Specific heat

[Macg73]

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

[Klaynos]

This looks like homework help.

 

2 points though.

What are the equations for heat capacity that you know?

Is there a phase change here?

[swansont]

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.

[ecoli]

This looks like homework help.

 

moved

[insane_alien]

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

[swansont]

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.

[insane_alien]

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

[swansont]

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.

[insane_alien]

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

[swansont]

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.