Question

What is the total heat evolved when a saturated solution of boric acid (H3BO3) in water is cooled from 100C to 20C? Note the specific heat capacity of the saturated solution is approximately that of water in that temperature range (4.20 J/g.K) and the specific heat capacity of the solid is approximately 0.

As we are not given mass do I use the equation q = m x c x ∆T and assume mass of 100g, or can I assume constant pressure and use the equation q(p) = C(p) x ∆T?

Thanks!

Answer 1

I don't think you can assume either. And q = mcdelta T IS q(p); i.e., q at constant p. Also, I don't think this problem can be solved without knowing the volume or mass of the saturated solution. Obviously a 200 g sample will evolve more heat than a 100 g sample.