two decimal places)
Therefore, the answer in calories is 178.42 cal, which is close to the value given in your book (180 cal). It's possible that there may be slight differences due to rounding or different conversion factors used.