Finding Specific Heat of Brass

[iggy_gim]

Hey guys,

So i am currently trying to figure a problem out that our teacher came up with.

 

A brass weight whose mass is 200 g (0.2kg) is heated in a hot water bath on a hot plate.  After heating for three minutes, it is transferred to a calorimeter filled with 175 grams (0.175 kg) of water.  The calorimeter is left to sit and is measured five minutes later to have a net temperature change of 7 K.  What is the specific heat of brass assuming that the calorimetric constant is 195 J K^-1 and the specific heat capacity of water is 4200 J K^-1 kg^-1.

 

It seems to me it is missing the initial temperature of the boiling water/brass to find the temperature change of the brass.  Am I correct in thinking this?

 

Thanks

[Baller97]

Hey guys,

So i am currently trying to figure a problem out that our teacher came up with.

 

A brass weight whose mass is 200 g (0.2kg) is heated in a hot water bath on a hot plate.  After heating for three minutes, it is transferred to a calorimeter filled with 175 grams (0.175 kg) of water.  The calorimeter is left to sit and is measured five minutes later to have a net temperature change of 7 K.  What is the specific heat of brass assuming that the calorimetric constant is 195 J K^-1 and the specific heat capacity of water is 4200 J K^-1 kg^-1.

 

It seems to me it is missing the initial temperature of the boiling water/brass to find the temperature change of the brass.  Am I correct in thinking this?

 

Thanks

(Using the equation of q=mcdeltaT), q=0.2 x 4.2 x 7= 5.88 kJ mol^-1

You don't need the initial temperature. Delta T means the change in temperature between the initial and final, so you should use that for delta T and you'll be good.

[Vioh]

(Using the equation of q=mcdeltaT), q=0.2 x 4.2 x 7= 5.88 kJ mol^-1

You don't need the initial temperature. Delta T means the change in temperature between the initial and final, so you should use that for delta T and you'll be good.

 

I don't really know what you are calculating here, but it's clear that you haven't gotten the result for the specific heat capacity of brass.

 

Due to conservation of energy & due to the law of thermodynamics, the real equation should be:

0.2 × c_brass × ΔT_brass = 0.175 × 4200 × 7 + 195 × 7 (where ΔT_brass≠ 7)

 

Since there're 2 unknowns in the equation (c_brass and ΔT_brass), it's impossible to solve for the specific heat capacity of brass. Unless there's another method of approaching this question, I would agree with iggy_gim that:

 

It seems to me it is missing the initial temperature of the boiling water/brass to find the temperature change of the brass.  Am I correct in thinking this?