Question

WILL REWARD MEDAL/FAN!!!((:
A blacksmith heat an iron bar to 1445 Celsius. The blacksmith then tempered the metal by dropping into 42,800 cm^3 of water that had a temperature of 22Celsius. The final temperature of the system was 45 Celsius. What was the mass of the bar?

Answer 1

so the temperature of the water has risen by \(45-22 = 23^{\circ}C\)

Answer 2

that's the delta t right?

Answer 3

Yes, then the heat added to the water is given by,
\(Q=c*m*\Delta t=4.18*42800*23 = 4114792 J\)

Answer 4

That means the bar has lost the same amount of heat.

You can use that to find the mass of bar

Answer 5

Oh I see.

Answer 6

so basically it will be 4114792 = mass x 0.446 x (1445-45) Celsius
which gives you the mass is 65890 grams or 6.6 kilograms?

Answer 7

0.446 is specific heat of iron is it ?

Answer 8

yeah

Answer 9

Looks good !

Answer 10

thanks can you also help me with this one?

Answer 11

a 752 cm^3 sample of water was placed in a 1 kg aluminum pan. The initial temperature of the pan was 26 Celsius, and the final temperature of the system was 39 Celsius. What was the initial temperature of the water?

Answer 12

looks like a similar problem..
give it a try

Answer 13

well i got stuck because i wasn't sure
0.902 j/ 1gC x (39- delta t) x 1000g = 752 cm^3
totally got that wrong i'm guessing

Answer 14

First, write down the given info
Water :
\(m = 752 cm^3 = 752 g\)
\(c = 4.18 J/G^{\circ}C\)
\(\Delta t = ?\)

Aluminium pan :
\(m = 1kg= 1000 g\)
\(c = 0.9 J/G^{\circ}C\)
\(\Delta t = 13\)

Answer 15

how do we know what the delta t is if we don't have the q of the equation ( i think that is the energy released)?

Answer 16

Energy released by water = Energy absorbed by aluminium pan

Answer 17

\[4.18*752*\Delta t = 0.9*1000*13 \]

you can solve \(\Delta t\)

Answer 18

oh okay
and would that be 39-26?

Answer 19

wait hold on

Answer 20

oh never mind so now you just basically solve for the delta t right
and the answer would be in celsius?

Answer 21

what do you get for \(\Delta t\) ?

Answer 22

3.72 Celsius...

Answer 23

good
\(\Delta t = 3.72 \)
and you know that final temperature = \(39\)

so initial temperature = ?

Answer 24

so subtract?

Answer 25

careful, water has lost some heat
that means the initial temperature is greater than the final temperature

Answer 26

oh oops i read it wrong
i mean add
because the final temperature was the result of the two temperatures
i accidentally interpreted it wrong
42.72 Celsius?

Answer 27

Yep, 42.72 C looks good

Answer 28

The fuel value of peanuts is 25 kj/ gram. If an average adult needs 2800 kilocalories of energy a day, what mass of peanuts would meet an average adult's energy needs for the day? Assume all of the fuel value of the peanuts can be converted to useful energy.

Answer 29

I am confused about what calories are.

Answer 30

dont get confused, all the problems you have been working on are similar...

if we don't know what calorie means, we can always google :)

Answer 31

the main reason i suck at these problems is that my teacher just gives it to me along with the specific heat formula, so I don't get almost everything

Answer 32

Yes, that is all we ever need to work these problems

First things first, lets put down the given info

Answer 33

25 kj/ grams
2800 kilocalories of energy a day
we are finding mass

Answer 34

google gave me

1 kilocalorie =
4184 joules

Answer 35

yeah i think a calorie is like 4.18 something per joules.

Answer 36

right, so 2800 kilocalories = how many kilojoules ?