What did I do wrong on these specific heat problems?

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username5575986
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#1
Report Thread starter 8 months ago
#1
I had to answer these questions that have to do with finding specific heat, mass, heat energy, and change in temperature and I tried to do them but I got them wrong for some reason. Can someone explain to me what I did wrong?

1. Determine the mass of a sample of silver if 705J of heat are required to raise its temperature from 25oC to 36oC. The specific heat of silver is 0.235J/goC.
Answer: 273

2. If 31,500J of heat is used to warm 750g of water, what is the temperature change? The specific heat of water is 4.184J/goC.
Answer: 10.0

3. If the specific heat of iron is 0.46J/goC, how much heat is needed to warm 50.0g of iron from 20.0oC to 100.0oC?
Answer: 1840

4. If it takes 105J to warm 100.0g of aluminum from 10.0oC to 25.0oC, what is the specific heat of aluminum?
Answer: 0.070
Last edited by username5575986; 8 months ago
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charco
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#2
Report 8 months ago
#2
(Original post by AntiAW)
I had to answer these questions that have to do with finding specific heat, mass, heat energy, and change in temperature and I tried to do them but I got them wrong for some reason. Can someone explain to me what I did wrong?

1. Determine the mass of a sample of silver if 705J of heat are required to raise its temperature from 25oC to 36oC. The specific heat of silver is 0.235J/goC.
Answer: 273

2. If 31,500J of heat is used to warm 750g of water, what is the temperature change? The specific heat of water is 4.184J/goC.
Answer: 10.0

3. If the specific heat of iron is 0.46J/goC, how much heat is needed to warm 50.0g of iron from 20.0oC to 100.0oC?
Answer: 1840

4. If it takes 105J to warm 100.0g of aluminum from 10.0oC to 25.0oC, what is the specific heat of aluminum?
Answer: 0.070
All of these questions use the same equation:

Energy = mass x specific heat capacity x temperature change

So question 1

Determine the mass of a sample of silver if 705J of heat are required to raise its temperature from 25oC to 36oC. The specific heat of silver is 0.235J/goC.

You have to make "mass" the subject of the equation:

mass = Energy/(specific heat capacity x temperature change)

and substitute values.

mass = 705/(0.235 x 11) = 273g
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username5575986
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#3
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#3
(Original post by charco)
All of these questions use the same equation:

Energy = mass x specific heat capacity x temperature change

So question 1

Determine the mass of a sample of silver if 705J of heat are required to raise its temperature from 25oC to 36oC. The specific heat of silver is 0.235J/goC.

You have to make "mass" the subject of the equation:

mass = Energy/(specific heat capacity x temperature change)

and substitute values.

mass = 705/(0.235 x 11) = 273g
Yeah, but the other questions have different equations.

For question #2, it's asking me for temperature change. So, I did (31,500 J) / (750g) x (4.184J/gC) and got 10.0. (Rounded to sig figs)

For question #3, it's asking me for heat, so I did (50.0) x (0.46) x (100.0 - 20.0) and got 1840. (Rounded to sig figs)

For question #4, it's asking me for specific heat, so I did (105 J) / (100.0g) x (25.0 - 10.0) and got 0.070. (Rounded to sig figs)

I still don't understand what I did wrong. I did all of this by hand with all the correct variables at first and I then I tried putting the same values into calculators to find the variables that were being asked for and the calculators are giving me the same answers as what I had above, so what am I doing wrong?
Last edited by username5575986; 8 months ago
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charco
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#4
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#4
(Original post by AntiAW)
Yeah, but the other questions have different equations.

For question #2, it's asking me for temperature change. So, I did (31,500 J) / (750g) x (4.184J/gC) and got 10.0. (Rounded to sig figs)

For question #3, it's asking me for heat, so I did (50.0) x (0.46) x (100.0 - 20.0) and got 1840. (Rounded to sig figs)

For question #4, it's asking me for specific heat, so I did (105 J) / (100.0g) x (25.0 - 10.0) and got 0.070. (Rounded to sig figs)

I still don't understand what I did wrong. I did all of this by hand with all the correct variables at first and I then I tried putting the same values into calculators to find the variables that were being asked for and the calculators are giving me the same answers as what I had above, so what am I doing wrong?
So what's the problem? You seem to have all the correct answers!
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username5575986
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#5
Report Thread starter 8 months ago
#5
(Original post by charco)
So what's the problem? You seem to have all the correct answers!
I apologize for not explaining this earlier, but the assignment that I am doing is online and it is being graded by a computer program. On this type of assignment, my teacher previously put in all of the answers that are supposed to be "correct," so it might be a mistake on his part or maybe the program is just acting weird. I'm not sure, but I have emailed him, so hopefully he knows what is wrong.
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Maya.kg16
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#6
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#6
It’s possibly because you haven’t stated units?
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username5575986
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#7
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#7
(Original post by Maya.kg16)
It’s possibly because you haven’t stated units?
The instructions on the assignment say "Solve for the unknown variable using the specific heat formula. Input your answer (without units) and using the correct number of sig figs."
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username5575986
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#8
Report Thread starter 8 months ago
#8
(Original post by Maya.kg16)
It’s possibly because you haven’t stated units?
Nevermind, I think I was rounding to the wrong sig figs.
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