Thermal physics; specific heat capacity

[saccapella]

Homework Statement

In an experiment to measure the temperature of the flame of a Bunsen burner, a lump of copper of mass 0.12 kg is heated in the flame for several minutes. The copper is then transferred quickly to a beaker, of negligible heat capacity, containing 0.45 kg of water, and the temperature rise of the water measured.

a)Temperature of water rises from 15 to 35degrees. Calculate thermal energy gained by the water.
b)Calculate the temperature reached by the copper in the flame. Assume no heat is lost when copper is transferred.

Specific heat capacity of water = 4200jkg^-1K^-1
Specific heat capacity of copper = 390jkg^-1K^-1

Homework Equations

Q=mc(final temperature - initial temperature)

The Attempt at a Solution

a)Q=0.45*4200*20
Q=3.78*10^4J

b)none... this is where i got stuck :/ help please!

 

[gneill]

The heat that ended up raising the water's temperature came from somewhere. Where did it come from?

 

[saccapella]

The heat that ended up raising the water's temperature came from somewhere. Where did it come from?

The copper?

 

[gneill]

The copper?

Yes, the copper. How much heat did it give up to the water? What is the copper's final temperature?

 

[saccapella]

Yes, the copper. How much heat did it give up to the water? What is the copper's final temperature?

3.78*10^4J...

3.78*10^4J=0.12*390*change in temperature

so change in temperature = 808?

This is where I get stuck on...I don't know how to find the final temperature

 

[gneill]

What is the final temperature of the copper as it sits in the water bath?

 

[saccapella]

What is the final temperature of the copper as it sits in the water bath?

35 degrees

Edit: Misread what you said lol, final temperature of the copper as it sits in the water bath? 843?

 

[gneill]

Right. The copper and water reach temperature equilibrium. So T_f = 35, and you're looking for T_i for the copper. If Q is your heat value, m_c the copper mass and c_c the copper specific heat capacity, then

Q = m_c*c_c*ΔT

where ΔT is the difference between the initial and final temperatures (I've assumed all positive values for simplicity).

 

[gneill]

35 degrees

Edit: Misread what you said lol, final temperature of the copper as it sits in the water bath? 843?

No, no, you were correct the first time (before edit). The water and copper reach an equilibrium temperature of 35 degrees. 843 degrees, then, is the initial temperature of the copper when it is first placed into the water.

 

[saccapella]

Ohh, I see what you did. Thanks!

 

[ally.hady]

gold penny lab, i remmber doing this it was fun. sorry we didint have these questions, maybe you should search for gold penny lab.