Solving Mass of N Loss from Cu at 20C to 77.3K

[~christina~]

[SOLVED] Mass of N loss

Homework Statement

1.00kg block of Cu at 20C is dropped into a large vessel of liq Nitrogen at 77.3K. How many kg of Nitrogen boil away by the time the copper reaches 77.3K?
specific heat of Cu is 0.0920cal/g C. The latent heat of vaporization of Nitrogen is 48.0cal/g

Homework Equations

$$Q= mc\Delta T$$
$$Q= \pm mL$$
$$Q_{cold}= -Q_{hot}$$

The Attempt at a Solution

I'm not sure how to do this problem but I know what equations are needed.
L= 48.0cal/g
$$M_{cu}= 1.00kg$$
$$M_{N}= ?$$
$$T_f= 77.3K= -195.85^oC$$
$$T_i= 20^oC$$

Do I just solve for mass of the Nitrogen after I equate the 2 energy equations together?
like this:
$$- M_{Cu}C_{Cu}\Delta T= M_{Nitrogen}L$$


Help please.

Thank You

 

[Kurdt]

Yes you would solve for the mass of nitrogen since the energy from the copper will be the energy used to change the nitrogen from liquid to solid.

 

[~christina~]

Yes you would solve for the mass of nitrogen since the energy from the copper will be the energy used to change the nitrogen from liquid to solid.

Thanks a lot Kurdt