Using specific heat stuff to find amount of heat(Q=mCT)

In summary, the quantities of energy required for the given changes are ranked as follows: raising the temperature of 2 kg of H2O from -1°C to 2°C (e) requires the most energy, followed by (a), (b), (c), and finally (d) requires the least amount of energy. The ranking is e > a = b = c > d. This is due to the additional energy required for melting ice in (e).
  • #1
Raziel2701
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Homework Statement


Beryllium has roughly one-half the specific heat of liquid water (H2O). Rank the quantities of energy input required to produce the following changes from the largest to the smallest. In your ranking, note any cases of equality. (Use only the symbols > or =, for example a>b=c)

(a) raising the temperature of 1 kg of H2O from 20°C to 26°C
(b) raising the temperature of 2 kg of H2O from 20°C to 23°C
(c) raising the temperature of 2 kg of H2O from 1°C to 4°C
(d) raising the temperature of 2 kg of beryllium from -1°C to 2°C
(e) raising the temperature of 2 kg of H2O from -1°C to 2°C

Homework Equations



[tex]Q=mC\Delta T[/tex]

The Attempt at a Solution



For (a) I get 25116 J
For (b) I get 25116 J
For (c) I get 25116 J
For (d) I get 12558 J
For (e) I get 25116 J

So the answer I put in is a=b=c=e>d but it tells me it's incorrect. I found these answers simply by subtracting the final temperature from the initial, multiplying it by the mass and multiplying by the specific heat of water where relevant. For d I used 2093 as my specific heat, and for the rest I used 4186.

No clue what is wrong.
 
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  • #2
(e) tricky, to go from water at -1 to 2, you have to heat ice from -1C to 0C and then melt it and then heat water from 0C-2C

Even without knowing the numeric value for the melting energy of ice you know that it takes energy
 
  • #3
Ah that's what I missed. Yeah that would make "e" the one to take the most energy since there would be a latent heat of fusion calculation in there.

Thanks!
 

1. What is specific heat and how is it used to find the amount of heat?

Specific heat is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. It is used in the equation Q=mCT to calculate the amount of heat (Q) released or absorbed by a substance, where m is the mass of the substance, C is the specific heat, and T is the change in temperature.

2. How do you determine the specific heat of a substance?

The specific heat of a substance can be determined experimentally by measuring the amount of heat added or removed from a known mass of the substance and the change in temperature. The specific heat can then be calculated using the equation C=Q/mT.

3. Can specific heat be negative?

No, specific heat cannot be negative. It is a physical property of a substance that is always positive. A negative result in the Q=mCT equation indicates a decrease in temperature, which means that heat is being released from the substance.

4. Why is it important to use specific heat to find the amount of heat?

Using specific heat to find the amount of heat is important because it allows scientists to accurately measure the energy transferred during a chemical or physical process. This information is crucial in understanding the behavior of substances and their interactions with one another.

5. Are there any limitations to using specific heat to find the amount of heat?

Yes, there are a few limitations to using specific heat to find the amount of heat. This method assumes that the specific heat of a substance remains constant over a given temperature range, which may not always be the case. Additionally, it does not take into account any energy lost to the surroundings during the process, which can affect the accuracy of the calculated value.

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