Question

q=mcAT question:

If 0.4kj of heat is removed from a sample of water and it cools from 25 degrees Celsius to 15 degrees Celsius, what is the mass of the water?

I keep getting 0.01, but I know the answer is 10 - help?

Answer 1

the answer depends on the units.. its 0.01kg or 10g..

Answer 2

both kg and g are units of mass, what value you end up with will depend on the units of your c and then you can convert to whatever you want

Answer 3

We haven't gotten up to kg yet, it's still the first lesson, so I assume were sticking to g.

Answer 4

Main point is: Do you know where I went wrong?

Answer 5

I'm happy to provide work.

Answer 6

you didn't go wrong... you have to always include the units when you are solving problems.. do you know what the units are for the value of 4 that you posted?

Answer 7

g

Answer 8

It was actually 4.18, but we had to round to the nearest sig fig.

Answer 9

the value of c ~ 4 kJ / (kg * C)

Answer 10

But isn't that the formula for raising heat 1 degree higher? Shouldn't I use the mcAT form.?

Answer 11

*confused

Answer 12

yes you will use the q = mcat equation... can you rearrange that formula to determine the mass?

m = what?

Answer 13

m= q/cAT ?

Answer 14

yes that's correct.. now fill in the variables while including the units.. which is what you did before as well

Answer 15

(0.4 kJ)/ (4 kJ/ (kg * degree c) * 10 degrees C)

Answer 16

so just note that whatever you get.. the answer will be in kilograms... and there are 1000 grams in 1 kilogram.. so you can convert to get the answer in grams

Answer 17

are you sure that makes sense?

Answer 18

Yup, my work was all over the place. Plus I didn't change the formula for mass like you did - I'll be sure to use that next time.