AnswerMass of Aluminum: Calculating Heat Transfer to Reach Final Temp

[DrMcDreamy]

Homework Statement

I think this is more of a gen chem question, but this is for my physics lecture.

A student drops two metallic objects into a 240 g steel container holding 62 g of water at 24◦C. One object is a 186 g cube of copper that is initially at 75◦C, and the other is a chunk of aluminum that is initially at 4.6◦C. To the student’s surprise, the water reaches a final temperature of 24◦C, precisely where it started. What was the mass of the aluminum chunk? Assume the specific heat of aluminum and copper is 900 J/kg ·◦C and 387 J/kg ·◦C,respectively. Answer in units of kg

Homework Equations

What is the formula that I am supposed to use for this? TIA

 

[tweety1234]

Homework Statement

I think this is more of a gen chem question, but this is for my physics lecture.

A student drops two metallic objects into a 240 g steel container holding 62 g of water at 24◦C. One object is a 186 g cube of copper that is initially at 75◦C, and the other is a chunk of aluminum that is initially at 4.6◦C. To the student’s surprise, the water reaches a final temperature of 24◦C, precisely where it started. What was the mass of the aluminum chunk? Assume the specific heat of aluminum and copper is 900 J/kg ·◦C and 387 J/kg ·◦C,respectively. Answer in units of kg

Homework Equations

What is the formula that I am supposed to use for this? TIA

Q = mcT

 

[DrMcDreamy]

Copper:
Q=mc\DeltaT
Q=(.186 kg)(387 J/kg C)(24 C -75 C)
Q=-3671.1 J

Aluminum:
But I am not given Q, so I have to solve for 2 things: Q and m
Q=mc\DeltaT
Q=m(900 J/kg C)(24 C -4.6 C)
Qm=(900 J/kg C)(19.4 C)
Qm=17,460 J/kg
Which doesn't make sense.

So what do I do?

 

[Borek]

You are given Q for Al, although not directly - think, what it means that the temperature has not changed?

Besides, watch your algebra:

Q=m(900 J/kg C)(24 C -4.6 C)
Qm=(900 J/kg C)(19.4 C)

Second doesn't follow from the first.