Hi, I am stuck on this question and would really appreciate some pointers on how to solve it,

 

The specific heat capacity of the lava is 1600 J kg^-1 oC^1. when all the erupted lava cools from the eruption temperature of 1050 degrees Celsius to 15 degrees celsius, the heat released is 2 x 10 ^15 J.

I need to calculate a value for the total mass of lava that erupted.

 

Many thanks for any advice

This looks like homework help.

 

2 points though.

What are the equations for heat capacity that you know?

Is there a phase change here?

As the units imply, the specific heat capacity tells you how much energy per degree per kg it takes to heat or will be given off by cooling the substance.

 

So [math]Q = mc\Delta T[/math]

 

However, this does not account for heat of fusion as it solidifies, and solids will typically have a different heat capacity as it cools below this point.

 

So either it's a really badly written question, and you need to solve for m, or there's more information needed.

This looks like homework help.

 

moved

it could mean after the lava has solidified, maybe. unless it gives you a heat of fusion just use dH=mCpdT

it could mean after the lava has solidified, maybe. unless it gives you a heat of fusion just use dH=mCpdT

 

But it gives the eruption temperature as the starting point. There's either bad geology or bad physics here, methinks.

anyone know what the heat of fusion for lava is anyway?

anyone know what the heat of fusion for lava is anyway?

 

I would imagine it's going to depend on the chemical composition. There are different types of lava.

that makes sense. i was just wondering if anybody had actually bothered to measure it

that makes sense. i was just wondering if anybody had actually bothered to measure it

 

I would say yes. e.g.

 

http://adsabs.harvard.edu/abs/1985E&PSL..73..407F

http://www.agu.org/pubs/crossref/1995/95GL02064.shtml

 

There are lots of links to different compositions. Though it seems that not only does composition matter, but whether you have a eutectic mixture or not matters, too.